In recent decades, philosophers frequently refer to‘intentionality’, roughly, that feature of beliefs,desires, and other mental states in virtue of which they areof orabout something or more generally, possesscontent; contrary to what ordinary usage of ‘intentional’might suggest, it is not limited to practical states such as intendingto do something or acting intentionally. The currency of the technicalterm is due in large part to Edmund Husserl, who took it from his ownteacher, Franz Brentano. In 1874, Brentano had proposed this featureas a criterion of the mental that could be used to demarcatepsychology from the physical sciences, and he explicitly invokedmedieval scholastic terminology (intentio,esseintentionale) as a way of reintroducing the notion.Brentano’s thesis about the criterion of the mental has had acheckered fate in philosophy. But interest in intentionality in itsown right has continued unabated.

This interest has naturally led to questions about the history of thenotion. Earlier accounts, following Brentano, looked to late medievaldiscussions in Latin and then to their roots in earlier Arabicphilosophy. But at that point, it was claimed, the trail peters out– nothing in Greek or Roman philosophy, allegedly, corresponds.This narrative, as one might suspect, rests on questionableassumptions. Once the investigation is properly framed, it is clearthat philosophical interest in intentionality can be traced all theway back to the origins of Western philosophy. Intentionality isrecognized as raising serious puzzles already in the early- tomid-fifth centurybce, arguably first byParmenides, but then indisputably by sophists responding to him,including Gorgias and Protagoras. The first extensive discussions arein Plato, who explicitly thematizes the difficulties in severaldialogues and considers various solutions. Later philosophers developother solutions, which include appeals to internal representations(Aristotle), or to nonexistent objects of thought (the first Stoics,Zeno and Cleanthes), and propositions and other semantic entities(other Stoics, beginning with Chrysippus). Even the terminology ofintentionality can be traced back, through Augustine, to Greekorigins, namely in the Stoic theory of vision.

• 1. The history of the term
• 2. The history of the problem
• 3. Before Plato
• 4. Plato
• 5. Aristotle
• 6. The Stoics
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. The history of the term

The received view, which takes the notion to originate in Arabicphilosophy, traces back to an article by the phenomenologist HerbertSpiegelberg, originally published in 1933 (for a translation of arevised version, see Spiegelberg 1976). It turns entirely onphilosophical terminology: it only considers texts that use cognatesof ‘intention’ in a specific technical sense, that of amental act’sbeing directed at orreferring tosomething, in contrast with a usage that applies exclusively topractical contexts, where an agent intends to do something.Spiegelberg claims that before the high scholastic period, uses of theLatinintentio were exclusively practical and so have nobearing on the problem of the intentionality of mental states moregenerally. The closest antecedents, he claims, are the Arabicma’na andma’qul, which were translatedinto Latin in the high scholastic period byintentio.

Even when considered simply as a history of the terminology, thisaccount is seriously mistaken. Late scholastic discussions often citeAugustine, in particular Book XI of hisOn the Trinity, inwhichintentio plays a central role. And while Augustine doesidentifyintentio there with will (uoluntas) andeven love (amor), he does not have practical concernsexclusively or even primarily in mind. On the contrary, his focus ison cognition, starting with vision and continuing on with memory,thought, and self-knowledge. It is just that he thinks that in orderto account for the directedness of these states, their analysis mustultimately include a certain practical element, rather than the otherway around, where all practical attitudes must be explained in termsof cognition. Augustine argues that vision and perception generallycannot be analyzed simply into subject and object (as onAristotle’s account). That would leave out something essential,which is needed to direct the sense to the perceptible object and keepit fixed on it. Augustine identifies this third element as theperceiver’sintentio, which he characterizes as a kind ofstriving or will. It is precisely because a trio of factors arerequired, in fact, that he believes psychology can be useful toTrinitarian theology. Since humans are made in God’s image, eachhuman (or more precisely, each “inner man”) must alsoreplicate God’s triune structure. The roleintentioplays in cognition is parallel to that of the Holy Spirit, mediatingbetween the Father and the Son: it mediates between the object and thecognitive faculty. Later scholastics were thus right to citeAugustine’s use ofintentio in discussions ofcognition, establishing a direct link to late antiquity, independentof the contributions of Arabic philosophy, in the history of whatSpiegelberg called “extra-practical” intentionality.

Augustine, moreover, is adapting and developing earlier Greek views.In Book XII of hisLiteral Commentary on Genesis, he offersan extensive analysis of vision that relies heavily on Stoic theory.In both theories, vision depends on the active role of theperceiver’spneuma (Greek) orspiritus (Latin),“breath” in its original meaning and for the Stoics a kindof hot gaseous body, but for Augustine something immaterial. (The samewords, not insignificantly, are used in the Christian scriptures forthe Holy Spirit). Vision occurs when thepneuma extendsthrough the optic nerve and the eye to the object, either by reachingout through the pupil to make contact with the object directly (as onAugustine’s theory) or by pricking and tensing the intervening airbeginning at the pupil into a cone with its base at the object (as onthe Stoic theory). The words that the Stoic Chrysippus uses for theextension of the visual cone to the object are the Greek verbenteinein and nounentasis (Diogenes Laertius VII157), which are cognate with the Latinintendere andintentio. So if our goal was to find not just a continuoustransmission of technical terminology for intentionality, but cognatesofintentio, we could trace it back at least to Greektheories of vision in the third centurybce,if not still earlier extromission theories of vision. (For furtherdiscussion of Augustine’s theory, as well as the history of theterminology, see Caston 2001.)

Other expressions and figures of speech familiar to us from moderndiscussions of intentionality can be found in ancient philosophy, eventhough we cannot trace a continuous connection from them to our ownusage. Throughout antiquity, for example, we find the antithesis of‘presence in absence’ (parōn apōn) todescribe the way a mental state can make something“present” to the subject that is nevertheless absent fromthe current surroundings and perhaps even from reality altogether.Aristotle mentions such presence in absence explicitly as anaporia or difficulty that must be resolved (On Memory andRecollection 1, 450a25 ff.). Certain Stoics speak of immanentobjects of thought, items that are literally present “inthought” (ennoēmata). Later thinkers use thephrase ‘existing in mere thoughts alone’ (en psilaisepinoiais monais) to characterize merely intentional objects,which do not exist in reality. Even the metaphor of directedness– of aiming the mind at something (intendere animumin), like an arrow – can be found in ancient texts. InPlato’sCratylus (420b–c),Socratessuggests that the word for belief,doxa, derivesetymologically from the word for bow,toxon: it “goestoward” each thing and how it is in reality. Socrates thenextends this analysis to the vocabulary for deliberative states: theword for plan,boulē, for example, derives from the wordfor shot,bolē. The metaphor is repeated again in theTheaetetus (194a): someone whobelieves falsely is “like a bad archer who, in shooting, goeswide of the mark and errs”.

2. The history of the problem

A history of terminology, though, even when done correctly, tracks thewrong items. The same technical terms are often used to express verydifferent concepts: just consider the philosophical usage of termslike ‘substance’, ‘matter’, or even‘concept’ itself. Conversely, the same concept is oftenexpressed by different terms, some of which may not be technical atall, a situation that is especially likely at the beginning of inquiryinto a subject. So if terminology is to be used as evidence, much moremust be brought into consideration – simple word searches willnot do.

The terminology, moreover, holds little interest in its own right. Inorder for a history to be philosophically illuminating, it shouldfocus on the concept of intentionality itself or, better still, thedivergent conceptions of intentionality that philosophers have had andtheir resulting disagreements. These differences afford us thegreatest perspective on our own presuppositions and preoccupations, aswell as revealing paths and solutions we might not otherwise haveconsidered. There is thus no need to settle on a single conception asthe concept of intentionality at the outset, which would inany case only produce a Whiggish history, of development towards anddeviations from some favored, but undoubtedly idiosyncratic view. Onthe contrary, we should take the opposite approach: substantivedisagreements between philosophers are potentially the mostinstructive philosophically.

A philosophical history would therefore do better to focus on thehistory of theproblem of intentionality: the difficulty,that is, of providing a philosophically adequate account of the natureof intentionality in light of its various peculiarities, whateverterms may have been used to express it. Such an approach not onlyallows room for different theories of intentionality, but alsodivergent conceptions, as well as attempts to dissolve the problem,either by dismissing the phenomenon entirely or by denying that thereis any genuine difficulty involved. A history of intentionality thatdid not include a Parmenides or a Quine would not be very informative,especially if we are trying to understand the difficulty and what isat stake.

The problem of intentionality is the problem of explaining what it isin general for mental states to have content, as well as theparticular conditions responsible for specific variations in content.The difficulty of providing such an account lies in explaining whymental states often seem to violate familiar entailment patterns(whether or not we take such violations to be criterial ofintentionality). To begin with, the content of many mental states doesnot correspond with what is in the world: what we imagine may notexist, our beliefs may be false, our desires may go unfulfilled. Toput it more paradoxically, a mental state may be about something, evenif there isn’t any such thing in the world. This is one of anumber of peculiarities that prove difficult to account for, and whichare sometimes thought to pose a particular stumbling block fornaturalistic approaches to the mind. As Wittgenstein once quipped, youcan’t hang a man unless he is there, but you can look for himeven if he’s not, or even if he does not exist at all(Philosophical Investigations 1.133, §462). There areother peculiarities as well, concerning our ability to focusselectively on certain aspects of objects, without having others inmind. For example, while I cannot greet a person without greeting aperson of some particular height, I can think of a person withoutthinking of a person of any particular height. I can also entertaindifferent attitudes to the same object at the same time, depending onthe aspect under which I consider it. So I might believe that theMorning Star is a star but that Venus is not one, despite the factthat Venusis the Morning Star; yet for just the same reason,we cannot land a space probe on the one without thereby landing it onthe other. These and other difficulties form a loose family ofphenomena that give rise to the problem of intentionality. Differentphilosophers may regard these phenomena differently, perhaps focusingon some but not others, or even excluding some as not belongingtogether with the rest. A philosophical history should be generousabout such differences: what is important philosophically is that aphilosopher recognizes that some of them pose a difficulty, at leastprima facie, in accounting for mental states. (For furtherdiscussion of the methodology, see Caston 2001)

3. Before Plato

Parmenides of Elea (early 5th centurybce) isarguably the first Greek philosopher to have focused on theproblematic nature of intentionality. His poem (transmitted under thetitleOn Nature) offers a startling revelation of theallegedly true nature of reality and appearance, in which the narratoris instructed by a goddess that “you cannot grasp or expresswhat is not – it cannot be accomplished” (B2), for“thinking cannot be found apart from what is, upon which itsexpression depends” (B8.35–36) and “what can be saidand thought must be what is” (B6). The Greek for the phrases‘what is’ and ‘what is not’ are notoriouslyambiguous. But if, as many interpreters maintain (see Owen 1960; Furth1968), it should be construed here either in terms of (a)what does or does notexist, or (b) whatisoris not the case, or perhaps (c) some fusion ofthe two, then the goddess is denying the possibility of thinking orspeaking either about nonexistent objects, or about nonfactualstates-of-affairs, or both, on the basis of the following intuitions.If one is to think or express anything at all, there mustbesomething that one is thinking or expressing (thus quantifying in).But what is not, by hypothesis,is not there to be thought of(cf. B3), since either it does not exist or is not in fact the case;and if there isn’t anything there to be thought of, then we mustnot be thinking of anything either. Parallel problems are supposed toarise in the case of speech, for statements concerning a nonexistentor for false statements.

Concerns about non-existent objects or non-factual states of affairsare not explicit in Parmenides’ poem, though –unsurprisingly, the goddess does not give examples of what she isproscribing. This leaves room for other construals of ‘what isnot’, such as the view that it always requires completion orspecification as ‘what is notF’ for some valueofF, so that ‘what is not’ raises concerns aboutnegative predication instead, especially in explanatory andcosmological contexts. But of course the precise nature of thedifficulty here is not spelled out either, so speculativereconstruction is required. In any case, the goddess herself seems touse negation and the phrase ‘what is not’ quite freely,though perhaps this is just symptomatic of her liminal position at theborders of Night and Day (B1).

Whatever Parmenides intended, it is clear that the subsequentreception of his poem is concerned precisely with the problem sketchedabove about what does not exist and what is not the case. Numerousproscriptions similar to the goddess’s are reported in theremainder of the 5th century, though offered by philosophers withquite different motivations and agendas, including Protagoras,Gorgias, the author of pseudo-Hippocratic treatiseOn theArt, Anaxagoras, Metrodorus of Chios, Euthydemus, Cratylus, andAntisthenes. In many of these cases, the denial is explicitlyformulated as a rejection of the possibility of falsehood, of thinkingor speaking of what is not the case.

The sophists Protagoras and Gorgias are of particular interest.According to Plato, Protagoras held that one cannot believe what isnot and that whatever one experiences is true (Theaetetus167a). This fits snugly with Protagoras’widely attested doctrine that each human being is “the measureof all things,” which, on any interpretation, excludes thepossibility of error. But Protagoras’ endorsement reveals aninteresting subtlety in the Parmenidean thesis that what is not cannotbe thought about – or more positively, the thesis that ifsomething is had in mind, it must be. The goddess in Parmenides’poem uses this thesis in a negative fashion, moving from theassumption that certain things ‘are not’ to theparadoxical conclusion that we cannot actually think about themeither. But one might equally use it in a positive fashion, asProtagoras seems to have done, to move from the assumption that wecan in fact think of such things to the conclusion that theymust in fact ‘be’, i.e. exist or obtain, after all. Initself, the Parmenidean thesis only makes a conditional claim, andprima facie it seems open to employ eithermodustollens ormodus ponens. Depending on whether oneretains commonplace assumptions about what we can think or about whatthere is in the world, the Parmenidean thesis can lead to either abloated ontology or a very restricted psychology.

Gorgias challenges this thesis in his treatiseOn Not Being(preserved in two slightly different versions in thepseudo-AristotelianOn Melissus, Xenophanes, and Gorgias andin Sextus Empiricus’Adversus Mathematicos VII 65 ff.).It takes direct aim at Eleatic assumptions, and especially those ofParmenides, by arguing that (i) there isn’t anything; (ii) evenif there is something, it cannot be known; and finally, (iii) even ifsomething can be known, one could not inform anyone of this. Thesecond part is of particular interest, since Gorgias offers areductio ad absurdum of the Parmenidean thesis, especiallywhen deployed in the positive way we have just seen in Protagoras.Given that we obviously can have in mind, for example, a chariot-teamracing on the sea – in fact, just by reading this, you have putit in mind – it should follow from the Parmenidean thesis thatthereis a chariot-team racing on the sea; but (paceProtagoras) plainly there is not. If both these intuitions aremaintained, the only option left is to reject the Parmenidean thesisitself: it isnot the case that one can only think or speakof what is – thought is not so tightly bound to reality. Gorgiasimmediately goes on to argue for a sceptical conclusion, on thegrounds that we have no basis for telling which mental statescorrespond to reality and which do not, and so cannot know anything atall. But this further argument rests on having shown that our ordinaryintuitions about what we can think and what exists or obtains togetherundermine the Parmenidean thesis. (For further discussion, see Caston2002a)

Why should anyone be tempted by the Parmenidean thesis in the firstplace? A simple intuition may lie behind it, namely, that thoughtconsists in adirect relation to what is thought about (andmutatis mutandis for other mental states and what they areabout). For given that a relation cannot obtain unless all its relataexist or obtain, it will follow that we cannot ever think of what doesnot exist or obtain (“what is not”). To the extent thatthis direct relational model has a grip on us, we will be forced toeither Parmenidean or Protagorean conclusions. In fact, we canreformulate these assumptions together as an inconsistent triad (using‘thought’ schematically for mental states more generally,and allowing for the ambiguity between ‘exists’ and‘obtains’):

1. Thought consists in a direct relation to what is thoughtabout.
2. No relation can obtain unless all its relata exist/obtain.
3. Sometimes we can think about what does not exist/obtain.

Each of these theses possesses a certain intuitive appeal. But takentogether, they are inconsistent, and so at least one has to be givenup. This does not entirely force our hand, however, since any two ofthe three are mutually consistent. So there is still room fordisagreement among the disputants. As we have seen, some 5th centurythinkers, including Parmenides himself (on some interpretations) choseto maintain (A) and (B), and reject (C). But if this seems too costly,as it does to most people, one would need to reject one of the othertwo theses instead. An obvious candidate for rejection is (A), thatthought consists in a direct relation to what is thought about. Butthere are different ways of going about it. Someone could simply (i)reject a relational analysis altogether. But one could also reject (A)while continuing to accept a relational analysis, so long as (ii) itinvolves a relation tosomething else other than what isthought about. Much of the subsequent discussion in ancient philosophycan be seen as an attempt to pursue the latter strategy, (ii), byfinding a suitable intermediary: for example, certain Platonistsappeal to Forms; Aristotle appeals to changes within our body thatserve as internal representations; the Stoics from Chrysippus onwardsappeal to abstract semantic objects like propositions; and Epicurusappeals to parts of the surfaces of bodies. A third main option,though, would be to retain the direct relational model in (A)unchanged, while also preserving the phenomenological intuition in(C), and instead abandon the metaphysical assumption in (B), as theearliest Stoics did. Whenever one thinks, these Stoics insist, thereis something that one is thinking about; but it needn’tbe anything thatexists orobtains. On this Stoicview, there are things that do not exist or obtain, which can serve asintentional objects of thought and other mental states.

4. Plato

Throughout his dialogues, Plato emphasizes the relational character ofvarious mental states: sight, hearing, touch and perception generally,memory, belief, knowledge, concepts, speech, love (Tht.152c, 160a–b,163e, 188d–189b;Rep.V, 476e, 478b;Parm. 132b–c;Soph. 262e,263c;Symp. 199d).In each case, Socrates (or the other mainspeaker) asks whether the mental state in question is “ofsomething or of nothing”, and the interlocutors agree that it isalwaysof something – it is impossible for such a statenot to be of anything at all. In theCharmides, Socrates getsCritias to agree to something stronger, namely, that many of thesestates – seeing, hearing, and other forms of perception, desire,intention, love, fear, and belief – must have an objectother than themselves; and he suggests that it would be oddif knowledge were not like this as well (167c–168a).But in thisregard, mental states do not differ from other relatives, as hehimself emphasizes: Socrates sometimes adds nonintentional cases, suchas siblings, parents and children, and doubles and halves, in order toillustrate his point. In some of the passages above, Socrates followsup this question with a further one, which has bearing only for themental states, namely, whether they are always of something“that is” rather than something “that is not”.Although the speakers readily agree that these states must always beof something that is, the problem of intentionality already looms,merely by his raising the possibility that on occasion some statesmight be of what is not, either of what is not the case or of whatdoes not exist. In thePhilebus, this alternative isexplicitly taken up: just as one can believe something without thatbelief being of anything that ever was, is, or will be, so one canfeel pleasure about something, or fear, anger, and so on, even if itis not about anything that ever was, is, or will be. In all suchcases, the beliefs, pleasures, fears, and so on are said to be“false” (pseudē,Phlb.40c–e).

More importantly, there are several passages where Socrates discussesfalsehood in belief and speech at length, as a familiar and importantproblem in need of resolution. In theCratylus, Socrates saysthat a great many people, both in the past and in the present, haveheld that it is impossible to speak falsely, on the grounds that it isimpossible to say something without saying somethingthat is;Cratylus concludes that in such cases, instead of speaking falsely andsaying something that is not, the speaker would simply be makingnoise, no more meaningful than banging a pot (429d–430a).A similarpuzzle about false speech is posed in theEuthydemus,initially by the brothers Euthydemus and Dionysodorus, a visiting tagteam of Sophists who are displaying their eristic prowess (283e–284e).It is laterreprised by Socrates, who attributes it explicitly to“Protagoras’ followers” and still earlier thinkers,and it is explicitly extended to false belief as well (286c–d).These versionsof the puzzle frame it in terms of whether one can speak (or think) of“what is not”: one cannot speak without there beingsomething that one is saying (or thinking); yet it is impossible forthere to be such a thing and for it not to be. But that is whatspeaking falsely would amount to, since on this view speaking falselyjust is to say something that is not. Plato never explicitly questionsthe relational character of speaking and believing or rejects therequirement that the relata must exist or obtain. In the inconsistenttriad we considered above, it is the third proposition,“Sometimes we can think about what does not exist/obtain,”which is consistently under pressure in these contexts. At the sametime, Socrates objects that such a position would be self-undermining(Euthyd. 287e–288a),though he does not offer a further diagnosishere.

The puzzle about false belief recurs in theTheaetetus at acrucial juncture in the dialogue’s main argument. Socrates andTheaetetus have rejected the proposal that knowledge is perception andwith it the underlying Protagorean view that whatever appears to bethe case is the case. Theaetetus’ new proposal, that knowledgeis true belief, offers no advance, though, unless they can show thatfalse belief is possible, against sophistic puzzles like we have justseen from theEuthydemus; and while Socrates says he has“often” worried about this, he claims that he is unable tosay what false belief is and how it comes about (187b–e).He then developsthe worry in much more elaborate ways than before. There is a fullerversion of the puzzle than we have seen so far, which explicitlyequates believing something “that is not” with notbelieving anything at all (188d–189b).But Socrates also introduces a distinct, newpsychological worry into consideration. If one assumes that falsebelief by its very nature has a certain structure, namely, ofmistaking one thing for another, we must then ask what our cognitiveaccess is to each: do we know each of these, or only one, or neither?(188a–c)Socrates makes this underlying structure explicit when he goes on toanalyze false belief as a kind of “other-believing”(allodoxia), where we say in thought that something is onething instead of another (189c–190e).This analysis avoids the earlier difficulty,since both items can be things that are, and it locates error in ourhaving latched on to the wrong one. From a third-person point of view,this is illuminating, since it exposes precisely why the belief ismistaken. But for just the same reason the description is unacceptablefrom a first-person point of view for the subject who is taken in: noone, Socrates insists, would ever sayto themselves thatSocrates is Theaetetus or that one thing is something distinct from it(190a–c). And infact Plato repeatedly characterizes thinking as saying something tooneself, both in this dialogue (189e–190a)and later intheSophist (263e–264a);an analogous view also seems to be implicit inthe image fromPhilebus 38e–39aof an internalscribe writing out our beliefs in our soul. This treatment ofother-believing in theTheaetetus thus seems to presupposethat both terms must be somehow present to thought in order for thesubstitution to occur (190d). The possibilitythat one might have only one of them in the mind, through perceptionor in some other way, and somehow apply it to the wrong thing in theworld is not considered (even though it is something that Plato allowsin the case of incorrect names atCratylus 430a–431b,where hespeaks of pointing or otherwise exhibiting the thing while applying aname to it).

At this point in theTheaetetus, Socrates proposes a modelfor how false belief can occur, based on an analogy with how signetrings can be impressed into a wax block to produce a sealing: in asimilar way, our thoughts and perceptions make an impression on ourmemory, leaving behind traces which are signs or representations ofthe original objects thought about or perceived (191c–d;194c–d).These traces canthen be deployed in combination with fresh perceptions of objects,with which they may or may not accord, to produce beliefs. When one ofthese traces does not “fit” an incoming perception, like ashoe put on the wrong foot, the combination is incorrect and theresulting belief false (193c–194b).The model satisfies both constraints introducedby the earlier puzzles: it provides cases of falsehood where we arerelated exclusively to things that are, and where both items are insome way present to thought. But as Socrates develops the suggestion,it is made to rely crucially on our having different kinds ofcognitive access to the two items combined in the belief (memorytraces, on the one hand, and perceptions, on the other: 195c–d).As such, it doesnot serve to explain cases where just thoughts are involved, as whensomeone incorrectly believes that the sum of 5 and 7 is 11 (195e–196a).This isenough to vitiate the account Socrates and Theaetetus have given offalse belief. But there should no longer be an issue about whetherfalse beliefs arepossible, the challenge posed by theoriginal puzzles, only about whether we have been given afullycomprehensive account. Socrates tries to salvage the theory byproposing another model, where having different thoughts is comparedto grabbing at birds in an aviary (197c–200d).Here againthe constraints introduced by the earlier puzzles are met, but theaccount does not seem any more promising, if taken as a general theoryof false belief. It is soon given up after being subjected to a numberof objections, and Socrates returns to the dialogue’s mainconcern with knowledge.

TheTheaetetus does not have much to say about intentionalitymore broadly, in particular about the intentionality of theperceptions and thoughts that are combined in belief – thedialogue’s attention to these issues is limited, understandably,by the exigencies of the main argument. Perception had earlier beendismissed as not being in a position even to attain truth (186e),much less being capable of falsehood; but littleis said about how perceptual content should be understood. The finalsection of the dialogue briefly raises an important problem about theintentionality of thought, however, which is entirely distinct fromthe problems involving falsehood or nonexistence. If one has a truebelief about something, but not knowledge, and in particular does notgrasp how that thing differs from all other things, Socrates worries,then how does the belief manage to be about the very thing it is infact about? How can thoughts of general characteristics, that areshared equally by other things, “make me think of Theaetetusrather than of Theodorus, or of the most distant Mysian, as the sayinggoes?” (209b) This is an especiallyclear statement (in all likelihood the first) of what Chisholm wouldlater call “the problem of objective reference.” And hisreading of theTheaetetus may well be what lies behindWittgenstein’s own statement of the puzzle: “What makes myrepresentation of him a representation ofhim? Not thesimilarity of the image.” (Phil. Invest., II.177,§iii)

Plato offers a solution to the puzzles about falsehood in theSophist. It goes unchallenged in the text and may well havebeen regarded by him as definitive. (It need not be a recent discoveryon Plato’s part, as is often assumed; he needn’t have beenstumped by these puzzles himself when he composed the earlierpassages: see Burnyeat 2002.) In this dialogue, when the Eleaticvisitor introduces the puzzles about false belief and speakingfalsely, he points out the danger of contradicting oneself, invokingParmenides’ proscriptions against speaking of what is not(236e–237c). Buthe also insists that we must find a way of reconstruing such claims,if we are to show that falsehood is possible (240d–241b)withoutcommitting patricide against “Father Parmenides” (241d).The subsequent solution turns on recognizing acomplexity in the structure of statements, between the subject, whichis named in the statement, and what is said about it, as expressed bythe predicate (261d–262d).Statements are no longer thought of on the modelof names, which are true if they name something “that is.”Instead, for a statement to be meaningful, one part of it mustsuccessfully name something and the other say something about it,which may be either true or false of this. Something analogous willhold for belief, the visitor says, as belief is taken to be a kind ofinternal assertion made by the soul (263d–264b).As we haveseen, several features of this solution are already prefigured in theTheaetetus: both the requirement that thought and speech berelated only to what is, and the insight that the complexity ofstatements and beliefs allows for error to occur in a mismatch of theparts or a misapplication of one to the other. But it is only in theSophist that this mismatch is explicitly characterized interms of thedifference between things that are, rather thansimply being about “what is not.” A false statementasserts what is not the case regarding the subject, by stating thatthe subject isother than it in fact is (263a–d).The analysis intheSophist appears incomplete as it stands, though, since itonly applies to subject-predicate sentences, where the subjectsucceeds in referring to something (262e,263c): it is unclear how the visitor wouldhandle other types of statements, much less negative existentials(such as ‘there are no witches’). It also gives no accountof naming or nonpropositional attitudes. But, again, if we consideronly the original challenge posed by Parmenides and the Sophists,namely, to show that falsehood is possible, then Plato has clearlysucceeded in providing an answer.

5. Aristotle

Medieval theories of intentionality – not to mention more recentphilosophers influenced by these theories, such as Brentano (1874[1995]) – draw their inspiration from Aristotle’s theoryof perception and thought, in particular his doctrine that incognition the form of the sensible or intelligible object is“received without the matter” (On the Soul II 12,424a17–24; III 2, 425b23–24; III 4, 429a15–19; andIII 8, 431b26–29) and the doctrine that the object, or moreprecisely its activity as an object of cognition, is “one andthe same” as the activity of cognition and is present in thecognizing subject (III 2, 425b25–426a27). Both perception andthought are intentional states, and Aristotle’s analyses of themare central to his psychological theory as a whole. But none of thesepassages gives clear evidence of Aristotle’s awareness of theproblem of intentionality, much less provides a definition ofintentionality or any of its essential features. To begin with, eachdoctrine applies to more than just intentional states. The impressionof signet ring in sealing wax is offered not merely as an analogy, butas a genuine example of a form’s being received without thematter, a point accepted even by commentators such as John Philoponusand Thomas Aquinas; Philoponus also mentions images in mirrors asanother example (Philoponus,On Aristotle’s On theSoul, 444.17–26, 437.19–25; Thomas AquinasOnAristotle’s On the Soul 2.24, 56–59 = §554). Thisdoctrine cannot therefore provide a sufficient condition forintentionality, still less for cognition or awareness. Similarly,Aristotle defends his claim that the object’s activity is one andthe same as the activity of cognition and present in the cognizingsubject as simply an instance of a much wider causal generalization:in every causal interaction, including inanimate and noncognitiveones, the activity of the agent is one and the same as the activity ofthe patient and occurs in the patient (On the Soul III 2,426a2–11). Further, neither of these doctrines holds for allintentional states: each fails to apply to paradigmatic cases ofintentionality, like dreams or future hopes, where the problem ofintentionality is most palpable. So neither doctrine provides anecessary condition for intentionality either. They are rather generalcausal doctrines that apply to a special class of intentional states,like perception and thought, where the intentional state is about whatbrings it about – that is, it is about its own cause –something that is not true of intentional states in general. Even ifthey prove to be central to histheory of intentionality,they do not directly address the problem as such.

Aristotle is, however, keenly aware of the special character ofintentional states. In fact, he excoriates his predecessors forfailing to account for intentional states whose objects arenot the causes that bring them about. In the second chapterof his essayOn Memory and Recollection, he rejects the ideathat thought extends, like a ray, to its object, because we“think in the same way even when they do not exist”: insuch cases a ray will not work, since there won’t be anythingfor it to extendto (452b9–11). He goes further in hispolemicOn Ideas (81.25–82.1), when he rejects Platonictheories that take our thoughts to be of Platonic forms. Because suchobjects supposedly always exist, whether or not the individuals thatfall under them do, this sort of theory evades the previous criticism:given such intermediaries, thereis something thought canreach. But, Aristotle objects, they cannot account for the full rangeof thoughts we actually have, since we can think of particularindividuals who no longer exist, like Socrates, and mythical creaturesthat “do not exist in any way at all,” like thehippocentaur. In such cases, there is no Platonic form that can serveas the object of thought: by the Platonists’ own lights, thereis no form of Socrates or of Hippocentaur. So simply positing aspecial object of the same type as a Form won’t suffice.

Aristotle seems confident that his own theory has the resources todeal with both sets of counterexamples. He believes there are changesin our bodies thatrepresent ormodel the objects inquestion (without being instances of the exact same type), and byundergoing these changes we are able to have thoughts with therelevant contents, whether or not the corresponding objects exist inthe world at large. He describes such changes asphantasmata,a term often translated as ‘images.’ But while suchrepresentations are underlie imagistic experiences, such asvisualization and dreams, they also bear content in the absence ofsuch experience. Aristotle deploysphantasmata throughout hispsychology, both in cognitive states, like thought and memory, and indesires, passions, and action. The underlying capacity, which he callsphantasia, is formally introduced inOn the Soul III3 in response once again to the problem of intentionality. Accordingto Aristotle, his predecessors are unable to explain how error couldever take place. On their view, all cognition is about what brings itabout, such that “like is known by like,” and this, hebelieves, precludes the possibility of error (427a9–b6). But tothe extent Aristotle himself explains perception and thought alongsimilar lines, he will be vulnerable to the same criticism; andconsistent with this, he actually regards both states (at least intheir most basic forms, which we might call ’sensation’and ’understanding’) as incapable of falsehood. But unlikehis predecessors, Aristotle does not think thatall mentalstates are to be explained on this simple model. As he immediatelygoes on to argue,phantasia is a distinct kind of mentalstate that cannot be reduced to sensation, understanding, belief, oreven a combination of belief and perception (428a24–b9). Itconsists in perceptual traces, which are capable of affecting thecentral organ in the same way that perceptual stimulations do and socapable of producing similar experiences even in the absence of thecorresponding external objects. It is this, he claims, that makesfalsehood possible and so explains the actions and reactions ofanimals (428b10–429a8).

Thought, Aristotle insists, always requires aphantasma(On the Soul III 7, 431a16–17, b2; III 8,432a8–10;On Memory 1, 449b31). But the content of eventhe simplest concept goes beyond that contained in any suchquasi-perceptual representations (On the Soul III 8,432a12–14). At a minimum, in thought we are able to focusselectively on certain features, by ignoring many of the otherfeatures in such representations, just as we can use a diagram of atriangle for mathematical purposes without being concerned with itsparticular dimensions, and so effectivelyabstract them(On Memory 1, 449b31–450a17). But we are also capableof using one concept to form the opposite concept and of applying oneconcept to another to result in a compound propositional thoughtcapable of truth or falsehood (On the Soul III 6;Metaphysics VI 4, IX 10;On Interpretation 1). Theabstract content that results from such operations allows us to usesymbols to speak and understand one another (OnInterpretation 1, 16a3–9).

Aristotle also considers higher-order perception and thought. Heoffers a regress argument at the beginning ofOn the Soul III2 to show that when we perceive that we see or hear, we have ahigher-order perceptual awareness of the first-order perceiving(425b12–25) and, while the precise details are a matter ofcontroversy, it is arguably the same act of perception being directedat itself (Caston 2002b; for a response, see Johansen 2005).But Aristotle elsewhere claims that in general states like knowledge,perception, belief, or thought are always directed atsomethingelse primarily and themselves only peripherally or “on theside” (en parergōi); only God’sself-reflexive thinking, which he characterizes as a “thinkingof thinking” (noēsis noēseōs), hasitself as its primary object (Metaph. XII 9,1074b34–36). Self-directed intentionality raises a number ofquestions, in particular whether Aristotle is committed to it being apart ofevery mental act – as he seems to claim atNicomachean Ethics IX 9, 1170a29–b1, which Brentano1874 [1995], Book II, chs 2–4 takes up and champions – andwhether he thinks it is possible to be in error about the content orcharacter of the first-order state, even if not about its existence(Caston 2002b).

6. The Stoics

The earliest Stoics seem committed to preserving the intuition thatwhenever we are in a mental state,there is something thatour mental state is of or about. But they reject the Parmenideanrequirement that this must be something “that is”,something that exists or obtains. On the contrary, they claim that“in the nature of things, some things are and some arenot,” since the nature of things includes “anything thatcomes to mind, such as centaurs, giants or anything else made up by afalse thought.” (SenecaLetter 58.15) Accordingly,these Stoics regardSomething as the highest genus, ratherthanWhat is orWhat has being, as Plato had.Whenever aphantasia or representation is of something whichdoes not in fact exist, there still is something our representation isof, which they call aphantasma, an “apparition”or “figment”. Even though it does not exist, on this viewit is still something and so can serve as the object of our mentalstate.

This position does not seem to have to have arisen from idlespeculation, but rather as part of a response to Plato. The first twoheads of the school, Zeno of Citium and Cleanthes of Assos, argue thatthere are no such things as Plato’s forms. The concept(ennoia) of a kind, that is, of a genus or species, is athought of what they call anennoēma, an object that isquite literally “in a thought” (en +noēma), an “immanent object”, but is foundonly in thought. The precise nature of these objects iscontroversial. According to one source (Stobaeus, 1.136.21 ff.), theyare “not something” and so not somethingqualified in a certain way, but only “as if” they weresomething and “as if” they were qualified; they arefurther said to be only “apparitions” orphantasmata, something merely represented. On this basis,most interpretations take the Stoics to hold that the objects of thesethoughts are “not-somethings” (outina): fictionsor figments that are so beyond the pale, allegedly, that they do noteven countas something. But so understood, the Stoic viewwould be deeply obscure, if not actually incoherent. If the objects ofthese thoughts are not something, they are not anything, on pain ofcontradiction. That, after all, was the point of claiming thatSomething is the highest or most comprehensive genus:everything is something. But if there are no such things,then what is gained by replacing Platonic forms withennoēmata, rather than simply eliminating Platonic formsaltogether? Worse, what becomes of the intuition that whenever we havea representation, thereis something that our representationis of?

The earliest Stoics do think they have gained something by this move,though. They appeal, unsurprisingly, to both genera and species incharacterizing the methods of definition and division, which they taketo be central to logic and reasoning. Far from being a blank nothing,these objects are distinguished from one another in terms of theircommon features and differences, as they would have to be for theclassificatory system required for dialectic and science. The Stoics,moreover, explicitlyquantify over these objects: there is,in fact, a distinct object of thought for each number (PlotinusEnneads 6.6.12.13–29). In referring to them as“apparitions” (phantasmata), moreover, the Stoicsare not eliminating them. They are recognizing them as something thatour mind is directed towards whenever something general“appears” to us or is represented (phantasia).For as we have seen, they hold that whatever appears to usissomething, even if it is not something that exists or obtains.The natural move for the Stoics, then, would be to say that whilePlatonic forms aren’t anything at all – there areno such things – thereare such things asennoēmata; they just aren’t anything thatis, that exists or obtains. And in fact a parallel report inDiogenes Laertius can be read in precisely this way: although anennoēma is not anythingthat exists and so doesnot possess qualities, it is nevertheless “as if” it weresomethingthat exists and “as if” it possessedqualities, “like the impression of a horse when none ispresent” (Diogenes Laertius VII 61). In such a case, what Iimagine is something and indeed something horse–like; but it isnot a real horse or anything existent, and so on their view notsomething that can act or be acted upon and so not a body. It ismerely an object of thought.

Such generic objects will further be incomplete or indeterminate. Itwill not be true to say that the generic human (genikosanthrōpos) is Greek, for example, or equally to say that itis not Greek, even in an “as if” sort of way, since some,but not all, humans are Greek (Sextus Empiricus,Adv. math.VII 246). A generic object will be “as if” it wereF if, and only if,all the individuals falling underit areF. This claim need not violate the Principle of theExcluded Middle, since it would still be true of the generic humanthat it iseither Greekor not Greek, since it istrue that all humans are either Greek or not Greek. But it wouldviolate the Principle of Bivalence, since it still will be neithertrue nor false to say that the generic human is Greek. (For furtherdiscussion ofennoēmata, see Caston 1999.)

The third head of the school, Chrysippus of Soli, avoids theseproblems by appealing instead to “that which can be said”or “meant” (lekta, lit. ‘sayables’),certain abstract objects that are signified by our words.Lekta, like place, void, and time, cannot themselves eitheract or be acted upon, and so in the Stoics’ view cannot bebodies, which are the only existents they recognize; all such entitiesare instead classified as “incorporeals”(asōmata). Butlekta will still besomething, since in each case there is something that ourwords signify; it is just that they “subsist”(huphestanai) rather than exist (einai), as theStoics sometimes say. Unlikeennoēmata, however, theywill not generally be theobjects of mental states (exceptperhaps when we are thinking about Stoic semantics, for example). Theyserve rather as thecontents of mental states, which can bearticulated in language, regardless of which objects (if any) thesestates are directed towards (Sextus EmpiricusAdv. math. VIII11–12, 70, 409; Diogenes Laertius VII 63). There arelekta corresponding to general terms and predicates, as wellas to sentences of all kinds: not only to simple and molecularpropositions (axiōmata), but also questions, commands,oaths, suggestions, prayers, and so on (Sextus EmpiricusAdv.math. VIII 71–73; Diogenes Laertius VII 66–8). ForChrysippus, moreover, a definition like ‘a human is a rationalmortal animal’, should not be construed as being about a genericobject, even in an “as if” sort of way. Rather it has thesame meaning as the universal generalization, ‘if something is ahuman, then that thing is a rational mortal animal’ (SextusEmpiricusAdv. math. XI 8–11). But such a propositioncommits us to nothing more than the relevantindividuals thatsatisfy it (if indeed there are any) and to thelektasignified by its predicates. Finally, unlike generic objects,lekta are not indeterminate. It is simplyfalse toclaim that what is expressed by the predicate ‘is a human’is itself a human (and likewise simply true that the predicate‘is a predicate’ is itself a predicate). Therefore,lekta need not pose a threat to the Principle ofBivalence.

One of the most tantalizing questions concerns the relationshipbetween mental representations (phantasiai) andlekta. The Stoics effectively endorse a version ofBrentano’s Thesis that intentionality is the criterion of themental, which demarcates the domain of psychology. The Stoics thinkthat representations are what set animals and humans apart from plantsand inanimate substances: only things withpsuchē orsoul have mental representations (phantasiai) of the worldand make efforts (hormai) to move and change things (OrigenOn Principles 3.1.2, 196.12–197.8 Koetschau). But they alsothink that representations are a pervasive feature of psychologicalphenomena: every mental state either is a representation or involvesone essentially, because it is an assent to a representation ascorrect or rejection of it as incorrect or withholding assent from italtogether. So representation (phantasia) is a feature of alland only mental states.Lekta constitute the content of theserepresentations. The Stoics in fact define them as “what subsists incorrespondence with a rational representation,” where a rationalrepresentation is one that belongs to rational animals like ourselves(Diogenes Laertius VII 63; Sextus EmpiricusAdv. math. VII51).

This definition, though, also poses a difficulty. In recent decades,it has been thought to imply thatlekta subsistonlyin connection with the representations of rational animals –something not stated explicitly in our reports – even thoughthis would have problematic consequences: it would imply thatnonrational animals and indeed very young humans, before they developreason, would either paradoxically have representations without anycontent at all or solely with nonconceptual content that could not bearticulated. (For a classic statement of the view, see Frede 1983[1987], 153–54, 156; for a discussion of the consequences, seeSorabji 1993, 20–28.) Neither the Stoics nor their critics evermention such consequences, and it would make it difficult, if notimpossible, for them to account for animal behavior, much less theemergence of reason itself in humans. They insist that we have noconcepts (ennoiai) at birth, comparing the mind to a blanksheet of papyrus, ready to be written upon: it is first inscribed byperceptions and then subsequently, through the sorting and collectionof perceptual memories, by experience, issuing in our first naturalconcepts, from which we can later construct even more complexconcepts. Reason only appears later – some sources say at ageseven, others at fourteen – when there are sufficient conceptsto form a stable, interrelated system (Aetius 4.11.1–4; PlutarchOn Common Conceptions 1084f–1085a;DiogenesLaertius VII 53). So on the Stoics’ view, children will possessconcepts at some stagebefore they have reason, since reasonemerges from the cumulative acquisition and systematization ofconcepts, and evidently some of these concepts are formed naturallyfrom perceptions and memories alone, unaided by reason, from whichthey presumably derive their content at least in part. Since all thesestates undoubtedly possess content, there is no principled ground fordenying analogous content in the case of representations innonrational animals either, at least for perceptualrepresentations.

Iflekta serve here, as elsewhere, as the content of thesestates, thenlekta will not correspondsolely torational representations. But how, one might reasonably ask, can therepresenations in nonrational animals and very young humans, who arewithout concepts and incapable of articulate speech, havelekta corresponding to them? There is a widespread assumptionin the secondary literature that whether alekton correspondsto a representation depends upon which concepts (if any) an individualpossesses. But the Stoics cannot accept this assumption. Quite thecontrary. They believe that alekton is involved inevery causal interaction, whether animate or inanimate: onebody causes alekton to become true or hold of another body,where thelekton specifies the fully determinate effect ofthe agent on the patient (Stobaeus 1.138.14; Sextus EmpiricusAdv.math. 9.211; Clement of AlexandriaStromata8.9.3–4; this point is rightly emphasized by Frede 1994). Butthis analysis of causation immediately becomes pertinent once weacknowledge that the Stoics also hold a causal theory ofrepresentation: they define representations as the effect –literally, an “impression” (tupōsis) –that in the paradigmatic case the object of representation produces onthe soul (which on their view is a body); and they expressly comparethis to the impression a signet ring makes in wax (Diogenes LaertiusVII 50; Aetius 4.12.1–4; PlutarchOn Common Conceptions1084f–1085a),and they appeal to sigillary language again when they define the“secure” representation they regard as the criterion oftruth and foundation of knowledge (phantasiakatalēptikē), which represents the object that producesit in such rich detail that it could be distinguished from anythingelse, no matter how similar (CiceroAcad. 2.77–78; SextusEmpiricusAdv. math. 7.248 ff.; Diogenes Laertius VII46).

Whenever an object produces a representation, then, there will be acorrespondinglekton that specifies the object’s fullydeterminate effect on the soul: not only that it is a representationand a representation of a certain sort, but one that representsobjects in the world as having various features and standing invarious relations, potentially in extraordinarily rich detail.Embedded within this complexlekton will be a clause thatexhaustively expresses the content: if all suchlekta can becaptured with the schema, ‘… forms a representationthat –’, whatever fills the second blank will expressthe total content of the representation. None of this requires conceptpossession or even conceptual abilities: whichlekton belongsto a representation is determined causally by the interaction of aspecific object and a specific subject in certain conditions, so longas the subject is capable of forming a representation when affected byappropriate objects in the right way. Perceptual representations evenin nonrational animals will ordinarily have tremendously detailedcontents, which cannot be exhaustively expressed by a simpleproposition, as part of the correspondinglekton. Humans cango further than nonrational animals, though, through their ability tofocus selectively on individual parts of such content and responddifferentially, assenting to some, rejecting others, and withholdingassent on still others. This ability to consider isolated contents iswhat allows rational animals to entertain abstract representations,whose total contentcan be expressed by a simple proposition;or indeed to entertain any content formed by logical operations uponthese (possibly recursively). It is therefore only by reference to thecontents of rational representations that we are able to capture thefull domain oflekta, much as the definition in DiogenesLaertius and Sextus Empiricus suggests, so as to include abstract aswell as perceptual representations. But this does not excludenonrational animals from also havinglekta corresponding totheir representations, thus making intentional explanations of theirbehavior possible and psychology more generally. (For more on Stoicrepresentations and a fuller defense of the interpretation above, seeCastonforthcoming.)

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