Dreams and dreaming have been topics of philosophical inquirysince antiquity. Historically, the topic of dreaming has mostly beendiscussed in the context of external world skepticism. As famouslysuggested by Descartes, dreams pose a threat towards knowledge becauseit seems impossible to rule out, at any given moment, that one is nowdreaming. Since the 20^th century, philosophical interest indreaming has increasingly shifted towards questions related tophilosophy of mind. What exactly does it mean to say that dreams areconscious experiences during sleep? Do dreams have duration, or arethey the product of instantaneous memory insertion at the moment ofawakening? Should dreams be described as hallucinations or illusionsoccurring in sleep, or should they rather be described as imaginativeexperiences? Do dreams involve real beliefs? And what is therelationship between dreaming and self-consciousness?

This entry provides an overview of the main themes in thephilosophical discussion on sleep and dreaming and emphasizes theconnection between issues from different areas of philosophy. Becauserecent philosophical work on dreaming has taken on a distinctlyinterdisciplinary flavor, this entry also includes pointers to therelevant scientific literature and gives several examples of howevidence from scientific sleep and dream research has informed thephilosophical debate, andvice versa.

• 1. Dreams and epistemology
  • 1.1 Cartesian dream skepticism
  • 1.2 Earlier discussions of dream skepticism
  • 1.3 Dreaming and other skeptical scenarios
  • 1.4 Cartesian dream skepticism and real-world dreams
• 2. The ontology of dreams
  • 2.1 Are dreams experiences?
  • 2.2 Dreams as instantaneous memory insertions
  • 2.3 Empirical evidence on sleep and dreaming
  • 2.4 Dreams and hallucinations
  • 2.5 Dreams and illusions
  • 2.6 Dreams as imaginative experiences
  • 2.7 The problem of dream belief
• 3. Dreaming and theories of consciousness
  • 3.1 Dreaming as a model system and test case for consciousness research
  • 3.2 Dreams, psychosis, and delusions
• 4. Dreaming and the self
• 5. Immorality and moral responsibility in dreams
• 6. The meaning of dreams and the functions of dreaming
  • 6.1 The meaning of dreams
  • 6.2 The functions of dreaming
• 7. Conclusions
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Dreams and epistemology

1.1 Cartesian dream skepticism

The most famous and most widely discussed philosophical problemraised by dreaming is whether dreams pose a threat towards ourknowledge of the external world (see Williams 1978; Stroud 1984;Newman 2010; Klein 2014). Descartes illustrates the problem in aparticularly compelling manner in theMeditations, where heuses the dream example to motivate skepticism about sensory-basedbeliefs about the external world, including his own bodilyexistence. Dreams are clearly not the only case in which sensoryexperience can lead us astray; familiar cases of sensory illusionsshow that perception is not always reliable. Yet, as Descartes notes,these cases are too easily avoided to raise general doubts about thereliability of sensory perception. The same is not true, however, fordreaming. Dreams suggest that even in a best-case scenario of sensoryperception (Stroud 1984), in which standard cases of misperception (asin seeing very small or faraway objects as too big or too small) canbe ruled out and which consequently seem indubitably certain(Descartes 1641: I.6), sensory deception is possible. EvenDescartes’ realistic experience of sitting dressed by the fireand looking at a piece of paper in his hands (Descartes 1641: I.5)could be nothing but a dream.

There are different ways of construing the dream argument. Aparticularly drastic claim would be that Descartes might conceivablybe trapped in a lifelong dream in the sense that none of hisexperiences, including his waking experiences, have ever been causedby external objects (Newman 2010 calls this theAlways DreamingDoubt). A weaker claim is that while he is not always dreaming,he cannot rule out, at any given moment, that he is now dreaming(theNow Dreaming Doubt; for a fuller discussion of bothversions, see Newman 2010). This weaker claim is stillepistemologically damaging: even though some of his sensory-basedbeliefs might be true, the possibility that he might now be dreamingrenders him unable to distinguish his true beliefs from those that arefalse. His doubt thus prevents him from possessing sensory-basedknowledge about the world.

The general form of Cartesian-style skeptical arguments can bereconstructed as follows (this standard reconstruction is quoted fromKlein 2014):

1. If I know thatp, then there are no genuine grounds fordoubting thatp.
2. U is a genuine ground for doubting thatp.
3. Therefore, I do not know thatp.

If we apply this to the case of dreaming, we get:

1. If I know that I am sitting dressed by the fire, then there are nogenuine grounds for doubting that I am really sitting dressed by thefire.
2. If I were now dreaming, this would be a genuine ground fordoubting that I am sitting dressed by the fire: in dreams, I haveoften had the realistic experience of sitting dressed by the fire whenI have actually been lying undressed in bed!
3. Therefore, I do not know that I am now sitting dressed by thefire.

It is also important to see what the dream argument does not do. Inparticular, the dream argument casts doubt only on sensory-basedbeliefs about the external world—of which Descartes’belief that he is sitting dressed by the fire is a particularly clearexample. At the same time, however, Descartes insists that truths of avery general kind, which are not based on sensory perception and donot concern actual existence (such as that 2+3=5 or that a square hasno more than 4 sides), are knowable even if he is now dreaming:

although, in truth, I should be dreaming, the rulestill holds that all which is clearly presented to my intellect isindisputably true. (Descartes 1641: V.15)

Even in dreams, the evidence of reason, or soDescartes would have it, is trustworthy. Consequently, dreams do notundermine our ability to engage in the project of rational inquiry(Frankfurt 1970; but see Broughton 2002), and the possibility ofdream deception is limited to sensory-based beliefs.

1.2 Earlier discussions of dream skepticism

Dream arguments have been a staple of philosophical skepticismsince antiquity and in fact were so well known in the 17^thcentury that in his objections to theMeditations, Hobbes(1641) criticized Descartes for not having come up with a moreoriginal argument and boring the reader with the all-too-familiarscenario of dream deception. Yet, it is has been Descartes’version of the problem that has been most prominent in thephilosophical discussion.

A first reason is that Descartes’ version of the problem setsthe dream argument apart from other related skeptical arguments:unlike standard cases of sensory misperception, dreaming raisesgenuine doubts about the veracity of even best-case scenarios ofsensory perception, and unlike the evil genius hypothesis (see nextsection), dreaming is cast as a real-world (and not a merelyhypothetical) example of sensory deception. By contrast, many whodiscussed the dream example before him did not take theepistemological threat posed by dreaming to be unique. IntheTheaetetus (157e), Plato has Socrates discuss a defect inperception that is common to

dreams and diseases, including insanity, andeverything else that is said to cause illusions of sight and hearingand the other senses,

concluding that knowledge cannot be defined interms of perception (see Chappell 2013). By contrast, Descartesthought that dreams pose a more serious threat to sensory-basedknowledge than (avoidable) cases of sensory illusions. He also thoughtthat dreams leave our ability to engage in rational inquiry intact,thus setting them apart from insanity and delusions. Dreams alsoappear in the canon of standard arguments (or modes) used by thePyrrhonists to counter any knowledge claims, with the fourth of thesearguments stating that the deliverances of the senses vary indifferent conditions such as health, illness, sleep, waking, joy orsorrow and hence are not to be trusted (Diogenes Laertius,Livesof Eminent Philosophers; Sextus Empiricus,Outlines ofPyrrhonism). Augustine (Against theAcademics;Confessions) acknowledges the dream problem,but tries to contain it by arguing that even if we are deceived whiledreaming, we can at least distinguish dreams and illusions from actualperception retrospectively (see Matthew 2005: chapter 8 fordiscussion). And Montaigne (The Apology for Raymond Sebond),alluding to a variety of sensory illusions, notes that wakefulnessitself is infested by reveries, which in some sense are a worseepistemological threat than nocturnal dreams. On this view, dreamdeception is no longer set apart even from standard wake states, butrather is used in a metaphorical sense referring to any type ofsensory deception.

But there is another reason why Descartes’ version of theproblem has been particularly influential. This has to do with theunique style of theMeditations. As Frankfurt (1970) pointsout, the first-person narrator of theMeditations is aneveryman, whose epistemic situation is in no way idiosyncratic (aswould be the case if he were insane), but rather representative of thetypical defects of any human mind. The intimate tone oftheMeditations fits Descartes’ strategy of starting outfrom commonsense arguments and gradually working towards a morerefined philosophical position (Frankfurt 1970: 5), thereby enhancingtheir psychological effect on the reader. The dream argument is acompelling example of this. By first inviting the reader to considerthe apparent indubitability of best-case scenarios of sensorydeception and then using the dream of sitting by the fire to shatterthis certainty, Descartes is appealing to his readers’imagination and previous experience and assuming that they, like him,will have had many such dreams themselves.

Finally, much attention has been devoted to several dreamsDescartes reportedly had as a young man and that according to hisbiographer Adrien Baillet (1691) embodied the theoretical doubts andthe project of pure inquiry he later developed intheDiscourse andMeditations (see also Leibniz1880: IV; Cole 1992; Keefer 1996). Based on his reading of the dreams,Hacking even suggests that for Descartes, dream-skepticism was“alive skepticism […], that is, not a merephilosophical position, but genuine doubt” (Hacking 2001:252). Prominent researchers such as Freud (1940) andRechtschaffen (personal communication, quoted in Cole 1992: 213) haveattested to the authenticity of Descartes’ dreams, but others haveargued that the reports might be fabricated (Clarke 2006: 58–66,Browne 1977).

1.3 Dreaming and other skeptical scenarios

The inherent appeal to empirical plausibility is also what setsCartesian dream skepticism apart from alternative versions ofexternal-world skepticism such as theevil genius hypothesis,thebrain-in-a-vat thought experimentandMatrix-style scenarios of deception. The first of theseis introduced by Descartes in theFirst Meditation. Afterdiscussing the dream argument, Descartes introduces the possibility ofan omnipotent but evil genius determined to deceive us even in ourmost basic beliefs. While he presents the scenario of dream deceptionas something that has often actually happened to him, he emphasizesthat theevil genius hypothesis is a mere fiction intended toaid him in his systematic doubt (Meditations,I.15–16). Still, the evil genius hypothesis radicalizes thedream argument in two respects. One, it is intended to undermine notonly Descartes’ sensory-based beliefs, but also those types ofbeliefs he thought were protected from the dream argument. Two, unlikethe weaker reading of the dream argument introduced above, it involvesa continuing rather than a temporary form of deception.

Thebrain-in-a-vat thought experiment introduces aslightly modernized version of theevil geniushypothesis. The basic idea is that you are nothing but adisembodied brain in a vat containing nutrient fluids andappropriately stimulated by evil scientists or a supercomputer, withthe result that your conscious experience is exactly the same as itwould be if you were an ordinary, embodied human being (see Putnam1981 for a vivid description and refutation of the brain-in-a-vatthought experiment based on content or semantic externalism; seeBrueckner 2012 for discussion). A popular version is introduced intheMatrix-trilogy, which has its protagonists living theirlives in an unrecognized computer simulation while in fact, they arelying in pods. Unlike the classicalbrain-in-a-vat thoughtexperiment, matrixers are essentiallyembodied brains in vats(for a detailed discussion of how the Matrix relates to the otherskeptical scenarios discussed here, see Chalmers 2005).

What distinguishes all three scenarios from the dream argument isthat while the former appeal to logical or even nomologicalpossibility, dream deception is commonly regarded as a regularlyrecurring actuality (cf. Windt 2011; see, however, Bostrom 2003 for anargument intending to show that there are good reasons for thinkingthat we are actually, and not just hypothetically, living in acomputer simulation). Yet, even purely hypothetical skepticalscenarios may enhance their psychological force by capitalizing uponthe analogy with real-world dreams. Clark (2005) argues thattheMatrix systematically equivocates between different usesof the concept of dreaming, where one involves“industrial-strength deception”, or instances in whichboth sensory experience and intellectual functioning are exactly thesame as in standard wake-states, and the other involves real-worlddreams that actually differ from standard wake states, for instance by involvingcompromised critical thinking and bizarre occurrences such as suddenshifts in visual imagery. This systematic ambiguity, according toClark, is what makes theMatrix scenario so compelling.

1.4 Cartesian dream skepticism and real-world dreams

All of this raises the question of whether Descartes’scenario of dream deception is really empirically plausible bycapturing what it is typically like to dream. At the end oftheSixth Meditation, Descartes himself suggests that this isnot the case. Contrary to his remarks in theFirstMeditation, he notes that dreams are in fact quite different fromwaking experiences, for instance in that they are only rarelyconnected to waking memories and in that persons may suddenly appearor disappear in dreams. Indeed, he uses this more sophisticatedphenomenological description (Frankfurt 1970) to introduce the famouscoherence test of dreaming and wakefulness. Contrary to his earlierremarks in theFirst Meditation, he thinks he has now found amark by which dreaming and wakefulness can be distinguished(cf.Meditation I.7):

But when I perceive objects with regard to whichI can distinctly determine both the place whence they come, and thatin which they are, and the time at which they appear to me, and when,without interruption, I can connect the perception I have of themwith the whole of the other parts of my life, I am perfectly surethat what I thus perceive occurs while I am awake and not duringsleep. And I ought not in the least degree to doubt of the truth ofthese presentations, if, after having called together all my senses,my memory, and my understanding for the purpose of examining them, nodeliverance is given by any one of these faculties which is repugnantto that of any other: for since God is no deceiver, it necessarilyfollows that I am not herein deceived. (Meditation VI. 24)

He concludes that dreaming is no longer aserious threat to sensory-based knowledge: even if the coherence testis too demanding to be carried out in every instance of perception,we now at least in principle have the means to rule out that we aredreaming at any given moment.

Several of Descartes’ contemporary critics claimed, however,that the coherence test itself is too error-prone to be of use. Hobbes(1641) argues that if it is possible that someone could merely dreamof successfully performing the coherence test, the test is useless.Similarly, Bourdin (1641) criticizes Descartes’ reliance onclear and distinct ideas as indicators of genuine insight(seesection 1.2) as insufficient, arguingthat one does occasionally dream of having a particularly clear anddistinct insight and only realizes upon awakening that this impressionwas false. He then argues that dreams, contrary to Descartes’own claims, should lead us to doubt even our most basic beliefs aboutmathematical truths. Both Hobbes and Bourdin, then, are challengingDescartes’ characterization of what it is actually like todream—and it should be clear that these diverging statementsabout what we do (or do not) typically dream about are at least inprinciple open to empirical investigation. Indeed, the allegedincoherence of dreams is closely related to empirical work on dreambizarreness, which investigates the occurrence of discontinuities(e.g., sudden, disconnected jumps in the dream narrative),incongruencies (e.g., the appearance of objects or dream charactersout of their proper context, such as George Clooney suddenly sittingin my kitchen) and vague or undefined objects or persons in dreams(see Hobson 1988; Revonsuo & Salmivalli 1995).

Other authors have tried to use research findings to limit or evenescape the threat of dream deception. Grundmann (2002) appeals toscientific dream research to introduce an introspective criterion bywhich we can determine that we are awake rather than dreaming. Becausecritical reasoning abilities are typically absent in dreams, he arguesthat when we introspectively notice that we are able to engage incritical reflection and when ongoing experience is seamlesslyintegrated with our memories, we have good reason to think that we arenow awake. However, Windt (2011) argues that reasoning is notuniformly absent in the dream state and is often systematicallycorrupted when it does occur. While genuinely rational thought atleast sometimes occurs in dreams, it is not recognizable: we areoccasionally misled by apparently rational thought and criticalreasoning in dreams. She concludes that Grundmann’sintrospective criterion often fails and thus cannot lay skepticalworries to rest.

Either way, an important point is that any version of the dreamargument that appeals to real-world dreams, for instance by makingimplicit assumptions about what it is actually or even typically liketo dream, is open to empirical investigation. Dream research canthus be used, at least in principle, to assess the empiricalplausibility of characterizations of dreaming in the context ofdifferent skeptical and anti-skeptical arguments. This raises theinteresting possibility that any version of the dream argument thatappeals to real-world dreams can at best justify a local form ofskepticism, but cannot show, on pains of becoming self-defeating, thatdreams pose a global threat to knowledge ingeneral(including knowledge about dreams; cf. Stroud 1984; Grundmann2002).

2. The ontology of dreams

2.1 Are dreams experiences?

Aside from concerns about empirical plausibility, it is importantto note that Cartesian dream skepticism depends on even more basicbackground assumptions. In particular, it assumes that dreams aredeceptive, first, because they are conscious experiences that aresubjectively indistinguishable from standard waking experiences andsecond, because they involve false beliefs. One strategy for refutingCartesian dream skepticism in the newer literature has been to question these assumptions and deny either that dreams areexperiences at all (Malcolm 1956), or that they are deceptive in theways envisioned by Descartes. A common strategy is to allow thatdreams are experiences but deny either that they involve falsepercepts or that they involve false sensory-based beliefs, or both(Ichikawa 2008; seesection 2.6). For thisreason, the epistemological problem of dream skepticism is bothhistorically and systematically related to newer treatments ofdreaming in philosophy of mind.

This connection can be seen most clearly in Malcolm’sanalysis of dreaming. Malcolm (1956) argues that attempts to conceiveof dreams as experiences during sleep are senseless and that dreamsconsequently provide no foothold for philosophical skepticism. His keyclaim is that “if a person is inany state ofconsciousness it logically follows that he is not sound asleep”(Malcolm 1956: 21). On this view, external-world skepticism motivatedby dreaming can be refuted by defending internal-world skepticismabout the experiential status of dreaming. Inspired by some remarks ofWittgenstein’s (1953: 184; see Chihara 1965 for discussion),Malcolm argues that

the concept of dreaming is derived, not fromdreaming, but from descriptions of dreams, i.e., from the familiarphenomenon that we call “telling a dream”. (Malcolm 1959:55)

It follows that retrospective dream reports arethe sole criterion for determining whether a dream occurred and thatthere is no independent way of verifying the occurrence of dreams insleep. Sentences about dreaming differ from first-person, past-tensepsychological sentences because the latter, unlike the former, are atleast in principle verifiable by independent observations (at leastthis was Malcolm’s view; for a discussion of counterexamples,see Canfield 1961; Siegler 1967; Schröder 1997). According toMalcolm, dream reports and waking memory reports are governed bydifferent grammars and it would be mistaken to infer that an identityof experience lies behind them:

If a man had certain thoughts and feelings in adream it no more follows that he had those thoughts and feelings whileasleep, than it follows from his having climbed a mountain in a dreamthat he climbed a mountain while asleep. (Malcolm 1959/1962:51–52)

On this view, dream thoughts and feelings do notcount as thoughts and feelings at all. For the same reason, it isimpossible to mistakenly think, judge or assert that one is now awakewhile in fact one is dreaming (Malcolm 1956).

An underlying problem with this view is what exactlyMalcolm means by “conscious experience”. While Malcolm(1956) seems to be saying that conscious experience is conceptuallytied to wakefulness, he later claims that speaking of dreams asconscious experiences is unintelligible:

[…] the phrases “mentalactivity”, “mental phenomenon”, “consciousexperience”, are so vague that I should not have known what Iwas asserting. (Malcolm 1959: 52)

He continues to think, however, that ourdefinitions of mental state terms such as “thoughts”,“impressions”, “feelings”,“imagery”, and “beliefs” are sufficientlysharp to be inapplicable to dreaming. If having experiences in sleepinvolves having thoughts, impressions, beliefs etc. in sleep, thendreams are not, according to Malcolm, experiences.

An important consequence of this view is that because dreamreports, for Malcolm, are the sole criterion of dreaming, there can beno additional observational evidence for saying that a person is nowasleep and dreaming. According to Malcolm, contemporaneous evidencesuch as sleepwalking or sleeptalking could not count as evidence forsaying that dreams are experiences occurring during deep sleep,because they would show that the person in question was at leastpartially awake. Similarly, any attempts to adopt a physiologicalcriterion of dreaming (such as EEG measures of brain activity duringsleep) would change the concept of dreaming. Hence, according toMalcolm, empirical evidence is irrelevant for the study of dreamingand attempts to study dreams scientifically are misconceived.

Malcolm’s analysis of dreaming has been criticized for anumber of reasons (see for instance the essays collected in Dunlop1977). The most profound objection is that Malcolm assumes an overlystrict form of verificationism as well as a naïve view oflanguage and conceptual change.Contra Malcolm, many todayassume that justification does not depend on strict criteria with thehelp of which the truth of a statement can be determined with absolutecertainty, but “on appeals to the simplicity, plausibility, andpredictive adequacy of an explanatory system as a whole”(Chihara & Fodor 1965: 197). But if this is correct, then it mightbe possible to justify theoretical statements about the occurrence ofexperiences during sleep even in the absence of strict criteria, forinstance by using behavioral and/or physiological evidence duringsleep to verify dream reports (Ayer 1960). Even when this cannot bedone, it is not clear that the absence of such evidence sets dreamingapart from other first-person, past-tense psychological sentences thatas a matter of fact can no longer be verified (Siegler 1967;Schröder 1997).

Another important criticism is Putnam’s claim thatMalcolm’s analysis of the concept of dreaming relies on amisguided view of analyticity, according to which philosophers haveaccess to deep conceptual truths that are hidden to laypersons:

the lexicographer would undoubtedly perceive thelogical (or semantical) connection between being a pediatrician andbeing a doctor, but he would miss theallegedly“logical” character of the connection between dreams andwaking impressions. […] this “depth grammar” kindof analyticity (or “logical dependence”) does notexist. (Putnam 1962 [1986]: 306)

A related problem is that even if one acceptsMalcolm’s analysis of the concept of dreaming,

it is a mistake to invest the demonstration thatit is impossible to have experiences while asleep with more importthan it has. It is an observation about our use of the word“experience”, and no more. It does not imply that nothinggoes on in our minds while we dream. (Nagel 1959: 114)

Of course Malcolm would think it did: saying that one had somethinggoing through one’s mind in sleep involves describing dreamingas a (conscious) mental state, which to Malcolm once more is quiteinappropriate. Yet, this only follows if we accept Malcolm’simplicit assumption of the existence of depth grammar and of strict,unchangeable rules for the application of mental state terms. If we donot, then there is no longer an obvious contradiction involved insaying that one has thoughts, feelings or beliefs—or perhapseven experiences—while asleep and dreaming. This should alert usto the fact that purely conceptual arguments of the type proposed byMalcolm do not, on their own, prohibit the application of such mentalstate terms to dreaming (Windt 2013). To the extent that they do, thisis a mere conceptual stipulation and not really informative for aninterdisciplinary investigation of dreaming. Rather, whether dreamthoughts, feelings or beliefs are sufficiently similar to waking onesto count as real instances of their kind is an open question.

From now on, and in keeping with the philosophical discussion ondreaming, I will use the term “conscious experience” as anumbrella term for asking about the occurrence of sensations, thoughts,impressions, emotions etc. in dreams (cf. Dennett 1976). What thesehave in common is that is that they are phenomenal states: there issomething it islike to be in these states for the subject ofexperience (cf. Nagel 1974). Asking about dream experience, then, isto askwhether it is like something to dreamwhileone is dreaming, and whetherwhat it is like is similar to(or relevantly different from) corresponding waking experiences. Notethat these are two different questions: It might be like something todream (and dreams might be experiences in this very general sense),though what it is like to dream might still be different from standardwaking experience. If so, dreams might count as experiences even ifthey do not involve actual instances of sensations, emotions etc.

2.2 Dreams as instantaneous memory insertions

A second important objection to the view that dreams are consciousexperiences during sleep is the claim that it relies on insufficientempirical evidence or is even empirically implausible. A particularlyprominent version of this objection is to say that dreams lacktemporal extension: dreams are instantaneous memory insertionsoccurring at the moment of awakening. The most prominent contemporaryversion, at least in philosophy, is Dennett’s(1976)cassette theory of dreaming. In “Are dreamsexperiences?”, he develops an extended thought experimentintroducing a rival to the received view of dreams as consciousexperiences during sleep. The cassette theory says that dreams are theproduct of two processes: a composition process responsible for thecomposition of dream narratives during sleep and a memory-loadingprocess responsible for the ability to recall the dream uponawakening. Importantly, the only difference between the received viewand the cassette theory is that the former additionally posits aconscious presentation process during sleep. On the received view, itis like something to dream; on the cassette theory, it is only likesomething to recall dreams. Both theories, however, are supposed todeal equally well with the available empirical evidence, for instanceon the relationship between dreaming and REM sleep. The importantpoint, for Dennett, is that it is impossible to distinguish betweenthe two rival theories on the basis of dream recall. The thoughtexperiment thus is not intended to show that dreams arenotexperiences, but rather that the question of whether they are cannotbe settled by armchair conceptual analysis or on the basis ofsubjective testimony, but “only by the triumph of a goodempirical theory over rival empirical theories” (Dennett 1979:317). In this respect, the aims of Dennett’s argument arediametrically opposed to Malcolm’s. InConsciousnessExplained, Dennett (1991) uses a similar thought experiment toundermine the distinction between memory insertion and memory revisionfor waking memory reports (see also Emmett 1978 for a criticaldiscussion of this point).

The basic idea behind Dennett’s cassette theory goes back toa famous dream reported by Maury (1861), in which a long and complexdream about the French revolution culminated in his execution on theguillotine. At this point, Maury awoke to find that the headboard ofhis bed had fallen on his neck. Because the dream seemed tosystematically build up to its dramatic climax, which in turn wasoccasioned, it would seem, by an external stimulus, he and otherssuggested that such cases were best explained as instantaneous memoryinsertions experienced at the moment of awakening. This theory, alsoknown as the Goblot-hypothesis, was discussed by many dreamresearchers, such as Binz (1878), Goblot (1896), Freud (1899), andmore recently Hall (1981; for a discussion from the perspective ofcontemporary dream research, see Kramer 2007:22–24). Dennett’s cassette theory also has philosophicalprecedent, with Gregory (1916) suggesting that dreams are psychicalexplosions occurring at the moment of awakening. It also continues tobe discussed in the contemporary literature. Rosen (2013) argues thatdreams are experiences, but at the same time proposes that Malcolm andDennett were right to raise skeptical worries about thetrustworthiness of dream reports. Hernarrative fabricationthesis says that dream reports are in fact often the product ofconfabulation and fail to accurately describe experiences occurringduring sleep. By contrast, Windt (2013) defends an anti-skeptical viewaccording to which dream reports can, at least under certainconditions, be regarded as trustworthy with respect to previousexperience during sleep.

2.3 Empirical evidence on sleep and dreaming

Whereas Dennett (1976) takes the empirical evidence to be insufficient fordeciding the question of whether dreams are experiences, more recentauthors (Flanagan 2000; Metzinger 2003; Revonsuo 2006; Rosen 2013;Windt 2013) suggest otherwise.

A first reason for thinking that dreams are experiences duringsleep is the relationship between dreaming and REM (rapid eyemovement) sleep. Researchers in the 1950s discovered that sleep is nota uniform state of rest and passivity, but that there is acharacteristic and interindividually stable sleep architectureinvolving different stages of sleep (Aserinsky & Kleitman 1953,1955; Dement & Kleitman 1957). Periods of slow wave sleep (alsocalled non-REM or NREM sleep), so called because of the presence ofcharacteristic slow-wave, high-voltage EEG activity, are followed byperiods of high-frequency, low-voltage activity during REM sleep. Thislatter activity is in fact indistinguishable, using EEG measuresalone, from measures obtained during wakefulness. REM sleep is alsocharacterized by rapid eye movements and a near-complete loss ofmuscle tone. Further characteristics of REM sleep include increasedblood pressure, respiratory rate and pupil diameter as well asirregular heart rate (for details, see Dement 1999: 27–50;Jouvet 1999). Because of this combination of wake-like brain activityand peripheral paralysis, REM sleep is sometimes also calledparadoxical sleep (Jouvet 1999).

Importantly, reports of dreaming are much more frequent followingREM sleep awakenings (81.9%) than following NREM sleep awakenings(43%; Nielsen 2000). The former tend to be more elaborate, vivid, andemotionally intense, whereas the latter tend to be more thought-like,confused, non-progressive and repetitive (Hobson et al. 2000), leadingto the assumption that dreaming is “physicallydiagnosable” (Hobson 1988: 154). Yet, attempts to identifydreaming with mental activity during REM sleep are controversial, andmany now hold that dreams can occur in all stages of sleep (e.g.,Antrobus 1990; Foulkes 1993b; Solms 1997, 2000; Domhoff2003). Nielsen’s (2000)covert REM sleep hypothesis,according to which NREM sleep dreams are associated with sub-thresholdREM activity, is a compromise between both extremes. The controversyabout the sleep-stage correlates of dreaming is further complicated bythe fact that there is currently no standardized and widely accepteddefinition of dreaming (Pagel et al. 2001). It thus seems plausiblethat

differences in definitions of “cognitiveactivity” and/or “dreaming” […] account formuch of the variability in levels of mentation recall from REM andNREM sleep that has been observed in previous studies. (Nielsen 2000:853)

A more differentiated picture of brain activity during sleep andits relation to dreaming is suggested by neuroimaging studies, whichshow that REM sleep is characterized by a shift in regional activationpatterns compared to both wakefulness and NREM sleep (Dang-Vu et al.2007; Nir & Tononi 2010; Desseilles et al. 2011). High activationlevels in the pons, thalamus, temporo-occipital, motor, limbic, andparalimbic areas (including the amygdala), equaling or even surpassingthose seen in wakefulness, fit in well with the predominance of visualand motor imagery during dreams and with the frequency of intense,often negative emotions. The comparative deactivation of thedorsolateral prefrontal and inferior parietal cortices fits in wellwith the cognitive deficits often thought to characterize dreamingsuch as the loss of self-awareness, the absence of critical thinking,mnemonic deficits and the delusional belief in the reality of dreamevents (Hobson et al. 2000). This convergence of neuroscientificevidence and the phenomenology of dreaming thus suggests the outlinesof a naturalistic theory of dreaming. And if we follow Dennett (1976)in thinking that this kind of evidence is relevant for determiningwhether dream sensations and emotions are real instances of theirkind, then this is a compelling reason for saying that dreams are,after all, experiences, in the sense of involving the phenomenology ofseeing, feeling, etc during sleep.

A second line of evidence comes from lucid dreams, or dreams inwhich one knows that one is dreaming and is often able to exercisesome level of dream control (LaBerge 2007). The term lucid dreamingwas coined by van Eeden (1913), but the phenomenon has been known forcenturies. Aristotle (On Dreams) already notes that one cansometimes be aware, while dreaming, that one is dreaming. Yet, manytheorists, including many philosophers (e.g., Sartre 1940) thoughtthat realizing that one is dreaming is incompatible with the dreamstate and that dream lucidity is strictly impossible. Researchersinvestigating lucid dreams in the laboratory, however, have provedotherwise (Hearne 1978; LaBerge et al. 1981). They showed that luciddreamers can use specific, pre-arranged patterns of eye movements(e.g., right-left-right-left) to signal in real-time that they havenow become lucid and are engaging in particular dreamexperiments. Because dream-eye movements correspond to real-eyemovements (as predicted by the so-calledscanning hypothesis;see Dement & Kleitman 1957; Leclair-Visonneau et al. 2010), thesesignals are clearly identifiable on the EOG. Retrospective reportsconfirm that the dreamer really was lucid and signaled lucidity(Dresler et al. 2012; Stumbrys et al. 2014). This technique has beenused to study muscular activity accompanying body movements in dreams(Erlacher et al. 2003; Dresler et al. 2011), for advanced EEG analysisof brain activity during lucid dreaming (Voss et al. 2009), as well asfor first imaging studies (Dresler et al. 2011, 2012). Eye signals canalso be used to measure the duration of different activities performedin lucid dreams—e.g., walking, counting, or performing a simplegymnastics routine (Erlacher et al. 2014). Preliminary evidencesuggests that walking and gymnastics take more time in lucid dreamsthan in wakefulness, but that the duration of counting is roughly thesame. This is exactly the opposite of what would be predicted by thecassette theory, according to which the duration of dream actionsshould be much shorter than in wakefulness.

A third line of evidence comes from dream-enactment behavior(Nielsen et al. 2009), most prominently in patients with REM-sleepbehavior disorder (RBD; Schenck & Mahowald 1996; Schenck 2005;Leclair-Visonneau et al. 2010). Due to a loss of the muscular atoniathat accompanies REM sleep in healthy subjects, these patients showcomplex, seemingly goal-directed behaviors such as running or fightingoff an attacker during REM sleep. Retrospective dream reports oftenmatch the observed behaviors, suggesting that patients are literallyacting out their dreams during sleep. Many contemporary philosophersthink that the evidence from lucid dreaming and dream-enactmentbehavior shows Dennett’s cassette theory to be empiricallyinvalid (e.g., Revonsuo 2006: 77).

The discovery of REM sleep also profoundly altered the theoreticalconception of sleep. Going back to Aristotle (On Sleeping andWaking), sleep had been defined in negative terms as the absenceof wakefulness and perception. This tendency is still found inMalcolm’s claim that “to a person who is sound asleep,‘dead to the world’, things cannot even seem”(Malcolm 1956: 26). With the discovery of REM sleep, sleep came to beregarded as a heterogeneous phenomenon characterized by the cyclicalteration of different sleep stages. REM sleep was now considered as“neither sleeping nor waking. It was obviously athirdstate of the brain, as different from sleep as sleep is fromwakefulness” (Jouvet 1999: 5). The folk-psychological dichotomybetween sleep and wakefulness now seemed oversimplified andempirically implausible.

The changing view of sleep was accompanied by a changedunderstanding of dreaming. Where Aristotle (On Dreams) hadstill allocated dreaming to the residual movements of the sensoryorgans arising during the quiet of sleep and in the absence ofexternal sensory stimulation, researchers from the 19^thcentury onwards believed dreams to occur in an intermediate periodbetween sleep and wakefulness. Even after the discovery of REM sleep,the “paradigm […] of dreaming as half-waking,half-sleeping, persisted” (Jouvet 1999: 5), and researchers onlygradually came to regard REM sleep as a genuine and unique sleepstage. Also, from the 1950s onwards, the scientific study of dreamsfor the first time seemed feasible, and at least initially, the newfields of scientific sleep and dream research developed together. Itwas in this climate that Malcolm (1956, 1959) appealed to the earlierpractice of regarding dream reports as the sole source of evidence forthe study of dreaming and objected to the classification of dreams asexperiences occurring in sleep. According to Malcolm, experiencescould at best occur during half sleep, whereas he followed Aristotlein assuming that dreaming proper occurred during deep sleep. Seen inthis light, Malcolm was as much objecting to the reconceptualizationof dreams as to that of sleep (for an excellent history of the studyof sleep and dreaming, see Kroker 2007).

2.4 Dreams and hallucinations

Granting that dreams are experiences (in the sense of phenomenalexperience, as described above), how can the conscious experience ofdreaming be described conceptually? Throughout the history ofphilosophy, the standard view has been that dreams have the samephenomenal character as waking perception and count as hallucinationsin the philosophical sense, that is, as experiences that aresubjectively indistinguishable from genuine perception but where thereis no mind-independent object being perceived (Crane 2011; Macpherson2013). As is the case for waking hallucinations, dreams seemingly putus in contact with mind-independent objects. Yet, because dreamsunfold in the absence of an appropriate contemporaneous stimulussources, they fit the philosophical concept of hallucination. Notethat this might even be true of false awakenings, or realistic dreamsof waking up in one’s actual sleeping environment. Even if Iseem to see my bedroom in such a dream, and even if I my visualexperience is exactly the same as it would be if I were to open myeyes, this would still not count as a case of sensory perception: aslong as my eyes were closed during the episode, I would not,literally, beseeing my bedroom, but hallucinating it. Infact, this is why false awakening are sometimes thought to be aparticularly compelling reason for endorsing dream skepticism(cf. Russell 1948: 153).

The view that dreams involve hallucinatory experiences is the coreintuition behind Cartesian dream skepticism and implicit inDescartes’ assertion than even if all of my sensory experiencesare false because I am now dreaming,

it is certain that I seem to see light, hear anoise, and feel heat; this cannot be false, and this is what in me isproperly called perceiving (sentire). (Descartes 1641: II.9)

It also lies at the heart of Aristotle’stheory of dreaming (On Dreams), according to which dreamsresult from the movements of the sensory organs that continue evenafter the original stimulus has disappeared. In the silence of sleepand in the absence of any contemporaneous sensory stimulation, theseresidual movements result in sometimes vivid sensory imagery that issubjectively indistinguishable from actual sensoryperception. Similar views of dreams as the after-effects of a priorstimulus were held by many other ancient authors (Dreisbach 2000;Barbera 2008).

While Descartes was troubled by the hallucinatory character ofdreams, Leibniz was fascinated by it, noting that the spontaneousformation of visions in dream is “more elegant than any which wecan attain by much thought while awake”(Leibniz,Philosophical Papers and Letters, Vol. I,177–178). Berkeley (1710: I.18) used the example of dreaming tomotivate his idealist claim that the existence of external bodies isnot necessary for the production of vivid experiences. The onlydifference between dreams and waking experiences, according toBerkeley, lies in the comparative instability and lack of coherence ofdreams (see Downing 2013 for details). A similar intuition underliesRussell’s remarks on dreams in the context of sense-data theory(Huemer 2011). In dreams, according to Russell,

I have all the experiences that I seem to have;it is only things outside my mind that are not as I believe them to bewhile I am dreaming. (Russell 1948: 149–150)

Elsewhere, he goes so far as to claim thatdreams and waking life

must be treated with equal respect; it is only bysome reality notmerely sensible that dreams can becondemned. (Russell 1914: 69)

Here, we see that historically, epistemologicalquestions about dreaming were closely connected to psychologicalquestions and questions from philosophy of mind about the nature andontology of dream experience.

In the context of Hume’s taxonomy of the mind, dreams occupyan interesting intermediate position between impressions, includingsensations, passions and emotions, which enter into the mind“with most force and violence” (Hume 1739: 1.1.1.1), andideas, or “the faint images of these in thinking andreasoning” (Hume 1739: 1.1.1.1). On the one hand, Hume iscommitted to the empiricist claim that as mere creatures of the mind,dreams depend on prior impressions but themselves count as ideas. Onthe other hand, dreams are an obvious counterexample to hisdichotomous distinction between impressions and ideas, because“in sleep, in a fever, in madness, or in any very violentemotions of the soul, our ideas may approach to our impressions”(Hume 1739: 1.1.1.1) and indeed may be subjectively indistinguishablefrom them. Hume’s attempt to distinguish impressions and ideasby their different degrees of vivacity has frequently been criticizedas unclear and unconvincing (for instance famously by Ryle 1949), andhis classification of dreams as ideas seems to exacerbate this problem(Waxman 1994; Broughton 2006).

In the phenomenological tradition, dreams are often discussed inthe context of theories of the imagination, if only to remark thatphenomenologically, they are clearly distinct from waking imaginingsand daydreams and should rather, as is the case for hallucinations andillusions, be classified as perceptions (e.g., Husserl 1904/1905;Conrad 1968; note that this only makes sense if one does not readperception as a success-word or assume that perception is necessarilyveridical). Dreams are experienced as reality; in dreams as inwakefulness, but unlike in waking fantasy and daydreams, we feel,simply, present in a world (Uslar 1964; Globus 1987: 89).

The hallucination view of dreaming finds its strongest expressionin Revonsuo’s claim that

there is nothing in the experience itself, in theactual qualitative character of the experience, that necessarilydistinguishes the dream experience from a corresponding perceptualexperience in the waking state (Revonsuo 2006: 82)

and that

the qualities of dream experience are identicalwith the qualities of waking experience. (Revonsuo 2006: 84)

This claim is central to thevirtual realitymetaphor of dreaming, according to which consciousness itself isessentially dreamlike in that even in wakefulness, perceptualexperience is a kind of online hallucination (see also Metzinger 2003,2009). Again, the idea is that dreams are hallucinatory becausedreaming feels exactly like perceiving, but unfolds independently ofan appropriate external stimulus source, and because both feeldifferent from imagining or daydreaming.

The description of dreams as hallucinations, virtual realities orworld-analogues, popular both in the phenomenological tradition and incontemporary, empirically informed philosophical treatments ofdreaming, is complemented by the scientific literature. According toLlinás & Ribary (1994; Llinás & Paré1991), waking perception is a dream-like state modulated by thesenses. Hobson (1988, Hobson et al. 2000) suggests that the vivid,hallucinatory character of dreaming results from the fact that in REMsleep, the visual and motor areas are activated in the same way as inwaking perception, the sole difference being that dreams rely oninternal signal generation rather than on an external stimuli.Recently, Horikawa and colleagues (2013) were able to use neuroimagingdata gathered during sleep onset to predict with 60% accuracy thetypes of objects described in the corresponding mentationreports. They interpret their results as supporting a“principle of perceptual equivalence”, accordingto which perception and dreaming share a common neuralsubstrate. However, attempts to analogize dreaming and wakingexperience may be premature. Nielsen notes that while existingfindings largely support the “reality simulationperspective” of dreaming, it is currently unknown to what extentsubtle perceptual activities (such as visual search) occur indreams. He argues that improved methods of reporting dreams andspecially trained subjects might be needed to make progress on thisquestion (Nielsen 2010: 595).

There is also some controversy in the psychological literature asto whether dreams should be regarded as hallucinations. Aleman &Larøi (2008: 17) argue that because the concept ofhallucination is often used in clinical contexts, classifying dreamsas hallucinations might ultimately be more misleading than helpful. Bycontrast, ffytche (2007; ffytche et al. 2010) argues that anintegrative neurophenomenological model spanning a wide range ofvisual disorders involving hallucinations should take dreams intoaccount and that both waking hallucinations and dreams should bedistinguished from waking imagery because of their phenomenalcharacter.

2.5 Dreams and illusions

Saying that dreams are hallucinations is not, however, the only wayof making sense of the claim that dreaming has the same phenomenalcharacter as waking perception. An alternative is to say that at leastcertain kinds of dream imagery are illusory in the philosophical senseof an experience in which an external object is perceived as havingdifferent properties from the one it actually has (cf. Smith 2002;Crane 2011. If we applythis to dreaming, it means that dreams do not arise completelyindependently of a contemporaneous external stimulus source, butrather involve distorted perceptions of external stimuli and bodilysensations occurring during sleep. The debate on whether dreaming ishallucinatory or illusory thus hinges on the putative sources ofdreaming.

An early precursor to the view that at least some aspects ofdreaming are illusory is the ancient practice of using dreams todiagnose illness, as practiced for instance in the shrines atEpidaurus. The underlying idea was that during sleep, we are moresensitive to bodily ailments than in wakefulness, thus enabling thefirst and clearest signs of illness to manifest in dreams. This is notquite the same, of course, as saying that certain kinds of dreamimagery involve a misperception of bodily changes or that dreaming assuch is caused by bodily sensations. Still, because this viewassociates the content of dreaming with a heightened sensitivity tothe sleeping body, it is diametrically opposed to the claim, widelyaccepted in the contemporary literature, that during REM sleep, theprocessing of external and peripheral bodily stimuli is almostcompletely blocked (e.g., Hobson et al. 2000; on diagnostic dreams,see GalenOn Diagnosis in Dreams; van de Castle 1994).

Claims about the external or bodily sources of dreaming resurfacedin modern philosophy. Aristotle (On Dreams) had alreadythought that at least some dreams are caused by indigestion. Hobbes,who generally adopts the Aristotelian view that dreams arise fromcontinued movements of the sensory organs during sleep, claims that“dreames are caused by the distemper of some inward parts of theBody” and that this might even help explain different types ofdreams. For instance, “lying cold breedeth Dreams of Feare, andraiseth the thought and Image of some fearfull object” (Hobbes1651: 91). While this is not quite the same as saying that dreams areillusory, appealing to the external causes of dream sensations is atleast a necessary condition for saying that dreams involve distortedperceptions. By contrast, proponents of the hallucination viewtypically emphasize that dreams unfold completely independently ofexternal sensory stimuli (cf. Metzinger 2003; Revonsuo 2006)

Appeals to the bodily sources of dreaming became especially popularin the 19^th and early 20^th centuries. Here,claims about the external (as opposed to wholly internal, orbrain-based) sources of dreaming are also more clearly connected tothe claim that sensory and in particular bodily experiences in dreamsare distorted perceptions of external objects. The idea would then bethat those types of dream imagery that count as misperceptions ofexternal objects are illusory. All (or at least subgroup) of bodilyexperiences in dreams might then be redescribed as involving adistorted perception of the sleeping body. In hisPhilosophy ofSleep, Macnish (1838) argues that dreams are caused by anexcitement of the inner organs, for instance through fever orindigestion, and suggests that dreams can be controlled by changingone’s sleeping position. Bergson (1914) echoes this view,claiming that dreams of flying or floating occur when we become aware,while dreaming, that our feet are not touching the ground. Similarattempts to associate changes in sleeping position with specific dreamcontents, such as flying, were undertaken by Scherner (1861), Vold(1910/1912), and Ellis (1911).

There is, of course, an important distinction to be drawn betweenthe claim that external stimuli canoccasionally beincorporated in dreams and the claim that dreamsgenerallyarise in response to or are caused by external or bodilystimuli. While most would allow the former, the latter is morecontentious, because it suggests that the very process of dreaming iscaused by external stimuli. The latter claim, which is a claim aboutthe typical sources of dreaming, was defended by Wundt, who arguedthat the

ideas which arise in dreams come, at least to agreat extent, from sensations, especially from those of the generalsense, and are therefore mostly illusions of fancy, probably onlyseldom pure memory ideas which hence become hallucinations. (Wundt1896: 179)

There is also an important difference betweenthe claim that external or bodily stimuli are the causally enablingconditions for certain types of dreams to arise and the claim thatdream contents can be satisfactorilyexplained byappealingonly to their external or bodily sources. This wasalready pointed out by Silberer (1919), who acknowledges that manydreams have somatic sources, but denies that this is enough toexplain the unique kind of processing underlying dream formation. Itis at least as important, according to Silberer, to understand thepsychic sources of dreaming.

Methodologically, there is also an important difference between thelargely anecdotal observations made by many proponents of the“Leibreiztheorie” (or somatic-stimulus theory) ofdreaming and systematic and controlled experiments. Weygandt (1893),for instance, used experimental manipulations during sleep tosystematically investigate the influence of breathing, bloodcirculation, temperature changes, urge to urinate, uncomfortablesleeping position and visual or auditory stimulation during sleep ondream content (see Schredl 2010 for details). Methodologicalconsiderations also influenced the philosophical debate on dreaming.Singer (1924) argues that sensory stimulation during sleep and itseffect on dreams can be used as a test case for psychophysical claimsabout the association between sensations and stimulus intensity. Suchclaims, he argues, are potentially threatened by the description ofdreams as involving sensations. He suggests a protocol for solvingthis question experimentally. If dreams are sensations, he argues,then a stimulus such as a hornblast should increase the frequency ofdreams in nearby sleepers as well as the frequency of sound in theirdreams, and it should decrease the range of quality and intensity ofthese dreams. If this were found to be the case, psychophysicalclaims about the correlation of sensations with stimulus intensitywould be compatible with saying that dreams involve sensations.

Indeed, a number of newer studies have found evidence for theintegration of external stimuli such as light flashes, sounds, spraysof water applied to the skin (Dement & Wolpert 1958), thermal(Baldridge 1966), electrical (Koulack 1969), and verbal stimuli(Berger 1963; Breger et al. 1971; Hoelscher et al., 1981), and ofblood pressure cuff stimulation (Nielsen et al. 1995; Sauvageau etal. 1998) in dreams. Two recent studies suggest that interindividualdifferences in dream recall frequency might be related to differentlevels of sensitivity to auditory stimuli, with meaningful stimuliinducing more complex cognitive processing and heightened reactivityin participants with high as compared to participants with low dreamrecall frequency (Eichenlaub et al. 2013; Ruby et al. 2013). Thissuggests that Singer’s (1924) prediction was at least not whollyoff the mark.

While proponents of both the hallucination and the illusion viewcan claim that dreaming is subjectively indistinguishable fromstandard waking experience, proponents of the illusion view sometimesalso appeal to the external and bodily sources of dreaming to explainthe phenomenological differences between dream and waking experience.Several philosophers tried to explain the absence of movement indreams by appealing to the inertia of the sleeping body during sleep.According to Bradley (1894), dreams of being unable to move are notrelated to the absence of motor intentions in dreams. Rather, theabsence of appropriate bodily feedback prevents us from executing ourmotor intentions in our dreams. Similarly, Gregory (1918) argues thatdreams involving frustrated effort or thwarted intentions arise whenthe dream fails to provide the requisite imagery. Because backgroundsensations of touch and movement are lacking in dreams, “thesituation willseem right to the dreamer but itwillfeel wrong” (Gregory 1918: 127). Dreams offrustrated effort follow suit.

Appeals to the external and bodily sources of dreaming have falleninto disfavor in the contemporary literature, both in philosophy andin scientific dream research. REM sleep is commonly described as astate in which external stimulus processing and the outward enactmentof internally experienced dream behavior is almost completely blocked:dreams, on this view, rely exclusively on internal signal generationand unfold in a state of near-complete physical paralysis (Hobson etal. 2000).

It is interesting to note, in this context, that these claims aboutthe functional dissociation between dreams and environmental andbodily stimuli are shared both by proponents of internalistconceptions of conscious experience and by proponents of externalistor sensorimotor theories of perception. For instance, Revonsuo writesthat

the contents of both perceptual and bodilyawareness are, during REM dreaming,totally dissociated fromthe corresponding states of the physical body. (Revonsuo 2006: 92;emphasis added)

Similarly, Noë (2004: 213) takes “itas settled that when we dream there is no dynamic exchange with theenvironment (although this might turn out not to be true)”,suggesting that “neural states alone are sufficient fordreaming.” Unlike Revonsuo, he denies, however, that this showsneural activity alone to be sufficient for perceptual experience. Hepoints out that there are phenomenological differences betweendreaming and wakefulness, noting that dream imagery lacks, forinstance, the stability of waking perception. He then argues thatthis difference can be explained by appealing to the lack of dynamicinteraction with the environment in dreams. So while the two disagreeabout the phenomenology of dreaming, a corresponding debate on theinternal as opposed to external or bodily sources of dreaming nolonger exists in the contemporary philosophical literature.

2.6 Dreams as imaginative experiences

The most important rival to the hallucination view of dreaming inthe contemporary philosophical literature is the claim that dreams areimaginative experiences (Gendler 2013). This is typically construed asan alternative to the claim that dreams involve percepts (i.e.,hallucinations or illusions; McGinn 2004), the claim that they involvereal beliefs (Sosa 2007), or both (Ichikawa 2008, 2009). The claimthat dreams involve imagery rather than percepts comes in differentstrengths and in different variants, and it means different things inthe context of different theoretical accounts. A first way ofunderstanding the imagination view of dreaming is to regard it as aclaim about the phenomenology of dreaming. If we assume, as is commonin the phenomenological tradition, that imagining is distinguishedfrom standard waking perception in that imagining does not involve theexperience of being in a world, and if we additionally assume thatdreaming is a form of imaginative experience, then the sense in whichwe feel present in our dreams might be analogous to cognitiveabsorption or fictional immersion of the type experienced in wakingfantasy, but also in reading a novel or watching a movie (McGinn2004). An example is Sartre’s (1940; see Hering 1947; Globus1987 for critical discussion) claim that dreams are experienced asfictions. Yet, he argues that because the reflective quality of wakingconsciousness is absent in dreams, dreaming is a case in which thefictional world has closed upon itself: the imaginary world ofdreaming captures us so completely that the very concept of reality islost in dreams. Any appearance of reflexive consciousness disrupts andterminates the ongoing dream. This is why Sartre also takes prolongedlucid dreams to be impossible.

More recently, the claim that dreaming is phenomenologically likeimagining and daydreaming rather than perceiving has been taken up byMcGinn (2004, 2005a,b) and Ichikawa (2009). Both also argue thatimagery and percepts are sharply distinguished, claiming thatimagining and perceiving are different kinds of mental states thatcannot be meaningfully placed on a continuum. Indeed, because dreamingis often thought to blur the distinction between imagining andperceiving, showing that dreaming is phenomenologically unlikeperceiving and resembles waking imagination is an important goal forany attempt to argue that imagining and perceiving themselves arecategorically distinct. McGinn (2004) proposes a number of criteriafor distinguishing dreams and waking mental imagery (or what he callsimages) on the one hand from percepts on the other hand. He claims,for instance, that images can bewilled while perceptscannot; thatnothing new can be learned from images, but onlyfrom percepts; that theboundaryandforeground-background structure of the visual fieldresults from anatomical constraints, but that nothing comparable isthe case for images; that percepts are moredeterminate thanimages and that the visual field issaturated and detailed,whereas images are gappy; that images (but not percepts)areattention-dependent; that percepts are characterizedbypresence, whereas imaginary objects areposited asabsent; that the identity of imagined objects isnotrecognized or inferred, but given; that you cansee and thinkof two different things at the same time, whereas thesame is not true of images; and that percepts areonlyoccluded by other percepts, but not by images. Dreamsfall on the side of imagery, according to McGinn, not because they arein every respect like waking imagery; yet, he thinks there are enoughdifferences between dreaming and perceiving to reject the view thatdreams are a hybrid between imagining and perceiving, concluding thatdreams are essentially imaginative experiences. Why exactly, then, shoulddreams be described as imaginative experiences? Instead of discussingall of the supposed differences between dreams and percepts, I focuson those that are commonly taken to be the most relevant and the mostcontroversial.

A particularly important issue for the imagination view of dreamingis whether dreams, like waking imaginings, aresubject to thewill (Ichikawa 2009). Historically, it has been commonly takenfor granted that imagination involves “a special effort of themind” (Descartes 1641:VI, 2) and that unlike perception, which is taken to be whollypassive, imagining is an activity that is at least in principle underour control (Wittgenstein 1967: 621, 633). Because dreams, however,do not seem to be under voluntary control, but rather happen to us,they present an important challenge for the imagination view. Here,imagination theorists claim that dreams, though typically not undervoluntary control, are nonetheless subject to the will and the productof unconscious authorship (McGinn 2004; Ichikawa 2009). On this view,rare instances of lucid control dreams show that dreams are generallyamenable to direct and deliberate control in a way that percepts arenot (Ichikawa 2009).

Dreams are also taken to be unlike percepts in that theylacksaturation (McGinn 2004) and thedeterminacy ofwaking perception (James 1890: 47; Stone 1984). In scientific dreamresearch, the vagueness of dream imagery is one of three main subtypesof bizarreness (together with incongruity and discontinuity; seeHobson 1988; Revonsuo & Salmivalli 1995). Perhaps relatedly, dreamcharacters are often identified not by their behavior or looks, butbyjust knowing (Kahn et al. 2000, 2002; Revonsuo &Tarkko 2002). The question of whether we dream in color is alsothought to be relevant to the issue of whether dreaming resemblesimagining or perceiving. In his review of historical studies on colorin dreams, Schwitzgebel found that while contemporary studies tend tosupport the view that we dream in color, studies from the1930–1960s tended to support the claim that we dream inblack-and-white (Schwitzgebel 2011: 5; cf. Schwitzgebel 2002). Hesuggests different interpretations of this shift in opinions aboutcolored dreaming. The rise first of black-and-white and then of colortelevision may have led to a change from colored to black-and-whiteand back to colored dreaming. Alternatively, dreams may have beeneither black-and white or colored all along, with media exposure onlychanging the way people report their dreams. A final possibility isthat dreams are neither black-and-white nor colored. Again, mediaexposure changed only reports of colored dreaming, but on this view,dreams themselves are indeterminate with respect to color, perhaps inthe manner of fictions or daydreams. Schwitzgebel’s main point,here, is that reports of colored dreaming are unreliable: based on theavailable evidence, it is impossible to determine whether or not weactually dream in color (see Windt 2013 for critical discussion). Thisargument is importantly related to his general skepticism about thereliability of introspection (Schwitzgebel 2011; Hurlburt &Schwitzgebel 2007).

Ichikawa (2009) argues that the imagination view of dreamingprovides a better explanation of the available evidence on dream colorthan the percept view. If dreams, like visual imagery, areindeterminate with respect to color, this would explain why dreamreports are influenced by fiction-based experiences and mediaexposure. An empirical prediction, according to Ichikawa, is thatmedia exposure will change not only reports of dreaming, but alsoreports of waking daydreams. A potential problem for this view,however, is that a number of follow-up studies (Schwitzgebel 2003;Schwitzgebel et al. 2006; Murzyn 2008; Schredl et al. 2008; Hoss 2010)have not found evidence for saying that dreams are indeterminate withrespect to color. The available evidence suggests that a majority ofparticipants report dreaming in color, and a small percentage describegrayscale or even mixed (i.e., partially colored, partially grayscale;see Murzyn 2008) dreams or dreams involving moderate color saturation(Rechtschaffen and Buchignani 1992). For this reason, it would seem that the evidence on color indeterminacy is tooinconclusive to translate into an obvious explanatory advantage of theimagination view as compared to the percept view.

Another challenge for the imagination view is how to explaintheemotional character of dreaming. Dreams are sometimesdescribed as hyperemotional, in that a majority of dreams involvestrong (and often negative) emotions (Merritt et al. 1994; Nielsen etal. 1999; Hobson et al. 2000). By contrast, proponents of theimagination view claim that dream emotions are only “mutedversions of themselves” that lack the “sting” ofreal emotions (McGinn 2004: 111) and that “dreams don’tinvolve emotions, except in the way that fictions do” (Ichikawa2009: 119). A particular challenge is how to deal with nightmares,which can be a cause of genuine suffering to those who experience themfrequently (Blagrove et al. 2004; Germain & Zadra 2009; Nielsen& Levin 2009).

Despite these objections, the imagination view also has a number ofadvantages. By assimilating dreams to a commonplace mental state, suchas waking fantasy and daydreaming, rather than a rare occurrence, suchas hallucinations, it provides a more unified account of mental life(Stone 1984). It also has consequences for Cartesian dream skepticism.If dream pain does not feel like real pain, for instance, there is afail-safe way to determine whether one is now dreaming: one need onlypinch oneself (Nelson 1966; Stone 1984; but see Hodges & Carter1969; Kantor 1970). As suggested somewhat sarcastically by Locke,

if our dreamer pleases to try, whether theglowing heat of a glass furnace, be barely a wandering imagination ina drowsy man’s fancy, by putting his hand into it, he mayperhaps be wakened into a certainty greater than he could wish, thatit is something more than bare imagination. (Locke 1689: IV.XI.8)

Austin thought the phenomenological differences between dreaming and wakefulness to be so obvious that

it is just because we all know that dreamsarethroughout unlike waking experiences that we can safelyuse ordinary expressions in the narration of them; (Austin 1962: 42)

by contrast, claims about the subjectiveindistinguishability of dreaming and wakefulness are, according toAustin (1962: 48), absurd. A problem with this latter view is, ofcourse, that many philosophers have embraced this alleged absurdity,suggesting that appeals to intuitive obviousness are not particularlyreliable where the phenomenology of dreaming is concerned.

It is also important to note that the imagination view of dreamingis not committed to the claim that dreaming literallyfeelslike imagining or that imagining is categorically distinct fromperceiving. In theLeviathan, Hobbes describes dreams as“the imaginations of them that sleep” (Hobbes 1651: 90),and imagination as a “decaying sense” (Hobbes1651: 88). This need not, however, be taken as a phenomenologicalclaim. In particular, he uses the concepts of imagination and fancy todescribe perception as well, noting that sensations seem to be causedby external objects, not by pressure on and movement of the sensoryorgans. Consequently, “their appearance to us is Fancy, the samewaking, that dreaming” (Hobbes 1651: 86). O’Shaughnessy(2002) classifies dreaming as an “imagining-ofconsciousness” (O’Shaughnessy 2002: 430) becauseconsciousness is conceptually tied to wakefulness: consciousnessinvolves knowledge of the external world, reactivity to externalstimuli, and perceptual awareness, all of which are lost in dreams.Yet, it is not clear that he thereby takes dreaming to feel differentfrom waking perception, or that he thinks there is a necessarydistinction between conscious experiences (in the phenomenologicalsense) in dreams and wakefulness. By avoiding such claims, this weakerversion of the imagination view also avoids many of the challenges tostronger versions discussed above.

In the scientific literature, the imagination view of dreaming iscomplemented by cognitive theories of dreaming. According to Foulkes(1978), dreaming is a form of thinking with its own grammar andsyntax. Yet, he allows that

the pictures are sufficiently perceptlikegenerally to lead us to believe, until the moment of our awakening,that we actually are seeing real events. (Foulkes 1978: 5)

Domhoff’sneurocognitive model of dreaming (2001,2003) draws from findings on the partial or global cessation ofdreaming in lesion patients (cf. Solms 1997, 2000) to emphasize thedependence of dreaming on visuospatial skills and on a specificnetwork involving the limbic, paralimbic and association areas of theforebrain. It also integrates evidence that dreaming developsgradually and in tandem with visuospatial skills in children (Foulkes1993a, 1999; but see Resnick et al. 1994) and results from dreamcontent analysis supporting the continuity of dreaming with wakingconcerns and memories (the so-calledcontinuity hypothesis;see Domhoff 2001, 2003; Schredl & Hofmann 2003; Schredl 2006). Nirand Tononi (2010) recently used findings on the relation betweendreaming, visuospatial skills and memory to argue that dreaming“might turn out to be the purest form of imagination” (Nir& Tononi 2010: 97). Yet, they explicitly allow that dreams oftenhave a vivid, hallucinatory quality and regard their claim about theimaginative character of dreaming as one about the flow of informationprocessing in dreams, which they expect to be top-down, as in wakingimagery, rather than bottom-up, as in perception. A number ofresearchers have also begun to consider dreaming in the context oftheories of mind wandering (Schooler et al. 2011) and suggest thatthere is an overlap between the brain areas involved in dreaming andthe default-mode network, a network of brain areas associated withstimulus- or task-independent thought (Pace-Schott 2007, 2013; Domhoff2011; Wamsley 2013; Fox et al. 2013). The philosophical implicationsof this comparison between dreaming and waking mind wandering are onlyjust beginning to be explored (Metzinger 2013 a,b).

2.7 The problem of dream belief

Aside from claiming that dreaming involves imagery rather thanpercepts, the second important strategy for defending the imaginationview is to argue that dream-beliefs are not real beliefs, butpropositional imaginings. Sosa (2007: 4) defends a version of theimagination view according to which dreams involve percepts, butbelieving and intending in a dream does not entail in actuality havingany such beliefs or intentions. Ichikawa (2009) defends the strongerposition that dreaming neither involves percepts nor beliefs.

Denying that dream-beliefs have the status of real-beliefs onlymakes sense before the background of a specific theoretical account ofwhat beliefs are and how they are distinguished from other mentalstates, such as delusions or propositional imaginings (seeSchwitzgebel 2014 for an introduction). For instance, Ichikawa (2009)argues that dream beliefs do not have the same functional role as realbeliefs because they lack connection with perceptual experience andfail to motivate actions. For this reason, he thinks thatinterpretationist or dispositionalist accounts of belief speak againstthe view that dreams involve real beliefs. If we observe a personlying asleep in bed, there are no grounds upon which we could ascribeto them a particular belief, allegedly held within a dream. A moresweeping denial of dream belief involves the claim that dream-beliefscontradict commonsense assumptions about what it means to have abelief. For instance, dream beliefs are often inconsistent withlongstanding waking beliefs, and occasionally, treating them as realbeliefs would require the ascription of two contradictory beliefs tothe sleeping subject. I cannot, it seems, both believe that I am beingchased by a lion and that I am lying peacefully in bed at the sametime (Sosa 2007: 5). Moreover, dream-beliefs are apparently acquiredand discarded without any process of belief revision (Ichikawa 2009:112–113). Similar arguments have been used to deny thatdream-thoughts, judgments, affirmations, assertions, or wonderings arereal instances of their kind (cf. Malcolm 1959; Sosa 2007).

This analysis of dream-beliefs has consequences for skepticism. Ifdream beliefs are propositional imaginings, then we cannot falselybelieve, while dreaming, that we are now awake, but can only imaginethat we are. Indeed, on this version of the imagination view, wecannot believe anything at all while dreaming—and so we alsocannot have any false beliefs, including the false belief that we arenow awake (Sosa 2007). If successful, this inability to have beliefswhile dreaming, or so the argument goes, would protect us from dreamdeception.

It is not at all clear, however, that this line of reasoning canallay Descartes’ worry. As Lewis points out, a person might

in fact believe or realize in the course of adream that he was dreaming, and even if we said that, in such case, heonly dreamt that he was dreaming, this still leaves it possible forsomeone who is asleep to entertain at the time the thought that he isasleep. (Lewis 1969: 133)

And for the same reason one could, of course,entertain the erroneous thought that one is now awake. The questionthen becomes whether beliefs are strictly necessary for dreamdeception or whether other mental states such entertaining, thinkingetc. might be sufficient. For instance, as Reed (1979) argues, dreamscan still count as deceptive even if they do not involve stronglyappraisive beliefs, but only minimally appraisive instancesoftaking for granted. It has also been argued that ifdream-beliefs fall short of real beliefs, this makes the specter ofdream deception more, rather than less, worrisome. Ichikawa (2008)argues that on the imagination view of dreaming, we mistakedream-beliefs for real beliefs and thus are deceived as to the statusof our own mental states. Because we cannot reliably distinguishdream-beliefs from real ones, and because knowing thatprequires knowing that one believes thatp, one can have noreflective knowledge if the imagination view of dreaming turns out tobe correct. In order to escape this persistent vulnerability toskepticism, the imagination theorist would have to deny not just thatdream beliefs, but also that wonderings, thoughts, affirmationetc. are real instances of their kind. This however places aconsiderable burden on the imagination theory, and while one mightwant to accept that dream beliefs are too defective to count as realones, the same might not be true for mere instances of thinking orwondering.

Finally, it is interesting to note that a similar debate existsregarding the status of delusions (see Currie 2000; Currie &Ravenscroft 2002; McGinn 2004; Bayne & Pacherie 2005; Bortolotti2009, 2013; Gendler 2013). A theory of dream belief will ultimatelyalso have to clarify how dream beliefs relate not just to realbeliefs, but also to wake-state delusions.

3. Dreaming and theories of consciousness

3.1 Dreaming as a model system and test case for consciousness research

An important reason for thinking that dreaming is relevant fortheories of consciousness is that dreaming involves a profoundalteration in the conditions under which conscious (in the sense ofphenomenal) experience arises. Moreover, as compared to other alteredstates of consciousness (such as waking hallucinations or illusions)and pathological wake states (such as psychosis or neurologicalsyndromes), dreams occur spontaneously and regularly in healthysubjects. For this reason, many regard dreams as a test case forgeneral theories of consciousness, arguing that any theoreticalaccount of consciousness that strives towards empirical plausibilityshould be able to accommodate dreaming as well.

A first proposal for using dreaming as a research model system inconsciousness research was developed by Patricia Churchland (1988).Drawing from scientific dream research, she appeals not only to theexistence of robust phenomenological differences between wakefulness,dreaming and dreamless sleep, but also to the fact that there arebehavioral criteria for the objective identification of the states ofwaking, dreaming and sleep, possibly even enabling the use of animalsmodels. The research program is further strengthened, according toChurchland, by progress on the identification of the neuronalgenerator producing shifts between these states. Churchland (1988:286) also uses evidence on dream bizarreness to argue thatconsciousness lacks a homogeneous underlying organizing principle andis not, as often thought, a single, unified natural kind.

A second proposal for using dreaming as a research model inconsciousness research is defended by Revonsuo. Unlike Churchland, heassumes that the structure of phenomenal experience is deeply similarin dreaming and in wakefulness. Based on his review of the scientificliterature, he argues that

the dreaming brain brings out the phenomenallevel of organization in a clear and distinct form. Dreaming isphenomenality pure and simple, untouched by external physicalstimulation or behavioural activity. (Revonsuo 2006: 75)

According to Revonsuo, dreaming not only involves phenomenalconsciousness, but also, as he puts it (Revonsuo 2006: 75–82)the fullrange of phenomenal contents, including perceptualcontents, color experiences, and pain. On this view, the differencesbetween dreaming and waking experience are of a fairly superficialkind, related only to the absence of a stable external stimulussource. For this reason, he takes the analysis of dreaming to shedlight on the basic, state-independentstructure of consciousexperience. According to Revonsuo, this consists in the immersivecharacter of dreaming: “dreaming depicts consciousness first andforemost as a subjective world-for-me” (Revonsuo 2006:75). The example of dreaming, for Revonsuo, is an important motivationfor introducing the “world-simulation metaphor ofconsciousness”, according to which consciousness itself isessentially simulational and dreamlike, thus supportingRevonsuo’s favored internalist conception of consciousexperience. Because of his endorsement ofbiological realism,which is the claim that consciousness is a biological phenomenon thatis literally located in the brain (Revonsuo 2006: xvii), he alsothinks that the investigation of the neural basis of dreaming mighthelp locate the phenomenal level of organization in thebrain—once more defending a view that is at odds withChurchland’s reductive account.

A possible problem for both views is their reliance on backgroundassumptions about the phenomenology of dreaming and its associationwith REM sleep, which are, as we have seen, both quite controversial(cf.section 2.3). As Windt & Noreika(2011) argue, persistent disagreement on these issues hampers theintegration of dreams into a general theory of consciousness. In theabsence of a well worked out theory of dreaming and its sleep-stageand neural correlates, proposals for using dreaming as a model systemrun the risk of being premature and oversimplified. Note also thatRevonsuo’s account would be threatened by positions according towhich dream imagery is illusory or imaginative. The former view wouldchallenge his claim that dream imagery arises independently ofexternal sensory stimulation, and the latter would challenge his claimthat dreaming has the same phenomenal character as wakingperception. Both claims, however, are crucial for his attempt to showthat dreaming offers particularly clear support for the“world-simulation metaphor of consciousness”.

Recent accounts appealing to generative models and predictiveprocessing (Clark 2013b; Hohwy 2013) might suggest a new, unifiedaccount of perception, dreaming and imagination. This type of accountstrives to accommodate internalist intuitions by confining thevehicles of phenomenal experience to the brain. At the same time, itacknowledges the existence of phenomenological differences instability, detail and coherence between dreaming and wakefulness ofthe kind that are often pointed out by proponents of enactivist orsensorimotor theories of perception (Noe 2004). The key claim ofpredictive processing accounts is that perception is the outcome of aprocess of hypothesis testing such that the brain routinely optimizesits models of the hidden (external) causes of incoming sensory stimuliin order to generate predictions of its next expectedstates. Predictive processing accounts locate the material vehicles ofconscious experience within the brain, while also affording a strongrole to embodiment and sensorimotor skills in perception, because theysuggest that agents can improve their predictions by engaging inactive inference and systematically altering their sensory inputs(Clark 2013a). Clark argues that on such a model,

systems that know how to perceive an object as acat are thus systems that,ipso facto, are able to use atop-down cascade to bring about the kinds of activity pattern thatwould be characteristic of the presence of a cat. […]Perceivers like us, if this is correct, are inevitably potentialdreamers and imaginers too. Moreover, they are beings who, in dreamingand imagining, are deploying many of the very same strategies andresources used in ordinary perception. (Clark 2013a: 764)

On the one hand, this suggests that dreaming,but also imagination and hallucination depend on the same mechanismas veridical perception, namely hypothesis-testing and generativemodels; on the other hand, it may be a new way of making sense of howperception is directly world-revealing in a way often thought to bedenied by internalist accounts and of how, via active inference, ourbrains become “porous to the world” (Clark 2013a:767). Predictive processing accounts explain the occurrence of dreambizarreness by pointing out that because dreams are largelyunconstrained by external stimuli and hence by prediction errors,representational accuracy, for instance of visual dream imagery, islost during sleep (cf. Hobson & Friston 2012). Moreover, Fletcherand Frith (2008: 52) suggest that

the dream state arises from disruptions inhierarchical Bayesian processing, such that sensory firing is notconstrained by top-down prior information and inferences are acceptedwithout question owing to an attenuation of the prediction-errorsignal from lower to higher levels.

This view thus also offers an explanation of whybizarre occurrences in dreams are often met with uncriticalacceptance.

Dreams have also been suggested as a test case for adjudicatingbetween theories that claim that phenomenal consciousness can bedivorced from cognitive access (e.g., Block 2007) and those that claimthat cognitive access and reportability are necessary for thescientific study of consciousness (Cohen & Dennett 2011).Sebastián (2014) argues that because dreams are experiences,and because during (non-lucid) REM-sleep dreams, the dorsolateralprefrontal cortex as the most plausible mechanism underlying cognitiveaccess is selectively deactivated, dreams provide empirical evidencefor the claim that conscious experience occurs independently ofcognitive access. A challenge for this view is to explain why dreamsnonetheless are often reported upon awakening.

3.2 Dreams, psychosis, and delusions

The second major research program for integrating dreaming into abroader theoretical context is the suggestion of using dreaming as amodel of psychotic wake states. The analogy between dreaming andmadness has a long philosophical history (Plato,Phaedrus;Kant 1766; Schopenhauer 1847). It is continued in Hobson’s claimthat “dreaming is not a model of a psychosis. It is a psychosis.It’s just a healthy one” (Hobson 1999: 44) andGottesmann’s (2006) suggestion of using dreaming as aneurobiological model of schizophrenia. There is now a livelydiscussion on the theoretical and methodological implications of dreamresearch for psychiatry (see Scarone et al. 2007; d’Agostino etal. 2013; see Windt & Noreika 2011 as well as the other papers inthis special issue) and a number of studies have investigateddifferences in dream reports from schizophrenic and healthy subjects(Limosani et al. 2011a,b).

Moving beyond the modeling approach, it may also be fruitful tocompare dreams and specific wake-state delusions. Gerrans (2012, 2013,2014) uses a detailed comparison between instances of charactermisidentification in dreams and delusions of hyperfamiliarity (such asthe Frégoli delusion, in which strangers are mistakenlyidentified as family members, but alsodéjà vu)to support the claim that anomalous experience, and not just faultyreality testing, plays a role in delusion formation. Importantly, thisapproach allows him to take not just the similarities, but also thedifferences between dreams and wake-state delusions seriously. Inparticular, he suggests that a deeper understanding can only be gainedby describing the involvement of the default mode network and itsinteraction with prefrontal systems in dreams and in wake-statedelusions on a case-by-case basis. This humble approach to thecomparison of dreams and delusions thus avoids many of the pitfalls ofmore general, and hence less well-defined, attempts to use dreaming asa model system of standard or altered wake states.

4. Dreaming and the self

The classical problem about the self in dreams concerns theidentity between the dream and waking self. Locke (1689) raises theproblem of personal identity in sleep in the context of his discussionof Descartes’ (1641) claim that, the self essentially being athinking thing, we are conscious throughout sleep, and that this istrue even when upon awakening, we cannot remember any dreams (for ageneral introduction, see Olson 2010; Uzgalis 2014). This conceptionof dreamless sleep is deeply confused, according to Locke, because itthreatens to decouple conscious experience frommemory.Contra Descartes, he argues that

No man’s knowledge here, can go beyond hisexperience. Wake a man out of a sound sleep, and ask him, what he wasthat moment thinking on? If he himself be conscious of nothing he thenthought on, he must be a notable diviner of thoughts, that can assurehim, that he was thinking: may he not with more reason assure him, hewas not asleep? This is something beyond philosophy; and it cannot beless than revelation, that discovers to another, thoughts in my mind,when I can find none there myself […]. (Locke 1689: II.I.19)

By contrast, the proponent of the claim that weare conscious throughout sleep will have to additionally explain why,upon awakening, it does not always seem to us that we were, and whywe are only sometimes able to remember dreams. Locke’s denialof unrecalled (but nonetheless conscious) thinking throughout sleepis closely related to his claim that personal identity depends onpsychological continuity and memory rather than on unrecalled (butallegedly continuous and conscious) thinking. He invites us toimagine two men sharing one continuously thinking soul andalternating by turns between sleep and wakefulness (Locke 1689:II.I.12). He argues that if one man retained no memory of thesoul’s thoughts and perceptions while it was linked to theother man’s body, they would be distinct persons. Despite thecontinuous presence of thinking, psychological continuity would, inthis case, be violated.

Valberg points out that the dream argument, as raised in thecontext of Cartesian dream skepticism, raises a puzzle about therelation between the subject of the dream (i.e., the dream self) andthe sleeping subject who is the dreamer of the dream and who recallsthe dream upon awakening (Valberg 2007). He notes that there is nosimple way of making sense of the claim that it is I who emerge from adream or that I was the victim of deception in a givendream. Awakening involves a chasm, a transition between discreteworlds with discrete spaces and times. Here, it does not make sense tosay that “the ‘I’ at these times [is] a singleindividual who crosses from one world to the other” (Valberg2007: 69).

Vicarious dreams, or dreams in which the protagonist of the dreamis not continuous with the dreamer, are particularly puzzling withrespect to the identity of the dream self. They may even raise thequestion of whether the dream self has an independent existence (Rosen& Sutton 2013: 1047). While such dreams bear a superficialsimilarity to cases in which we imagine being another person, theycannot, according to Rosen and Sutton, be explained in the samemanner. They point out that imagining that one is another personinvolves a process of explicitly framing the imagined person’sthoughts as diverging from one’s own. Here, one retainsone’s own perspective in addition to the imagined one. Bycontrast, in nonlucid dreams, this type of explicit framing is missingand only the perspective of the dream’s protagonist isretained. For this reason, they take the analysis of perspective indreams and its comparison to perspective in imagination and memory tobe an important goal for future research.

Increasing attention has also been paid to the nature ofself-representation in dreams. Metzinger (2003, 2009, 2013b; see alsoWindt & Metzinger 2007) analyzes dreams in the context of theself-model theory of subjectivity. The key claim of the theory is thatno such thing as selves exist and that self-consciousness can beanalyzed as a particular type of representational content. The theoryintroduces a set of interdisciplinary constraints for describingself-consciousness and the first-person perspective on thephenomenological, representational, functional and neuroscientificlevels of description and attempts to accommodate a number ofneurophenomenological case studies. Dreaming plays an important rolein this context because in nonlucid dreams, according to Metzinger(2003, 2009), phenomenal selfhood is impoverished as compared tostandard wake states. Dreaming involves the experience of a self in aworld, but because of the cognitive and mnemonic deficiencies thatcharacterize nonlucid dreams (cf. Hobson et al. 2000), dreamers failto develop a stable first-person perspective and thephenomenal-functional property of agency is at best weaklyinstantiated. While dreamers can act upon desires or impulses, they donotexperience themselvesas a self in the act ofdeciding, attending or rationally thinking about certain events, andthey cannot ascribe this property to themselves. Also, because ofdream amnesia, dreams are only weakly integrated with theautobiographical self-model. Rather than being committed to a uniformcharacterization of phenomenal selfhood in dreams, the theory attemptsto accommodate a considerable degree of variability in phenomenalselfhood in dreaming (Windt & Metzinger 2007). In particular, itpredicts that lucidity results from a wake-like stabilization of thefirst-person perspective, enabling dreamers to not only experiencethemselves as the center of the dream world, but to form a stableconscious model (or what Metzinger 2003: 411–426 calls a“phenomenal model of the intentionality relation”) oftheir epistemic or agentive relation to the dream world and hence torealize that they are only dreaming.

While Descartes’ dream argument suggests that dreams simplyreplicate the phenomenology of selfhood that characterizes standardwake states (for a similar view, see Revonsuo 2005), the emergingpicture is that the phenomenology of selfhood is in fact more variablein dreams than commonly assumed. The analysis of phenomenal selfhoodin dreams may also shed light on different and potentially dissociabledimensions of self-consciousness. It has been suggested that preciselybecause important dimensions of phenomenal selfhood are missing indreams, the analysis of self-experience in dreams can help identifythe conditions for the emergence of minimal phenomenal selfhood, orthe simplest forms of self-consciousness (Blanke & Metzinger2009). Windt (2010; see also Metzinger 2013b) argues that in certaindreams, self-experience is reduced to purespatiotemporal-self-location arising independently of thephenomenology of embodied selfhood, suggesting that neither bodyownership nor the sense of agency are strictly necessary forself-consciousness. Moreover, if dreams can generally be described asinvolving the phenomenology of spatiotemporal self-location, thismight give rise to a new definition of dreams as immersivespatiotemporal hallucinations during sleep (Windt 2010).

5. Immorality and moral responsibility in dreams

The question of whether dreams are morally significant isimportantly related to the epistemological problem of whether I canrule out that I am now dreaming, but also to questions concerning thestatus of self-experience in dreams and the identity of the dreamself. Augustine (Confessions) thought that dreams are notonly subjectively indistinguishable from waking life, but also tookthem to be a cause of moral concern because of their vivid phenomenalcharacter. In theConfessions, he considers dreams in whichhe engages in sexual acts. What worries him is that these dream imagesare not faint, as in waking memory, but rather involve pleasure aswell as something resembling acquiescence or consent to the act. Hefamously concludes, however, that the moment of passing from sleep towakefulness, orvice versa, makes such a great differencethat he can return to a clear conscience upon awakening and restassured that he was not responsible for the acts performed in hisdreams.

Three types of arguments might support this conclusion (Matthews1981). The first is related to the familiar problem of the identity ofthe dream and waking self (for a general discussion on therelationship between personal identity and ethics, see Shoemaker2014): if the dream and waking self are not identical, then wakingAugustine is not morally responsible for dream-Augustine’sactions. Second, one might think that because the actions performed ina dream do not really happen, they are morally irrelevant. And third,assuming that moral responsibility requires the ability to actotherwise, dreams provide no grounds for moral concern because wecannot refrain from having certain types of dreams. Matthews (1981)argues, however, that none of these responses is available toAugustine. According to Matthews, Augustine believed that in hisdreams, he himself experienced genuine pleasure about and alsogenuinely consented to sexual activity. This rules out the first twoarguments, because Augustine also, according to Matthews, thoughtconsent and pleasure to be sufficient for moral responsibility even inthe absence of a corresponding physical action. Moreover, Augustineapparently believed that under certain conditions, he could refrainfrom sinful acts in his dreams, thus blocking the third.

Similar issues have also been raised by a number of otherauthors. Mullane (1965) takes up Freud’s observation that weoften do assume responsibility for the content of our dreams andargues that while we don’t have full control over our dreams,they are not completely involuntary either; rather, as is the case forblushing, considerable effort is required to attain control over ourdreams. This is supported by findings on lucid dreaming. While luciddreaming is a learnable skill, even practiced lucid dreamers are onlyrarely successful at controlling their dreams, and attempts at dreamcontrol often have unexpected results (Stumbrys et al. 2014). Mullane(1966) even argues that under certain conditions, dreams can beconsidered as actions; at least this question, according to Mullane,is a factual one and not a conceptual absurdity.

Taking lucid control dreams as one’s point of departure, thequestion of whether our dreams count as actions and whether this issufficient for moral responsibility may seem oversimplified, perhapsrequiring one answer for lucid dreams and another for nonlucid ones.This worry relates to the issue of whether we generally have controleven over our nonlucid dreams, as discussed in the context of theimagination view of dreaming. Here, a first question is whetherevidence on lucid control dreams provides sufficient grounds forclaiming that we have the same type of control over our nonluciddreams. A second question is whether we really have control even overour waking imaginings, as is widely accepted in the philosophicalliterature (seesection 2.6). Drawing fromresearch on mind wandering, Metzinger (2013a) has recently argued thatepisodes of mind wandering involve a cyclically recurring loss ofmental autonomy, or the ability to deliberately control one’sconscious thought processes. Consequently, they cannot properly beconsidered as mental actions, but rather should be regarded as a formof unintentional mental behavior. Moreover, because mind wanderingmakes up a large part of waking mental activity (Schooler etal. 2011), Metzinger argues that rational mental self-control is theexception rather than the rule. If this is correct, then similarissues about cognitive agency and moral responsibility can be raisedabout dreams and waking thought.

6. The meaning of dreams and the functions of dreaming

6.1 The meaning of dreams

Since antiquity, different ways of interpreting dreams have beenthe main source of interest for laypeople and psychologists discussingdreaming (Artemidorus’Interpretation of Dreams andFreudian dream theory are two particularly prominent examples).Historically, the epistemic status of dreams and the use of propheticand diagnostic dreams was not just a theoretical, but a practicalproblem (Barbera 2008). Different types of dreams were distinguishedby their putative epistemic value. Artemidorus, for instance, used thetermenhypnion to refer to dreams that merely reflect thesleeper’s current bodily or psychological state and hence do notmerit further interpretation, whereas he reserved thetermoneiron for meaningful and symbolic dreams of divineorigin.

The practice of dream interpretation was famously attacked byAristotle inOn Prophecy in Sleep. Here, he sharplycriticizes the idea that dreams are of divine origin, but allows thatoccasionally, diagnostic or even prophetic dreams are caused by smallaffections, which are drowned out in wakefulness and have a morepronounced effect during the quiet of sleep, thus enabling the sleeperto perceive distant events. He adds, however, that such dreams occurmostly in dullards whose minds resemble an empty desert, thusrendering them more susceptible to the subtle movements of theperceptual organs during sleep. As Kroker (2007: 37) points out, thisremark was not apt to encourage people to pay greater attention totheir dreams. It is thus somewhat ironic that the earliest knownsystematic account of dreaming also encouraged the view that dreams,as occurrences in sleep, are unobservable and hence not a serioustarget of scientific research. Later philosophers went even further,typically regarding dreams, if not as a source of deception inDescartes’ sense, then as a source of superstitious beliefs(Hobbes 1651; Kant 1766; Schopenhauer 1847).

In the context of Freudian dream theory, dream interpretation oncemore takes a prominent role as the royal road to knowledge of theunconscious mind, and again, this is associated with claims about thepsychic (as opposed to external or bodily:cf.section 2.5) sources of dreaming.

What we see, then, is that views on the epistemic status of dreamsand the type of knowledge (e.g., knowledge about the future, diagnosisof physical ailments, or insights about one’s current concerns)dreams purportedly give rise to changed in tandem with views on theorigin of dreaming, which were gradually relocated from divine originsand external sources, via the body, to the unconscious as in Freudiandream theory or the brain as in contemporary theories of dreaming.

Finally, it is important to note that the claim that dreams atleast occasionally give rise to personal insights is not sufficientfor saying that dreams are intrinsically meaningful or have a hiddenmeaning requiring special methods of interpretation. Hobson famouslyargues that dreams are the product of the random, brain-stem drivenactivation of the brain during sleep (Hobson 1988) and at best enablepersonal insight in the manner of a Rorschach test (Hobson etal. 2000; Metzinger 2003). A similar account is suggested by Dennett.He notes that even granting that dreams—or rather: dreamreports—occasionally have seemingly symbolic content andnarrative structure, this does not show them to be the product ofauthorial intentions. InConsciousness Explained (1991),Dennett introduces the “party game of psychoanalysis” tocompare the production of dream narratives to a mindless, aimless gameof question-and-answer, governed by simple rules. The point is thatdreams might seem highly symbolic and meaningful without thereby beingthe product of intelligent and deliberate narrative processes (seeMcGinn 2004 for a defense of the contradictory view that dreams bearthe marks of intelligent design). Dennett’s account also sitswell with newer accounts involving predictive processing andhypothesis testing (seesection3.1). Finally, even if Hobson’s and Dennett’s accountsare successful in undermining the claim that dreams are inherentlymeaningful (in the sense of being messages, perhaps, from theunconscious, as in Freudian dream theory), it might still be the casethat in certain settings and using certain methods, dreaminterpretation can be a personally meaningful source of insight andcreativity, and Hobson himself has defended such a view (Hobson &Wohl 2005). Whether dream interpretation is a source of insight is atleast in part an empirical question that is only beginning to beinvestigated systematically (see Edwards et al. 2013 for a recentreview of the empirical literature and preliminary evidence supportingthis claim).

6.2 The functions of dreaming

Asking about the epistemic status of dreams is importantlydifferent from asking about the evolutionary functions ofdreaming. Many different theories of the functions of dreaming havebeen proposed and the debate is still very much ongoing. A firstimportant distinction is the one between the functions of thedifferent stages of sleep and the functions ofdreaming. Well-documented functions of REM sleep includethermoregulation and the development of cortical structures in birdsand mammals, as well as neurotransmitter repletion, the reconstructionand maintenance of little-used brain circuits, the structuraldevelopment of the brain in early developmental phases, as well as thepreparation of a repertoire of reflexive or instinctive behaviors(Hobson 2009). According to protoconsciousness theory, REM sleep playsan important role in foetal development by providing a virtual worldmodeleven before full-blown consciousness isdeveloped (Hobson 2009: 808).

Numerous studies have investigated the contribution of sleep tomemory consolidation, with different sleep stages apparently promotingdifferent types of memories (Diekelmann et al. 2009; Walker2009). However, only a few studies have investigated the relationshipbetween dream content and memory consolidation in sleep (for anoverview, see Nielsen & Stenstrom 2005). While dreams rarelyinvolve episodic replay of waking memories (Fosse et al. 2003), thereis preliminary evidence suggesting that performance in a virtualnavigation task improves following daytime naps, and that the effectis especially strong in subjects who report task-related mentation(Wamsley & Stickgold 2009, 2010; Wamsley et al. 2010).

It is also important to note that different theories on thefunctions of dreaming may be more or less tailored to certain types ofdreams. Two prominent theories focus on bad dreams and nightmares. Ithas long been thought that dreaming contributes to emotionalprocessing and that this is particularly obvious in the dreams ofnightmare sufferers or in dreams following traumatic experiences(e.g., Hartmann 1998; Nielsen & Lara-Carrasco 2007; Levin &Nielsen 2009; Cartwright 2010; Perogamvros et al. 2013). Based on thehigh prevalence of negative emotions and threatening dream content,the threat simulation theory suggests that the evolutionary functionof dreaming lies in the simulation of ancestral threats and that therehearsal of threatening events and avoidance skills in dreams has anadaptive value by enhancing the individual’s chances of survival(see Revonsuo 2000; Valli 2008).

Finally, even if dreaming and general, and specific types of dreamcontent in particular, were found to be strongly associated withparticular cognitive functions, it would still be possible that dreamsare mere epiphenomena of the periodic activation of the brain duringsleep. They might, as (Flanagan 1995, 2000) puts it, be the spandrelsof sleep. Yet, this would not prevent them from serving a derivativepsychological function and from being personally meaningfulexperiences.

A particular problem for any theory on the function of dreaming isto explain why a majority of dreams are forgotten and how dreams canfulfill their putative function independently of recall. Crick andMitchinson (1983) famously proposed that REM sleep“erases” or deletes surplus information and unnecessarymemories, which, if true, would suggest that enhanced dream recallmight actually undermine the effectiveness of the memory-erasingsystem. Another problem is that the ability to recall, and perhapseven to experience, dreams can be lost selectively and independentlyof other cognitive deficits (Solms 1997, 2000). This suggests that itis at least as important to understand which cognitive functions areindependent of dreaming as to understand those that are not.

An evolutionary perspective can also be fruitfully applied to thespecific phenomenology of dreaming. According to thevigilancehypothesis, natural selection disfavored the occurrence of thosetypes of sensations during sleep that would compromise vigilance(Symons 1993). Hallucinatory sounds, but also smells or pains would,according to Symons, distract attention from the potentiallydangerous surroundings of the sleeping subject. Consequently, thevigilance hypothesis predicts that they only rarely occur in dreamswithout causing awakening. By contrast, because most mammals sleepwith their eyes closed and in an immobile position, vivid visual andmovement hallucinations during sleep do not comprise vigilance andthus can occur in dreams without endangering the sleeping subject. Ifthis is correct, then focusing on the stuff dreams arenotmade of may be at least as important for understanding the function ofdreaming as developing a positive account.

7. Conclusions

Throughout this entry, it has become clear that there is anintimate connection among the questions asked about dreaming indifferent areas of philosophy such as epistemology, philosophy ofmind, and ethics. But it has also become clear that scientificevidence from sleep and dream research can meaningfully inform the philosophical discussion, and that it has often done so in the history of philosophical theorizing about dreaming. It is animportant constraint on any philosophical theory ofdreaming—insofar as it takes itself to be applicable toreal-world dreams—that it also be empirically plausible. Thoughthis point has sometimes been outright denied (e.g., Malcolm 1956, 1959), ithas increasingly come to be accepted by contemporary philosophersworking on dreams. An important perspective for the future is thataside from being empirically informed, philosophical theories ofdreaming should also strive to beempiricallyinformative—for instance by clarifying the precise rolethat dreaming can play in the context of general theories ofconsciousness and subjectivity and by suggesting specific contrastconditions, such as the contrast between dreams and waking mindwandering, delusions, and hallucinations. Further integrating thefields of philosophy of mind and philosophy of cognitive science withscientific sleep and dream research consequently is an important goalfor the future.

Bibliography

• Aleman, A. and F. Larøi, 2008,Hallucinations: TheScience of Idiosyncratic Perception, Washington, DC: AmericanPsychological Association.
• Antrobus, J.S., 1990, “The Neurocognition of SleepMentation: Rapid Eye Movements, Visual Imagery, and Dreaming”,inSleep and Cognition, R. Bootzin, J. Kihlstrom, andD. Schacter (eds.), Washington: American Psychological Association,pp. 3–24.
• Aristotle,On Dreams, in Aristotle:On theSoul. Parva Naturalia. On Breath, (Loeb Classical LibraryNo. 288), W.S. Hett (ed.), Cambridge, MA & London: HarvardUniversity Press, 1986.
• –––,On Prophecy in Sleep, inAristotle:On the Soul. Parva Naturalia. On Breath, (LoebClassical Library No. 288), W.S. Hett (ed.), Cambridge, MA &London: Harvard University Press, 1986.
• –––,On Sleeping and Waking, inAristotle:On the Soul. Parva Naturalia. On Breath, (LoebClassical Library No. 288), W.S. Hett (ed.), Cambridge, MA &London: Harvard University Press, 1986.
• Artemidorus,The Interpretation of Dreams, R.J. White(ed.), New Jersey: Noyes Press, 1975.
• Aserinsky, E. and N. Kleitman, 1953, “Regularly OccurringPeriods of Eye Motility and Concurrent Phenomena duringSleep”,Sleep Medicine Review, 118: 273–274.
• –––, 1955, “Two Types of Ocular MotilityOccurring in Sleep”,Journal of Applied Physiology, 8:1–10.
• Augustine,Against the Academics, J.J. O'Meara (ed.),Westminster, MD: Newman Press, 1950.
• –––,Confessions, H. Chadwick (ed.),Oxford: Oxford University Press, 1991.
• Austin, J.L., 1962,Sense and Sensibilia, G.J. Warnock(ed.), Oxford & New York: Oxford University Press.
• Ayer, A.J., 1960, “Professor Malcolm onDreams”,Journal of Philosophy, 57: 517–535.
• Baillet, A., 1691,La Vie de Monsieur Descartes, Paris:La Table Ronde.
• Baldridge, B.J., 1966, “Physical Concomittants of Dreamingand the Effect of Stimulation on Dreams”,Ohio State MedicalJournal, 62: 1272–1275.
• Barbera, J., 2008, “Sleep and Dreaming in Greek and RomanPhilosophy”,Sleep Medicine, 9: 906–910.
• Barrett, D. and P. McNamara (eds.), 2007a,The New Science ofDreaming, Volume 1: Biological Aspects, Westport: PraegerPerspectives.
• ––– (eds.), 2007b,The New Science ofDreaming, Volume 2: Content, Recall, Personality Correlates,Westport: Praeger Perspectives.
• ––– (eds.), 2007c,The New Science ofDreaming, Volume 3: Cultural and Theoretical Perspectives,Westport: Praeger Perspectives.
• Bayne, T.J. and E. Pacherie, 2005, “In Defence of theDoxastic Conception of Delusions”,Mind and Language,20(2): 163–188.
• Berger, R.J., 1963, “Experimental Modification of DreamContent by Meaningful Verbal Stimuli”,British Journal ofPsychiatry, 109: 722–740.
• Bergson, H., 1914,Dreams, E.E. Slosson (ed. andtrans.), New York: B.W. Huebsch.[Bergson 1914 available online]
• Berkeley, G., 1710, “A Treatise Concerning the Principlesof Human Knowledge”, inPrinciples of Human Knowledge andThree Dialogues, H. Robinson (ed.), Oxford: Oxford UniversityPress, pp. 1–96.
• Binz, C., 1878,Über den Traum, Bonn: AdolphMarcus.
• Blagrove, M., L. Farmer, and E. Williams, 2004, “TheRelationship of Nightmare Frequency and Nightmare Distress toWell-Being”,Journal of Sleep Research, 13:129–136.
• Blanke, O. and T. Metzinger, 2009, “Full-Body Illusions andMinimal Phenomenal Selfhood”,Trends in CognitiveSciences, 13(1): 7–13.
• Block, N., 2007, “Consciousness, Accessibility, and theMesh between Psychology and Neuroscience”,Behavioral andBrain Sciences, 30: 499–548.
• Bortolotti, L., 2009,Delusions and Other IrrationalBeliefs, Oxford: Oxford University Press.
• –––, 2013, “Delusion”,TheStanford Encyclopedia of Philosophy (Winter 2013 Edition),E.N. Zalta (ed.), URL =<https://plato.stanford.edu/archives/win2013/entries/delusion/>.
• Bostrom, N., 2003, “Are We Living in a ComputerSimulation?”,The Philosophical Quarterly, 53(211):243–255.
• Bourdin, P., 1641, “Seventh Set of Objections”,reprinted in Moriarty 2008: 214–231.
• Bradley, F.H., 1894, “The Failure of Movement inDream”,Mind, 3(11): 373–377.
• Breger, L., I. Hunter, and R.W. Lane, 1971,The Effect ofStress on Dreams, New York: International UniversitiesPress.
• Broughton, J., 2002,Descartes's Method of Doubt,Princeton & Oxford: Princeton University Press.
• –––, 2006, “Impressions and Ideas”,inThe Blackwell Guide to Hume's Treatise, S. Traiger (ed.),Malden, MA & Oxford: Blackwell, pp. 43–57.
• Browne, A., 1977, “Descartes's Dreams”,Journalof the Warburg and Courtauld Institutes, 40: 256–273.
• Brueckner, T., 2012, “Skepticism and ContentExternalism”,The Stanford Encyclopedia of Philosophy(Spring 2012 Edition), E.N. Zalta (ed.), URL =<https://plato.stanford.edu/archives/spr2012/entries/skepticism-content-externalism/>.
• Canfield, J.V., 1961, “Judgments in Sleep”,ThePhilosophical Review, 70: 224–230.
• Cartwright, R.D., 2010,The Twenty-four Hour Mind: The Roleof Sleep and Dreaming in our Emotional Lives, Oxford: OxfordUniversity Press.
• Chalmers, D.J., 2005, “The Matrix as Metaphysics”, inGrau 2005: 132–176.
• Chappell, T., 2013, “Plato on Knowledge intheTheaetetus”,The Stanford Encyclopedia ofPhilosophy (Winter 2013 Edition), E.N. Zalta (ed.), URL =<https://plato.stanford.edu/archives/win2013/entries/plato-theaetetus/>.
• Chihara, C.S., 1965, “What Dreams Are MadeOn”,Theoria, 31: 145–158.
• Chihara, C.S. and J.A. Fodor, 1965, “Operationalism andOrdinary Language: A Critique of Wittgenstein”,AmericanPhilosophical Quarterly 2: 281–295; page reference is tothe reprint in Dunlop 1977.
• Churchland, P.S., 1988, “Reduction and the NeurobiologicalBasis of Consciousness”, inConsciousness in ContemporaryScience, A. Marcel and E. Bisiach (eds.), Oxford: OxfordUniversity Press, pp. 273–304.
• Clark, A., 2005, “The Twisted Matrix: Dream, Simulation, orHybrid?”, in Grau 2005: 177–197.
• –––, 2013a, “Dreaming the Whole Cat:Generative Models, Predictive Processing, and the EnactivistConception of Perceptual Experience”,Mind, 121(483),753–771.
• –––, 2013b, “Whatever Next? PredictiveBrains, Situated Agents, and the Future of CognitiveScience”,Behavioral and Brain Sciences, 36(03),181–204.
• Clarke, D.M., 2006,Descartes: A Biography, Cambridge& New York: Cambridge University Press.
• Cohen, M.A. and D.C. Dennett, 2011, “Consciousness CannotBe Separated from Function”,Trends in CognitiveSciences, 15(8), 358–364.
• Cole, J.R., 1992,The Olympian Dreams and Youthful Rebellionof René Descartes, Urbana & Chicago: University ofIllinois Press.
• Conrad, T., 1968,Zur Wesenslehre des psychischen Lebens undErlebens, (Phaenomenologica: Vol. 27), DenHaag: Nijhoff.
• Crane, T., 2011, “The Problem of Perception”,TheStanford Encyclopedia of Philosophy (Spring 2011 Edition),E.N. Zalta (ed.), URL =<https://plato.stanford.edu/archives/spr2011/entries/perception-problem/>.
• Crick, F. and G. Mitchinson, 1983, “The Function of DreamSleep”,Nature, 304, 111–114.
• Currie, G., 2000, “Imagination, Delusion andHallucination”,Mind & Language, 15(1),168–183.
• Currie, G. and I. Ravenscroft, 2002,Recreative Minds:Imagination in Philosophy and Psychology, Oxford: ClarendonPress.
• D’Agostino, A., A. Castelnovo, and S. Scarone, 2013,“Dreaming and the Neurobiology of Self: Recent Advances andImplications for Psychiatry”,Frontiers in Psychology,4, doi:10.3389/fpsyg.2013.00680 [available online]
• Dang-Vu, T.T., M. Schabus, M. Desseilles, S. Schwartz,P. Maquet, 2007, “Neuroimaging of Sleep and Dreaming”, inBarrett and McNamara 2007a: 95–114.
• Dement, W.C., 1999,The Promise of Sleep. The ScientificConnection between Health, Happiness and a Good Night’sSleep, London: Pan Books.
• Dement, W.C. and N. Kleitman, 1957, “The Relation of EyeMovements during Sleep to Dream Activity: An Objective Method for theStudy of Dreaming”,Journal of Experimental Psychology,53: 89–97.
• Dement, W.C. and E. Wolpert, 1958, “The Relation of EyeMovements, Body Motility, and External Stimuli to DreamContent”,Journal of Experimental Psychology, 55:543–553.
• Dennett, D.C., 1976, “Are dreamsexperiences?”,The Philosophical Review, 85(2):151–171.
• –––, 1979, “The Onus Re Experiences: AReply to Emmett”,Philosophical Studies, 35(April):315–318.
• –––, 1991,ConsciousnessExplained. Boston, New York & London: Little, Brown andCompany.
• Descartes, R., 1637,Discourse on the Method of RightlyConducting the Reason, and Seeking Truth in the Sciences.,G.B. Rawlings(ed.). [Descartes 1637 available online]
• –––, 1641,Meditations on FirstPhilosophy, reprinted in Moriarty 2008: 1–64.
• Desseilles, M., T.T. Dang-Vu, V. Sterpenich, and S. Schwartz,2011, “Cognitive and Emotional Processes during Dreaming: ANeuroimaging View”,Consciousness and Cognition, 20(4):998–1008.
• Diekelmann, S., I. Wilhelm, and J. Born, 2009, “The Whatsand Whens of Sleep-Dependent Memory Consolidation”,SleepMedicine Reviews, 13(5): 309–321.
• Diogenes Laertius,Lives of Eminent Philosophers,R.D. Hicks (ed.), Cambridge MA: Harvard University Press, 1943.
• Domhoff, G.W., 2001, “A New Neurocognitive Theory ofDreams”,Dreaming, 11: 13–33.
• –––, 2003,The Scientific Study of Dreams:Neural Networks, Cognitive Development, and Content Analysis,Washington, DC: American Psychological Association.
• –––, 2011, “The Neural Substrate forDreaming: Is It a Subsystem of the DefaultNetwork?”,Consciousness and Cognition, 20(4):1163–1174.
• Downing, L., 2013, “George Berkeley”,TheStanford Encyclopedia of Philosophy (Spring 2013 Edition),E.N. Zalta (ed.), URL =<https://plato.stanford.edu/archives/spr2013/entries/berkeley/>.
• Dreisbach, C., 2000, “Dreams in the History ofPhilosophy”,Dreaming, 10(1): 31–41.
• Dresler, M., S.P. Koch, R. Wehrle, V.I. Spoormaker, F. Holsboer,A. Steiger, P. Sämann, H. Obrig, and M. Czisch, 2011,“Dreamed Movement Elicits Activation in the SensorimotorCortex”,Current Biology, 21(21): 1833–1837.
• Dresler, M., R. Wehrle, V.I. Spoormaker, S.P. Koch, F. Holsboer,A. Steiger, H. Obrig, P. Sämann, and M. Czisch, 2012,“Neural Correlates of Dream Lucidity Obtained from ContrastingLucid versus Non-lucid REM Sleep: A Combined EEG/fMRI CaseStudy”,Sleep, 35(7): 1017–1020.
• Dunlop, C.E.M. (ed.), 1977,Philosophical Essays onDreaming. Ithaca & London: Cornell University Press.
• Edwards, C.L., P.M. Ruby, J.E. Malinowski, P.D. Bennett, andM.T. Blagrove, 2013, “Dreaming and Insight”,Frontiersin Psychology, 4, doi:10.3389/fpsyg.2013.00979[available online]
• Eichenlaub, J.-B., O. Bertrand, D. Morlet, and P. Ruby, 2013,“Brain Reactivity Differentiates Subjects with High and LowDream Recall Frequencies during Both Sleep andWakefulness”,Cerebral Cortex, 2:1–10.
• Ellis, H., 1911,The World of Dreams, London: Constable& Company LTD.
• Emmett, K., 1978, “OneiricExperiences”,Philosophical Studies, 34(November):445–450.
• Erlacher, D., M. Schredl, and S. LaBerge, S., 2003, “MotorArea Activation during Dreamed Hand Clenching: A Pilot Study on EEGAlpha Band”,Sleep and Hypnosis, 5: 182–187.
• Erlacher, D., M. Schädlich, T. Stumbrys, and M. Schredl,2014, “Time for Actions in Lucid Dreams: Effects of TaskModality, Length, and Complexity”,Frontiers inPsychology, 4, doi:10.3389/fpsyg.2013.01013[available online]
• ffytche, D.H., 2007, “Visual Hallucinatory Syndromes: Past,Present, and Future”,Dialogues in ClinicalNeuroscience, 9(2): 173–189.
• ffytche, D.H., J.D. Blom, and M. Catani, 2010, “Disordersof Visual Perception”,Journal of Neurology, Neurosurgery& Psychiatry, 81(11): 1280–1287.
• Flanagan, O., 1995, “Deconstructing Dreams: The Spandrelsof Sleep”,The Journal of Philosophy, 92:5–27.
• –––, 2000,Dreaming Souls: Sleep, Dreams,and the Evolution of the Conscious Mind, Oxford & New York:Oxford University Press.
• Fletcher, P.C. and C.D. Frith, 2008, “Perceiving isBelieving: A Bayesian Approach to Explaining the Positive Symptoms ofSchizophrenia”,Nature Reviews Neuroscience, 10(1):48–58.
• Fosse, M.J., R. Fosse, J.A. Hobson, and R.J. Stickgold, 2003,“Dreaming and Episodic Memory: A FunctionalDissociation?”,Journal of Cognitive Neuroscience, 15:1–9.
• Foulkes, D., 1978,A Grammar of Dreams, New York: BasicBooks.
• –––, 1993a, “Children’sDreaming”, inDreaming as Cognition, C. Cavallero andD. Foulkes (eds.), New York: Harvester Wheatsheaf,pp. 114–132.
• –––, 1993b, “Dreaming and REMSleep”,Journal of Sleep Research,2:199–202.
• –––, 1999,Children’s Dreaming and theDevelopment of Consciousness, Cambridge, MA and London: HarvardUniversity Press.
• Fox, K.C.R., S. Nijeboer, E. Solomonova, G.W. Domhoff, andK. Christoff, 2013, “Dreaming as Mind Wandering: Evidence fromFunctional Neuroimaging and First-Person ContentReports”,Frontiers in Human Neuroscience, 7,doi:10.3389/fnhum.2013.00412 [available online]
• Frankfurt, H.G., 1970,Demons, Dreamers, and Madmen: TheDefense of Reason in Descartes's Meditations, Princeton &Oxford: Princeton University Press.
• Freud, S., 1899,Die Traumdeutung, Frankfurt am Main:Fischer Taschenbuch Verlag (2003).
• –––, 1940,Schriften über Träumeund Traumdeutungen, Frankfurt am Main: Fischer Taschenbuch Verlag(2003).
• Galen,On Diagnosis in Dreams, L. Pearcy (ed.),<available online>.
• Gendler, T., 2013, “Imagination”,The StanfordEncyclopedia of Philosophy (Fall 2013 Edition), E.N. Zalta (ed.),URL = <https://plato.stanford.edu/archives/fall2013/entries/imagination/>.
• Germain, A. and A. Zadra, 2009, “Dreams and Nightmares inPTSD”, in Stickgold and Walker 2009: 316–322.
• Gerrans, P., 2012, “Dream Experience and a RevisionistAccount of Delusions of Misidentification”,Consciousnessand Cognition, 21(1): 217–227.
• –––, 2013, “Delusional Attitudes andDefault Thinking”,Mind & Language, 28(1):83–102.
• –––, 2014, “Pathologies ofHyperfamiliarity in Dreams, Delusions and DéjàVu”,Frontiers in Psychology, 5,doi:10.3389/fpsyg.2014.00097[available online]
• Globus, G.G., 1987,Dream Life, Wake Life: The HumanCondition Through Dreams, New York: State University of New YorkPress.
• Goblot, 1896, “Sur le souvenir desrêves”,Revue philosophique,XLII.
• Gottesmann, C., 2006, “The Dreaming Sleep Stage: A NewNeurobiological Model of Schizophrenia?”,Neuroscience,140: 1105–1115.
• Grau, C. (ed.), 2005,Philosophers Explore the Matrix,C. Grau (ed.), Oxford: Oxford University Press.
• Gregory, J.C., 1916, “Dreams as PsychicalExplosions”,Mind, 25(98): 193–205.
• –––, 1918, “The Dream of ‘FrustratedEffort’: A Suggested Explanation”,Mind, 27(105):125–128.
• Grundmann, T., 2002, “Die Struktur des skeptischenTraumarguments”,Grazer Philosophische Studien, 64:57–81.
• Hacking, I., 2001, “Dreams in Place”,Journal ofAesthetics and Art Criticism, 59(3):244–260.
• Hall, C.S., 1981, “Do We Dream during Sleep? Evidence forthe Globot Hypothesis”,Perceptual and Motor Skills,53(1): 239–246.
• Hartmann, E., 1998,Dreams and Nightmares: The New Theory onthe Origin and Meaning of Dreams, Cambridge: Perseus Books.
• Hearne, K., 1978,Lucid Dreams: An Electro-Physiological andPsychological Study, (Ph.D. thesis), University of Liverpool,England. [Hearne 1978 available online]
• Hering, J., 1947, “Concerning Image, Idea, andDream”,Philosophy and Phenomenological Research, 8(2):188–205.
• Hobbes, T., 1651,Leviathan, C.B. Macpherson (ed.),London: Penguin (1985).
• –––, 1641, “Third Set ofObjections”, reprinted in Moriarty 2008: 107–124.
• Hobson, J.A., 1988,The Dreaming Brain, New York: BasicBooks.
• –––, 1999,Dreaming as Delirium. How theBrain Goes Out of Its Mind, Cambridge MA: MIT Press.
• –––, 2009, “REM Sleep and Dreaming:Towards a Theory of Protoconsciousness”,Nature ReviewsNeuroscience, 10(November): 803–813.
• Hobson, J. and K. Friston, 2012, “Waking and DreamingConsciousness: Neurobiological and FunctionalConsiderations”,Progress in Neurobiology, 98(1):82–98.
• Hobson, J., E.F. Pace-Schott, and R. Stickgold, 2000,“Dreaming and the Brain. Toward a Cognitive Neuroscience ofConscious States”,Behavioral and Brain Sciences, 23:793–842.
• Hobson, J. and H. Wohl, 2005,From Angels to Neurones. Artand the New Science of Dreaming, Parma: Mattioli 1885.
• Hodges, M. and W.R. Carter, 1969, “Nelson on Dreaming aPain”,Philosophical Studies, 20(3): 43–46.
• Hoelscher, T.J., E. Klinger, and S.G. Barta, 1981,“Incorporation of Concern- and Nonconcern-related Verbal Stimuliinto Dream Content”,Journal of Abnormal Psychology,90: 88–91.
• Hohwy, J., 2013,The Predictive Mind, Oxford: OxfordUniversity Press.
• Horikawa, T., M. Tamaki, Y. Miyawaki, and Y. Kamitani, 2013,“Neural Decoding of Visual Imagery duringSleep”,Science 340(6132): 639–642.
• Hoss, R.J., 2010, “Content Analysis on the PotentialSignificance of Color in Dreams: A PreliminaryInvestigation”,International Journal of DreamResearch, 3(1): 80–90.
• Huemer, M., 2011, “Sense-Data”,The StanfordEncyclopedia of Philosophy (Spring 2011 Edition), E.N. Zalta(ed.), URL =<https://plato.stanford.edu/archives/spr2011/entries/sense-data/>.
• Hume, D., 1739,A Treatise of Human Nature, D.F. Norton,M.J. Norton (eds.), Oxford & New York: Oxford University Press(2000).
• Hurlburt, R.T. and E. Schwitzgebel, 2007,Describing InnerExperience?: Proponent Meets Skeptic, Cambridge, MA & London:MIT Press.
• Husserl, E., 1904/1905,Phantasie undBildbewußtsein, E. Marbach (ed.), Hamburg: Felix Meiner(2006).
• Ichikawa, J., 2008, “Scepticism and the Imagination Modelof Dreaming”,The Philosophical Quarterly, 58(232):519–527.
• –––, 2009, “Dreaming andImagination”,Mind & Language, 24(1):103–121.
• James, W., 1890,The Principles of Psychology, VolumeTwo, New York: Dover Publications (1950).
• Jouvet, M., 1999,The Paradox of Sleep: The Story ofDreaming, L. Garey (ed.), Cambridge & London: MIT Press.
• Kahn, D., E.F. Pace-Schott, and J.A. Hobson, 2002, “Emotionand Cognition: Feeling and Character Identification inDreaming”,Consciousness and Cognition, 11:34–50.
• Kahn, D., R. Stickgold, E.F. Pace-Schott, and J.A. Hobson, 2000,“Dreaming and Waking Consciousness: A Character RecognitionStudy”,Journal of Sleep Research, 9:317–325.
• Kant, I., 1766,Träume eines Geistersehers,erläutert durch Träume der Metaphysik, Stuttgart:Reclam (2002).
• Kantor, J., 1970, “Pinching andDreaming”,Philosophical Studies, 21(1–2):28–32.
• Keefer, M.H., 1996, “The Dreamer’s Path: Descartesand the Sixteenth Century”,Renaissance Quarterly,49(1): 30–76.
• Klein, P., 2014, “Skepticism”,The StanfordEncyclopedia of Philosophy (Summer 2014 Edition), E.N. Zalta(ed.), URL =<https://plato.stanford.edu/archives/sum2014/entries/skepticism/>.
• Koulack, D., 1969, “Effects of Somatosensory Stimulation onDream Content”,Archives of General Psychiatry, (20):718–725.
• Kramer, M., 2007,The Dream Experience: A SystematicExploration, New York & London: Routledge.
• Kroker, K., 2007,The Sleep of Others and the Transformationsof Sleep Research, Toronto: University of Toronto Press.
• LaBerge, S., 2007, “Lucid Dreaming”, in Barrett andMcNamara 2007a: 307–328.
• LaBerge, S., L.E. Nagel, W.C. Dement, and V.P. Zarcone, 1981,“Lucid Dreaming Verified by Volitional Communication during REMSleep”,Perceptual and Motor Skills, 52:727–732.
• Leclair-Visonneau, L., D. Oudiette, B. Gaymard,S. Leu-Semenescu, and I. Arnulf, 2010, “Do the Eyes Scan DreamImages during Rapid Eye Movement Sleep? Evidence from the Rapid EyeMovement Sleep Behaviour Disorder Model”,Brain,133(6): 1737–1746.
• Leibniz, G.W., 1880,Die Philosophischen Schriften,Berlin: Weidmannsche Buchhandlung.
• –––,Philosophical Papers and Letters,L.E. Loemker (ed.), Chicago: University of Chicago Press (1956).
• Levin, R. and T.A. Nielsen, 2009, “Nightmares, Bad Dreams,and Emotions Dysregulation: A Review and New Neurocognitive Model ofDreaming”,Current Directions in Psychological Science,18(2): 84–88.
• Lewis, H.D., 1969,The Elusive Mind, London: GeorgeAllan & Unwin LTD.
• Limosani, I., A. D’Agostino, M.L. Manzone, and S. Scarone,2011a, “The Dreaming Brain/Mind, Consciousness andPsychosis”,Consciousness & Cognition, 20(4):987–992.
• –––, 2011b, “Bizarreness in Dream Reportsand Waking Fantasies of Psychotic, Schizophrenic and Manic Patients:Empirical Evidences and TheoreticalConsequences”,Psychiatry Research, 189(2):195–199.
• Llinás, R. and D. Paré, 1991, “Of Dreamingand Wakefulness”,Neuroscience, 44: 521–535.
• Llinás, R. and U. Ribary, 1994, “Perception as anOneiric-like State Modulated by the Senses”, inLarge-ScaleNeuronal Theories of the Brain, C. Koch and J. Davis (eds.),Cambridge, MA: MIT Press, pp. 111–124.
• Locke, J., 1689,An Essay Concerning HumanUnderstanding, R. Woolhouse (ed.), London: Penguin (1997).
• Macnish, R., 1838,The Philosophy of Sleep, Glasgow:W.R. M'Phun.
• Macpherson, F., 2013, “The Philosophy and Psychology ofHallucination: An Introduction”,inHallucination. Philosophy and Psychology, F. Macphersonand D. Platchias (eds.), Cambridge MA: MIT Press, pp. 1–38.
• Malcolm, N., 1956, “Dreaming and Skepticism”,ThePhilosophical Review, 65(1): 14–37.
• –––, 1959,Dreaming, London: Routledge& Kegan Paul.
• Matthews, G.B., 1981, “On Being Immoral in aDream”,Philosophy, 56(January): 47–64.
• –––, 2005,Augustine, Malden, MA:Blackwell Pub.
• Maury, L.-F. A., 1861,Le sommeil et les rêves:études psychologiques sur ces phénomènes et lesdivers états qui s'y rattachent, Paris: Didier et CieLibraires-Éditeurs.
• McGinn, C., 2004,Mindsight: Image, Dream, Meaning,Cambridge, MA & London: Harvard University Press.
• –––, 2005a, “The Matrix of Dreams”,in Grau 2005: 62–70.
• –––, 2005b,The Power of Movies: How Screenand Mind Interact, New York: Vintage Books.
• Merritt, J.M., R. Stickgold, E.F. Pace-Schott, J. Williams, andJ.A. Hobson, 1994, “Emotion Profiles in the Dreams of Men andWomen”,Consciousness and Cognition, 3:46–60.
• Metzinger, T., 2003,Being No One: The Self-Model Theory ofSubjectivity, Cambridge, MA & London: MIT Press.
• –––, 2009,The Ego Tunnel: The Science ofthe Mind and the Myth of the Self, New York: Basic Books.
• –––, 2013a, “The Myth of Cognitive Agency:Subpersonal Thinking as a Cyclically Recurring Loss of MentalAutonomy”,Frontiers in Psychology, 4,doi:10.3389/fpsyg.2013.00931[available online]
• –––, 2013b, “Why Are Dreams Interestingfor Philosophers? The Example of Minimal Phenomenal Selfhood, Plus anAgenda for Future Research”,Frontiers in Psychology,4, doi:10.3389/fpsyg.2013.00746[available online]
• Montaigne, M. de, “The Apology for Raymond Sebond”,inReadings in the History of Philosophy, R.M. Popkin(ed.),The Philosophy of the 16th and 17th Centuries,Toronto: Collier-Macmillan (1966): 70–81.
• Moriarty, M. (ed.), 2008,Meditations,Objections, and Replies, Oxford: Oxford University Press.
• Mullane, H., 1965, “Moral Responsibility forDreams”,Dialogue, 4(02): 224–229.
• –––, 1966, “Dreaming as anAction”,Dialogue, 5(02): 239–242.
• Murzyn, E., 2008, “Do We Only Dream in Colour? A Comparisonof Reported Dream Colour in Younger and Older Adults with DifferentExperiences of Black and White Media”,Consciousness andCognition, 17: 1228–1237.
• Nagel, T., 1959, “Dreaming”,Analysis,19(5): 112–116.
• –––, 1974, “What Is It Like to Be aBat?”,Philosophical Review, 83:435–450.
• Nelson, J.O., 1966, “Can One Tell that He is Awake byPinching Himself?”,Philosophical Studies, 17(6):81–84.
• Newman, L., 2010, “Descartes' Epistemology”,TheStanford Encyclopedia of Philosophy (Fall 2010 Edition),E.N. Zalta (ed.), URL =<https://plato.stanford.edu/archives/fall2010/entries/descartes-epistemology/>.
• Nielsen, T.A., 2000, “A Review of Mentation in REM and NREMSleep: ‘Covert’ REM Sleep as a Possible Reconciliation ofTwo Opposing Models”,Behavioral and Brain Sciences,23(6): 851–866.
• –––, 2010, “Dream Analysis andClassification: The Reality Simulation Perspective”,inPrinciples and Practice of Sleep Medicine, M. Kryger,T. Roth, and W.C. Dement (eds.), New York: Elsevier,pp. 595–603.
• Nielsen, T.A. and J. Lara-Carrasco, 2007, “Nightmares,Dreaming, and Emotion Regulation: A Review”, in Barrett andMcNamara 2007b: 253–284.
• Nielsen, T.A. and R. Levin, 2009, “Theories and Correlatesof Nightmares”, in Stickgold and Walker 2009:323–329.
• Nielsen, T.A. and P. Stenstrom, 2005, “What Are the MemorySources of Dreaming?”,Nature, 437(7063):1286–1289.
• Nielsen, T.A., D. Deslaurier, and G. Baylor, 1999, “Emotionsin Dream and Waking Event Reports”,Dreaming, 1:287–300.
• Nielsen, T.A., L. Ouellet, and A.L. Zadra, 1995, “PressureStimulation during REM Sleep Alters Dream Limb Activity and BodyBizarreness”,Sleep Research, 24: 134.
• Nielsen, T.A., C. Svob, and D. Kuiken, 2009,“Dream-Enacting Behaviors in a NormalPopulation”,Sleep, 32(12): 1629–1636.
• Nir, Y. and G. Tononi, 2010, “Dreaming and the Brain: FromPhenomenology to Neurophysiology”,Trends in CognitiveSciences, 14(2): 88–100.
• Noë, A., 2004,Action in Perception, Cambridge, MA& London: MIT Press.
• Olson, E.T., 2010, “Personal Identity”,TheStanford Encyclopedia of Philosophy (Winter 2010 Edition),E.N. Zalta (ed.), URL =<https://plato.stanford.edu/archives/win2010/entries/identity-personal/>.
• O'Shaughnessy, B., 2002,“Dreaming”,Inquiry, 45: 399–432.
• Pace-Schott, E.F., 2007, “The Frontal Lobes andDreaming”, in Barrett and McNamara 2007b: 115–154.
• –––, 2013, “Dreaming as a Story-TellingInstinct”,Frontiers in Psychology, 4,doi:10.3389/fpsyg.2013.00159[available online]
• Pagel, J.F., M. Blagrove, R. Levin, B. States, B. Stickgold, andS. White, 2001, “Definitions of Dream: A Paradigm for ComparingField Descriptive Specific Studies of Dream”,Dreaming,11: 195–202.
• Perogamvros, L., T.T. Dang-Vu, M. Desseilles, S. Schwartz, 2013,“Sleep and Dreaming Are for ImportantMatters”,Frontiers in Psychology, 4,doi:10.3389/fpsyg.2013.00474[available online]
• Plato,Phaedrus, B. Jowett (ed.), inThe InternetClassics Archive,available online.
• –––,Theaetetus, B. Jowett (ed.),inThe Internet Classics Archive,available online.
• Putnam, H., 1981, “Brains in a Vat”, inReason,Truth and History, H. Putnam (ed.), Cambridge & New York:Cambridge University Press, pp. 1–21.
• –––, 1962 [1986], “Dreaming and‘Depth Grammar’”, inAnalytical Philosophy FirstSeries, R. Butler (ed.), Oxford: Basil Blackwell & Mott; pagereference is to the reprint in H. Putnam (ed.),1986,Philosophical Papers, Vol. 2.: Mind, Language andReality, Cambridge: University Press, pp. 304–324.
• Rechtschaffen, A. and C. Buchignani, 1992, “The VisualAppearance of Dreams”, inThe Neuropsychology of Sleep andDreaming, J.S. Antrobus and M. Bertini (eds.), Hillsdale, N.J.:Lawrence Erlbaum, pp. 143–156.
• Reed, T.M., 1979, “Dreams, Scepticism and WakingLife”, inBody, Mind, and Method. Essays in Honor of VirgilC. Aldrich, D.F. Gustafson and B.L. Tapscott (eds.), Dodrecht& Boston: D. Reidel Publishing Company, pp. 37–64.
• Resnick, J., R. Stickgold, C.D. Rittenhouse, and J.A. Hobson,1994, “Self-Representation and Bizarreness in Children’sDream Reports Collected in the Home Setting”,Consciousnessand Cognition, 3: 30–45.
• Revonsuo, A., 2000, “The Reinterpretation of Dreams: AnEvolutionary Hypothesis of the Function ofDreaming”,Behavioral and Brain Sciences, 23:877–901.
• –––, 2005, “The Self in Dreams”,inThe Lost Self. Pathologies of the Brain and Identity,T.E. Feinberg and J.P. Keenan (eds.), Oxford: Oxford University Press,pp. 206–219.
• –––, 2006,Inner Presence: Consciousness asa Biological Phenomenon, Cambridge, MA & London: MITPress.
• Revonsuo, A. and C. Salmivalli, 1995, “A Content Analysisof Bizarre Elements in Dreams”,Dreaming,5:169–187.
• Revonsuo, A. and K. Tarkko, 2002, “Binding in Dreams. TheBizarreness of Dream Images and the Unity ofConsciousness”,Journal of Consciousness Studies, 9:3–24.
• Rosen, M.G., 2013, “What I Make up when I Wake up:Anti-Experience Views and Narrative Fabrication ofDreams”,Frontiers in Psychology, 4,doi:10.3389/fpsyg.2013.00514[available online]
• Rosen, M.G. and J. Sutton, 2013, “Self-Representation andPerspectives in Dreams”,Philosophy Compass, 8(11):1041–1053.
• Ruby, P., C. Blochet, J.-B. Eichenlaub, O. Bertrand, D. Morlet,and A. Bidet-Caulet, 2013, “Alpha Reactivity to First NamesDiffers in Subjects with High and Low Dream RecallFrequency”,Frontiers in Psychology, 4,doi:10.3389/fpsyg.2013.00419[available online]
• Russell, B., 1914,Our Knowledge of the External World as aField for Scientific Method in Philosophy, London & New York:Routledge (2009).
• –––, 1948,Human Knowledge: It's Scope andLimits, London & New York: Routledge (2009).
• Ryle, G., 1949,The Concept of Mind, Chicago: Universityof Chicago Press (2000).
• Sartre, J.-P., 1940,L'imaginaire: Psychologiephénoménologique de l'imagination, Paris: Gallimard(2005).
• Sauvageau, A., T.A. Nielsen, and J. Montplaisir, 1998,“Effects of Somatosensory Stimulation on Dream Content inGymnasts and Control Participants: Evidence of VestibulomotorAdaptation in REM Sleep”,Dreaming, 8:125–134.
• Scarone, S., M.L. Manzone, O. Gambini, I. Kantzas, I. Limosani,A. D’Agostino, and J.A. Hobson, 2007, “The Dream as aModel for Psychosis: An Experimental Approach Using Bizarreness as aCognitive Marker”,Schizophrenia Bulletin, 34(3):515–522.
• Schenck, C.H. 2005,Paradox Lost: Midnight in theBattleground of Sleep and Dreams, Minneapolis: Extreme Nights,LLC.
• Schenck, C.H. and M.W. Mahowald, 1996, “REM SleepParasomnias”,Neurological Clinics, 14:697–720.
• Scherner, K.A., 1861,Das Leben des Traumes, Berlin:Verlag von Heinrich Schindler.
• Schooler, J.W., J. Smallwood, K. Christoff, T.C. Handy,E.D. Reichle, and M.A. Sayette, 2011, “Meta-awareness,Perceptual Decoupling and the Wandering Mind”,Trends inCognitive Sciences, 15(7): 319–326.
• Schopenhauer, A., 1847,Kleinere Schriften, Zürich:Haffmans Verlag (1988).
• Schredl, M., 2006, “Factors Affecting the Continuitybetween Waking and Dreaming: Emotional Intensity and Emotional Tone ofthe Waking-Life Event”,Sleep and Hypnosis, 8:1–5.
• –––, 2010, “History of Dream Research: TheDissertation ‘Entstehung der Träume (Origin ofDreams)’ of Wilhelm Weygandt Published in1893”,International Journal of Dream Research, 3(1):95–97.
• Schredl, M. and F. Hofmann, 2003, “Continuity between WakingActivities and Dream Activities”,Consciousness andCognition, 12: 298–308.
• Schredl, M., A. Fuchedzhieva, H. Hämig, and V. Schindele,2008, “Do We Think Dreams Are in Black and White Due to MemoryProblems?”,Dreaming, 18(3): 175–180.
• Schröder, S., 1997, “The Concept of Dreaming: On ThreeTheses by Malcolm”,Philosophical Investigations,20(1): 15–38.
• Schwitzgebel, E., 2002, “Why Did We Think We Dreamed inBlack and White?”,Studies in History and Philosophy ofScience, 33: 649–660.
• –––, 2003, “Do People Still ReportDreaming in Black and White? An Attempt to Replicate a Questionnairefrom 1942”,Perceptual and Motor Skills, 96:25–29.
• –––, 2011,Perplexities ofConsciousness, Cambridge & London: MIT Press.
• –––, 2014, “Belief”,TheStanford Encyclopedia of Philosophy (Spring 2014 Edition),E.N. Zalta (ed.), forthcoming URL =<https://plato.stanford.edu/archives/spr2014/entries/belief/>.
• Schwitzgebel, E., C. Huang, and Y. Zhou, 2006, “Do We Dreamin Color? Cultural Variations andSkepticism”,Dreaming, 16(1): 36–42.
• Sebastián, M., 2014, “Dreams: An Empirical Way toSettle the Discussion between Cognitive and Non-Cognitive Theories ofConsciousness”,Synthese, 191(2): 263–285.
• Sextus Empiricus,Outlines of Pyrrhonism, R.G. Bury(ed.), Cambridge, MA: Harvard University Press (1987).
• Shoemaker, D., 2014, “Personal Identity andEthics”,The Stanford Encyclopedia of Philosophy(Spring 2014 Edition), E.N. Zalta (ed.), forthcoming URL =<https://plato.stanford.edu/archives/spr2014/entries/identity-ethics/>.
• Siegler, F.A., 1967, “Remembering Dreams”,ThePhilosophical Quarterly, 17: 14–24.
• Silberer, H., 1919,Der Traum: Einführung in dieTraumpsychologie, Stuttgart: Ferdinand Enke.
• Singer, E.A., 1924, “On Pain in Dreams”,TheJournal of Philosophy, 21(22): 589–601.
• Smith, A.D., 2002,The Problem of Perception, Cambridge,Mass.: Harvard University Press.
• Solms, M., 1997,The Neuropsychology of Dreams: AClinico-Anatomical Study, Mahwah, NJ: Lawrence Erlbaum.
• –––, 2000, “Dreaming and REM Sleep AreControlled by Different Brain Mechanisms”,Behavioral andBrain Sciences, 23: 843–850.
• Sosa, E., 2007,A Virtue Epistemology: Apt Belief andReflective Knowledge, Volume I, Oxford: Clarendon Press.
• Stickgold, R. and M.P. Walker (eds.), 2009,The Neuroscienceof Sleep, London, Burlington MA, San Diego: Elsevier: AcademicPress.
• Stone, J., 1984, “Dreaming andCertainty”,Philosophical Studies, 45(May):353–368.
• Stroud, B., 1984,The Significance of PhilosophicalScepticism, Oxford: Clarendon Press.
• Stumbrys, T., D. Erlacher, M. Johnson, and M. Schredl, M., 2014,“The Phenomenology of Lucid Dreaming: An OnlineSurvey”,American Journal of Psychology, 127(2):191–204.
• Symons, D., 1993, “The Stuff that Dreams Aren't Made of:Why Wake-State and Dream-State Sensory ExperiencesDiffer”,Cognition, 47(3): 181–217.
• Uslar, D. von, 1964,Der Traum als Welt: Untersuchungen zurOntologie und Phänomenologie des Traums, Pfullingen:Neske.
• Uzgalis, W. 2014, “John Locke”,The StanfordEncyclopedia of Philosophy (Spring 2014 Edition), E.N. Zalta(ed.), URL =<https://plato.stanford.edu/archives/spr2014/entries/locke/>.
• Valberg, J.J., 2007,Dream, Death, and the Self,Princeton & Oxford: Princeton University Press.
• Valli, K., 2008,Threat Simulation: The Function ofDreaming?, doctoral thesis, Turku: Annales UniversitatisTurkuensis.
• van de Castle, R.L., 1994,Our Dreaming Mind, New York:Ballantine Books.
• van Eeden, F., 1913, “A Study ofDreams”,Proceedings of the Society for PsychicalResearch, 26: 431–461.
• Vold, J.M., 1910/1912,Über den Traum, Vol. I andII, edited by O. Klemm, Leipzig: Johann Ambrosius Barth.
• Voss, U., R. Holzmann, I. Tuin, and J.A. Hobson, 2009,“Lucid Dreaming: A State of Consciousness with Features of BothWaking and Non-Lucid Dreaming”,Sleep, 32(9):1191–1200.
• Walker, M.P., 2009, “Sleep-Dependent MemoryProcessing”, in Stickgold and Walker 2009: 230–240.
• Wamsley, E.J., 2013, “Dreaming, Waking ConsciousExperience, and the Resting Brain: Report of Subjective Experience asa Tool in the Cognitive Neurosciences”,Frontiers inPsychology, 4, doi:10.3389/fpsyg.2013.00637[available online]
• Wamsley, E.J. and R. Stickgold, 2009, “Incorporation ofWaking Events into Dreams”, in Stickgold and Walker 2009:330–336.
• –––, 2010, “Dreaming and Offline MemoryProcessing”,Current Biology, 20(23):R1010–1013.
• Wamsley, E.J., M. Tucker, J.D. Payne, J.A. Benavides, andR. Stickgold, 2010, “Dreaming of a Learning Task Is Associatedwith Enhanced Sleep-Dependent Memory Consolidation”,CurrentBiology, 20(9): 850–855.
• Waxman, W., 1994,Hume's Theory of Consciousness,Cambridge & New York: Cambridge University Press.
• Weygandt, W., 1893,Entstehung der Träume, Leipzig:Grübel & Sommerlatte.
• Williams, B., 1978,Descartes: The Project of PureEnquiry, Middlesex: Pelican Books.
• Windt, J.M., 2010, “The Immersive SpatiotemporalHallucination Model of Dreaming”,Phenomenology and theCognitive Sciences, 9: 295–316.
• –––, 2011, “Altered Consciousness inPhilosophy”, inAltering Consciousness. MultidisciplinaryPerspectives, Volume 1: History, Culture, and the Humanities,E. Cardeña and M. Winkelman (eds.), Santa Barbera, Denver &Oxford: Praeger, pp. 229–254.
• –––, 2013, “Reporting Dream Experience:Why (Not) to Be Skeptical about Dream Reports”,Frontiers inHuman Neuroscience, 7, doi:10.3389/fnhum.2013.00708[available online]
• Windt, J.M. and T. Metzinger, 2007, “The Philosophy ofDreaming and Self-Consciousness: What Happens to the ExperientialSubject during the Dream State?”, in Barrett and McNamara 2007c:193–248.
• Windt, J.M. and V. Noreika, 2011, “How to Integrate Dreaminginto a General Theory of Consciousness—A Critical Review ofExisting Positions and Suggestions for FutureResearch”,Consciousness and Cognition, 20(4):1091–1107.
• Wittgenstein, L., 1953,Philosophical Investigations,G.E.M. Anscombe (ed.), Oxford: Blackwell.
• –––, 1967,Zettel, G.E.M. Anscombe andG.H. von Wright (eds.), Berkeley: University of California Press.
• Wundt, W.M., 1896,Grundriss der Psychologie, Leipzig:Engelman; page reference is to the excerpt translated by C.H. Judd,reprinted in R.L. Woods and H.B. Greenhouse (eds.),The New Worldof Dreams, New York: Macmilllan (1974), pp. 179–180.

Academic Tools

	How to cite this entry.
	Preview the PDF version of this entry at theFriends of the SEP Society.
	Look up this entry topicat theIndiana Philosophy Ontology Project(InPhO).
	Enhanced bibliography for this entryatPhilPapers, with links to its database.

Other Internet Resources

• Philosophy of Dreaming,entry in theInternet Encyclopedia of Philosophy.
• Dreams,PhilPapers collection.
• Dreams and Skepticism,PhilPapers collection.

Related Entries

belief |Berkeley, George |delusion |Descartes, René: epistemology |imagination |Locke, John |perception: the problem of |personal identity |personal identity: and ethics |Plato: on knowledge in theTheaetetus |sense-data |skepticism |skepticism: and content externalism

Acknowledgments

I want to thank Regina Fabry and two anonymous reviewers forhelpful comments and constructive criticism on an earlier version ofthis manuscript. And as always, I am greatly indebted to Stefan Pitz for his support.