Philosophical skepticism is interesting because there are intriguingarguments for it despite its initial implausibility. Many contemporaryepistemological positions can be fruitfully presented as responding tosome aspect of those arguments. For example, questions regardingprinciples of epistemic closure and transmission are closely relatedto the discussion of what we will call Cartesian Skepticism, as areviews according to which we are entitled to dismiss skepticalhypotheses even though we do not have evidence against them. Thetraditional issue of the structure of knowledge and justification,engendering Foundationalism, Coherentism, and Infinitism, can be seenas resulting from one main argument for what we will call PyrrhonianSkepticism. In what follows we present these two forms of skepticismand assess the main arguments for them.

• 1. Knowledge, Justification and Skepticism
• 2. Two Basic Forms of Philosophical Skepticism
• 3. The Argument for Cartesian Skepticism Employing the Closure Principle
  • 3.1 Consideration of CP1
  • 3.2 Consideration of CP2
• 4. Contextualism
• 5. Pyrrhonian Skepticism
  • 5.1 Rejecting Premise 2: Foundationalism
  • 5.2 Rejecting Premise 5: Infinitism
  • 5.3 Rejecting Premise 3: Coherentism
  • 5.4 Rejecting Premise 7: Positism
  • 5.5 Rejecting More than One Premise
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Knowledge, Justification and Skepticism

Philosophically interesting forms of skepticism claim that we do notknow propositions which we ordinarily think we do know. We shoulddistinguish such skepticism from the ordinary kind, the claim that wedo not know propositions which we would gladly grant not to know.Thus, it is a form of ordinary skepticism to say that we do not knowthat there are an even number of stars in the Milky Way, but it is aform of philosophical skepticism to say that we do not know that thesun will come out tomorrow. Even though our interest is inphilosophical skepticism, we can start our inquiry by thinking aboutordinary skepticism.

Why do we readily grant, then, that we don’t know that there arean even number of stars in the Milky Way? To begin with, the vastmajority of us do not even believe that proposition, and it is widelyacknowledged that knowledge requires belief.^[1] But even those who believe it do not know it, even if they luck outand it is true. They do not know it because they are notjustified in believing it, and knowledge requires justification.^[2] Of course, they are not justified in disbelieving that propositioneither. Belief and disbelief are two of the so-calleddoxasticattitudes that we can adopt towards a proposition. We can also,of course, not even consider a proposition, and thus not adopt anydoxastic attitude towards it. But most philosophers would hold that inaddition to belief and disbelief there is a third possible doxasticattitude that we can adopt towards a proposition: we cansuspendjudgment (or withhold assent) with respect to it. Suspension ofjudgment is thus abona fide doxastic attitude alongsidebelief and disbelief, and is not to be equated with the failure toadopt any doxastic attitude.^[3] Because it is a genuine doxastic attitude, suspension of judgment(just like belief and disbelief, and unlike the failure to form anydoxastic attitude) can itself be justified or unjustified. Forinstance, we would ordinarily think that suspension of judgment isnot justified with respect to the proposition that Paris isthe Capital of France, but it is with respect to the proposition thatthere are an even number of stars in the Milky Way.

Some arguments for philosophical skepticism target knowledge directly,not concerning themselves with justification. For instance, some arguethat we do not know certain propositions because our beliefs in themare notsensitive (in a sense to be explained below), andthey claim that sensitivity is a condition on knowledge—butperhaps not on justified belief. We will examine the bearing of thesensitivity condition on skeptical arguments assuming that it appliesto justification. But even if an argument for philosophical skepticismtargets our knowledge in a certain area while remaining silent aboutwhether we have justified beliefs in that area, that argument willstill indirectly target our justification as well. For, if theargument succeeds, then it provides us with knowledge (or at leastjustified belief) that we do not know a certain propositionp.And it is plausible to hold that if we know (or justifiably believe)that we do not know a propositionp, then we are not evenjustified in believingp.

In what follows, then, we identify skepticism with respect to a fieldof propositionsF as the claim that the only justified attitudewith respect to propositions inF is suspension of judgment.Philosophical skepticism, then, differs from ordinary skepticism atleast regarding the field of propositions to which it is claimed toapply. But even within the realm of philosophical skepticism we canmake an interesting distinction by appealing to the scope of thethesis.

2. Two Basic Forms of Philosophical Skepticism

One interesting distinction between kinds of philosophical skepticismpertains to the question whether they iterate. Thus, considerskepticism about the future: the claim that the only justifiedattitude with respect to propositions about the future is suspensionof judgment. That kind of philosophical skepticism overlaps partlywith ordinary skepticism about the future. We should all grant, forinstance, that we should suspend judgment with respect to theproposition that the flip of this fair coin in the next second willcome up heads, but most of us think that we should believe, notsuspend judgment with respect to, the proposition that the sun willcome out tomorrow. Being a skeptic with respect to the first-orderproposition that the sun will come out tomorrow (that is to say,holding that the only justified attitude with respect to thatproposition is suspension of judgment) can be combined with any of thethree doxastic attitudes with respect to the second-order propositionthat the only justified attitude with respect to the proposition thatthe sun will come out tomorrow is to suspend judgment. Generalizing,whenever the skeptic holds that the only justified attitude withrespect to a field of propositionsF is to suspend judgment, wecan ask them which attitude is justified with respect to theproposition that the only justified attitude with respect to anyproposition inF is suspension of judgment. Perhaps the moststraightforward answer here is that the only justified attitude withrespect to that second-order proposition is belief. After all,isn’t skepticism with respect toFprecisely thebelief that we should suspend judgment with respect to any propositioninF? We will call this combination of views—the viewthat we should suspend judgment with respect to any proposition inF and believe the proposition that we should suspend judgmentwith respect to any proposition inF—“CartesianSkepticism”, because of the skeptical arguments investigated byDescartes and his critics in the mid-seventeenth century. Otherphilosophers, following an ancient tradition, refer to this view as“Academic Skepticism” (see the entry onancient skepticism).

But some skeptics are skeptics regarding second- (and higher-) orderpropositions as well as regarding first-order propositions. Followingthe same ancient tradition, we will call that kind of skepticism“Pyrrhonian Skepticism”. Without any claim to historicalaccuracy, we will take Pyrrhonian Skepticism to be absoluteskepticism—the thesis that suspension of judgment is the onlyjustified attitude with respect toany propositionp.Is Pyrrhonian Skepticism so understood self-refuting? It is certainlyformally consistent: no contradiction follows just from thepropositions that the only justified attitude with respect to theproposition thatp is suspension of judgment and that the onlyjustified attitude with respect to the proposition that the onlyjustified attitude with respect to the proposition thatp issuspension of judgment is suspension of judgment (say that three timesfast!). But consider the principle that whenever someone is committedto a propositionp they are also (perhaps implicitly) committedto the proposition that belief is the (or at least a) justifiedattitude towardsp. Call this the “Commitment IterationPrinciple”. If the Commitment Iteration Principle holds, thenPyrrhonian Skepticism is indeed self-refuting. For Pyrrhonian skepticsare committed to the claim that suspension of judgment is the onlyjustified attitude with respect to some propositionp. By theCommitment Iteration Principle, they are then committed to the claimthat belief is a justified attitude with respect to the propositionthat suspension of judgment is the only justified attitude withrespect top. Therefore, if they are in addition committed tothe claim that suspension of judgment is the only justified attitudewith respect to that very same proposition, they are committed to aninconsistent set of propositions. But Pyrrhonian skeptics need nothold the Commitment Iteration Principle. Indeed, they are committed tothinking that suspension of judgment is the only justified attitudewith respect to the Commitment Iteration Principle itself (and alsowith respect to analogous principles which may make trouble forPyrrhonian Skepticism). Of course, Pyrrhonian Skepticism will not beacceptable to anyone who does hold the Commitment IterationPrinciple—but neither will Pyrrhonian Skepticism be acceptableto anyone who holds that we should not suspend judgment with respectto some proposition. It is not clear, then, that the charge ofself-refutation represents an independent indictment of PyrrhonianSkepticism. In any case, contemporary philosophers find PyrrhonianSkepticism interesting not because they take seriously the possibilityof its truth, but rather because there are interesting arguments inits favor, the responses to which shape the contours of manycontemporary epistemological theories.

We have distinguished between Cartesian and Pyrrhonian Skepticism, butwe have characterized both views in terms of a generic field ofpropositionsF. In the case of Pyrrhonian Skepticism,Fincludes every proposition, but we can generate different versions ofCartesian Skepticism by varyingF. A prominent version ofCartesian Skepticism is external-world skepticism—i.e.,Cartesian Skepticism with respect to any proposition about the“external world” (not about the subject’s own mind).^[4] In what follows, we concentrate on external world CartesianSkepticism and Pyrrhonian Skepticism.

3. The Argument for Cartesian Skepticism Employing the Closure Principle

Many contemporary philosophers take the canonical argument forCartesian Skepticism to involve skeptical hypotheses and a ClosurePrinciple (CP).^[5] A skeptical hypothesis (with respect to a propositionp and asubjectS) is a propositionSH such that ifSHwere true, then: (a)S would not knowp, and (b)S would not be able to distinguishSH from a situationwhereS knowsp. The evil demon scenario that Descartesenvisions at the end of his “First Meditation” functionsas a near-universal skeptical hypothesis, for the demon has the powerto deceive any subject regarding almost any proposition. One way inwhich aSH may satisfy (a) is by describing a situation wherep is false, but this is not the only way. Descartes’ evildemon may induce in a disembodied subject’s mind an experienceas of the subject’s own hands in front of her, as a result ofwhich the subject believes that there are hands in front of her, whileat the same time dangling some unattached hands in front of thesubject (we are waiving here difficulties having to do with how tolocate objects relative to disembodied subjects). The subject’sbelief that there are hands in front of her is in that case true, butshe still doesn’t know it. The connection between Closureprinciples and arguments for skepticism gets complicated if wecountenance skeptical hypotheses which do not entail the falsehood ofthe proposition in question, and so in what follows we limit ourdiscussion to those that do.

Letting “h” stand for any proposition about theexternal world we would ordinarily take ourselves to be justified inbelieving, for example, G. E. Moore’s famous “here’sa hand” (Moore 1939 [1993]), and re-using “SH” for askeptical hypothesis relative toh (we leave the subjecttacit), we can state the contemporary canonicalCP-style argumentfor Cartesian Skepticism as follows:

CP1 follows from the following Closure Principle (letting“Jx” stand forthe subject is justified inbelievingx):

(In the argument above, \(x = h\) and \(y = {\sim}SH\).)

A crucial feature of CP is that it does not depend upon employing astringent notion of justification. Suppose that (positive)justification comes in degrees, where the lowest degree is somethinglike mere plausibility and the highest degree is absolute certainty.CP could be recast as follows:

There appear to be only three ways that one can respond to theCP-style skeptical argument: deny at least one premise, deny that theargument is valid, or reluctantly accept the conclusion—ifneither of the first two alternatives succeeds.

3.1 Consideration of CP1

Let us begin an examination of CP1 and the general closure principle,CP, of which CP1 is an instantiation. Closure certainly does hold forsome properties, for example, truth. Ifp is true and impliesq, thenq is true. It just as clearly does not hold forother properties, for example being surprising. It might be surprisingthat Tomás is taller than his father, but it is certainly notsurprising that Tomás is taller than someone, and yet theformer entails the latter. What about justified belief? Does Closurehold for it?

It might be thought that the answer must be a clear “No”,for the following reasons. First, notice that every logical truth isentailed by every proposition. If Closure held for justification, thenwe would have to say that everybody is justified in believing everylogical truth (provided that we are willing to grant that everybody isjustified in believing at least one proposition). But thisdoesn’t seem plausible. Some logical truths are too complicatedto even parse, let alone be justified in believing. If this is true,then Closure doesn’t hold for belief (that is to say, we mayfail to believe propositions entailed by propositions we alreadybelieve). The existence of very complicated logical truths alsounderlies another worry for Closure. For to every logical entailmentbetween propositions there corresponds a logical truth: the (material)conditional with the entailing proposition in the antecedent and theentailed proposition in the consequent. Some of these logically trueconditionals will be examples of propositions that we are notjustified in believing (if only because the consequent is toocomplicated for beings like us to even parse). In that case, we mightwell be justified in believing their antecedents without beingjustified in believing their consequents.

But it also appears that CP can easily be repaired. We can stipulate(i) that the domain of the propositions in the generalization of CPincludes only contingent propositions that are withinS’scapacity to grasp and (ii) that the entailment is“obvious” toS. The skeptic can agree to thoserestrictions because the skeptical scenarios are posited in such a wayas to render it obvious that our ordinary beliefs are false in thosescenarios, and it is taken to be a contingent claim thatS isin the actual circumstances as described in the antecedent. (For afull discussion of the required repairs of CP, see David &Warfield 2008 and Hawthorne 2014.)

There is one other important, required clarification of the restrictedversion of CP. “Justified belief” is ambiguous. It couldbe used to refer to a species of actually held beliefs—namely,those actually held beliefs ofS that are justified. Or itcould refer to propositions thatS is justified inbelieving—regardless of whetherS does indeed believethem. Following Roderick Firth, the distinction between actually heldjustified beliefs and propositions one is justified in believing,regardless of whether they are actually believed, is often marked bydistinguishing between doxastic and propositional justification (seeFirth 1978). If CP is to be acceptable, “justified inbelieving” in the consequent must be used so as to refer topropositional justification for a reason already cited, i.e., thatClosure does not hold for belief. In other words, one ofS’s actual beliefs,p, might be justified andS still fail to believe some proposition that is entailed byp.^[6]

We are now in a position to ask: Does the restricted form of closurehold? There are at least three types of argument against closure inthe literature: alleged counterexamples, alleged unpalatableconsequences, and incompatibility with allegedly plausibleepistemological theories. In the remainder of this section we examineone exemplar of each of these.

Fred Dretske and others have produced cases in which they believe CP fails.^[7] Dretske writes:

You take your son to the zoo, see several zebras, and, when questionedby your son, tell him they are zebras. Do you know they are zebras?Well, most of us would have little hesitation in saying that we didknow this. We know what zebras look like, and, besides, this is thecity zoo and the animals are in a pen clearly marked“Zebras.” Yet, something’s being a zebra impliesthat it is not a mule and, in particular, not a mule cleverlydisguised by the zoo authorities to look like a zebra. Do you knowthat these animals are not mules cleverly disguised by the zooauthorities to look like zebras? If you are tempted to say“Yes” to this question, think a moment about what reasonsyou have, what evidence you can produce in favor of this claim. Theevidence youhad for thinking them zebras has beeneffectively neutralized, since it does not count towardtheirnot being mules cleverly disguised to look likezebras. (Dretske 1970: 1015–1016)

Dretske is speaking of knowledge rather than justified beliefs, butthat seems irrelevant since the issue concerns the supposed lack of asufficient source of evidence or reasons for the claim that the animalis not a cleverly disguised mule.

The crucial thing to note about this proposed counterexample is thatit works only if the Closure Principle entails that the very samesource of evidence that justifiesS in believing that theanimals are zebras must justifyS in believing that they arenot cleverly disguised mules. Since the evidence for the former hasbeen “effectively neutralized”, it is not available forthe latter. Now, in response one could claim that once the question ofwhether the animals are disguised mules has been raised, the evidenceis “effectively neutralized” for both the former and thelatter, andS is no longer justified in believing that theanimals are zebras. Thus, it could be held that this example couldactually be used to support CP. Nevertheless, let us grant that theevidence for the claim that the animals are zebras cannot be used toshow that they are not cleverly disguised mules. Still, it could beargued that this would not force giving up CP.

Such an argument could begin by recalling that CP claimed merely thatwhenever a subject is justified in believingp, then thatsubject is justified in believingq. CP does not require thatthe subject have the same evidence forp as she does forq. Dretske’s purported counterexample seems to requirethat CP implies that the adequate source of evidence is the same forboth propositions.

No doubt this constraint sometimes correctly portrays the relevantevidential relationships when some proposition entails some otherproposition. For example, suppose I have adequate evidence for theclaim that Anne has two brothers. Then it would seem that the verysame evidence would be adequate for believing that Anne has at leastone brother. But the defender of CP, and more particularly theCartesian Skeptic, could point out that closure does not require thisto hold for every case.

There are two other possibilities. First, one may hold that whenp entailsq and there is some evidencee forp, it isp itself that is evidence forq. Forexample, it may be held that given that I have adequate evidence forbelieving that 2 is a prime number, I can use that very proposition(that 2 is a prime number) as an adequate reason for believing thatthere is at least one even prime. (See Klein 1981, 1995, and 2000, butsee below for reasons for doubting that this is a genuinepossibility.) Second, there are cases where the order is reversedbecauseq serves as part of the evidence forp. Forexample, suppose that I am justified,ceteris paribus, inbelieving that (pure) water is present if I am justified in believingthat there is present, at standard temperature and pressure, a clear,odorless, watery-tasting and watery-looking fluid that containshydrogen and oxygen. This pattern is typical of abductive inferences,and is often referred to as “inference to the bestexplanation”. (See Vogel 1990, 2014b for a discussion of Cartesian Skepticism and inference tothe best explanation.) In addition, there are cases in which it seemsthat some contraries ofh need to be eliminated prior toh’s being justified. For example, reconsidering thezebra-in-the-zoo case, it seems to be true that if I had some goodreason to think that the animals are cleverly disguised mules, such acontrary would need to be eliminated before I would be justified inbelieving that the animals were zebras.^[8]

It could also be argued that CP has unacceptable consequences. Ofcourse, one of those unacceptable consequences may well be CartesianSkepticism itself, but to point that out in the present context wouldbe dialectically unhelpful. It has been argued, however, that CP byitself has far-reaching skeptical consequences. Notice that theargument for Cartesian Skepticism under consideration contains CP2 asan essential premise. The present concern is that CP by itself (andtherefore CP1, if justified on the basis of CP), without help fromCP2, has skeptical consequences. If that were true, that would be areason to be wary of CP, for it would be a much stronger principlethan advertised.

The argument can be presented as a conflict between CP, on the onehand, and three other principles. Those three other principles are,allegedly, beyond reproach, and so CP is to be blamed for theconflict. The first principle in question may be thought of asenshrining the possibility of knowledge (and justification) byampliative inference:

Ampliativity would be true if, for example, we can be justified inbelieving the conclusion of an inductive argument (say, that allemeralds are green) on the basis of believing its premises (say, thata properly selected group of emeralds have been observed to be green),without in addition being independently justified in believing anyother proposition which, together with those premises, entails theconclusion (such as, for example, the proposition that if a properlyselected sample of emeralds have all been green, then all emeralds aregreen).

The next principle is in conflict with what we presented above as analternative possibility to Dretske’s interpretation of theevidential structure of CP. Dretske’s counterexample works, wesaid, only if CP holds that whatever justifies the subject inbelievingp is also what justifies her in believingq.But there are two other possibilities. Maybe the evidential relationis reversed: whatever justifies us in believingq justifies usin believingp. Or maybe, we said,p itself, and notwhatever justifies us in believingp, justifies us in believingq. The next principle goes directly against thispossibility:

We call the principle “Mere Lemmas” because the ideabehind it is that if a proposition is a mere lemma, in the sense thatit derives all of its justification from some prior evidencee,then it doesn’t have justificatory powers of its own,independent of the justificatory powers ofe. Suppose, forinstance, that you start out by knowing that Jim has a pet, but youdon’t know what kind of pet it is (the example is from Pryor2004). Then you come to know that it is a hairless pet. Now you becomejustified (perhaps to a small degree) in believing that Jim’spet is a hairless dog. That is to say, whatever degree ofjustification you had before to believe that Jim’s pet is ahairless dog, you are now somewhat more justified in believing thatsame proposition. That Jim’s pet is a hairless dog of courseentails that Jim’s pet is a dog. But your justification forbelieving that Jim’s pet is a hairless dog cannot in any way betransmuted into justification for believing that Jim’s pet is adog. Whatever degree of justification you had before for believingthat Jim’s pet is a dog, you are now less justified in believingthat same proposition (because hairless dogs are a small minority ofhairless pets).

But what about the example with which we introduced the idea that,sometimes, whene is evidence forp, thenpitself can be evidence forq? The example was the following: wecan have adequate evidence for believing that 2 is a prime number, andthen that proposition itself (that 2 is a prime number) can justify usin believing that that there is at least one even prime number. But,when examined more closely, this is not an obvious counterexample toMere Lemmas. For, what could our adequate evidence that 2 is a primenumber be? Presumably, it would be that 2 is divisible only by 1 and2. That just is the definition of what it means for 2 to be a primenumber, however, so some may balk at the idea that it counts asevidence for the proposition in question (rather than being identicalwith it). In any case, it would not count as a counterexample to MereLemmas. For if we have no evidence for the proposition that 2 is aprime number, then the condition for the application of Mere Lemmas isnot satisfied.^[9] If, on the other hand, our evidence is that 2 is divisible only by 1and 2, then that proposition itself is obviously evidence for theproposition that an even number is prime.

Our final principle is the following:

The idea behind this principle is that ifp entailsq,then shouldq turn out to be true then things are aspsays they are, and so we can hardly useq as evidence againstp. We return to Entailment below, but first we show how thesethree principles are in conflict with CP.

Assume, with Ampliativity, that a subjectS is justified inbelieving a propositionh on the basis of some evidencee without having independent justification for believing anyother propositionp such thatp together witheentailsh. Notice thath obviously entailsh ornot-e. Therefore, by CP,S is justified in believinghor not-e. But, of course,e together withh ornot-e entailsh. Therefore, ifS is justified inbelievingh on the basis ofe, then there is aproposition whichS is justified in believing and whichtogether withe entailsh.

Notice that this is close to, but not quite, the negation ofAmpliativity. For Ampliativity denies that there will be any suchproposition whichS isindependently justified inbelieving, and for all we have saidS’s justification forbelievingh or not-e is not independent. Independent of what?OfS’s justification for believingh itself. Forall we have said so far,S might be justified in believingh or not-e on the basis ofh, or on the basis ofe itself.

But, given Mere Lemmas,h cannot justifyS in believingany proposition unlesse does. Therefore, the only option leftopen, short of denying Ampliativity, is to argue thate itselfjustifiesS in believingh or not-e. But that isincompatible with Entailment. For notice that fore to justifyS in believingh or not-e is fore to justifyS in disbelieving its negation, i.e.,e and not-h.But, of course,e and not-h entailse, and so theentailment principle has it thate cannot justifyS indisbelievinge and not-h—i.e.,e cannot justifyS in believingh or not-e.

Although this particular reconstruction is our own (for more on it,see Comesaña forthcoming), some philosophers have takenarguments similar to it to count against CP (see, for example, Huemer2001 and Sharon & Spectre 2017, and cf. Comesaña 2017).However, others have argued against Entailment (see, for example,Pryor 2014a,b and Vogel 2014b), and yet others have argued that denying Ampliativityitself is not as absurd as it might sound (Comesaña 2014a,b).The argument cannot, therefore, be taken to be a conclusive blowagainst CP.

Finally, some epistemological theories are in conflict with CP.^[10] Robert Nozick’s account of knowledge is the best such example.Roughly his account is this (Nozick 1981: 172–187):

S knows thatpiff:

1. S believesp;
2. p is true;
3. ifp were true,S would believep;
4. ifp were not true,S would not believep.

Nozick called his account a “tracking” account ofknowledge because wheneverS knows that \(p, S\)’sbeliefs trackp. Think of a guided missiletrackingits target. If the target were to move left, the missile would moveleft. If the target were not to move left, the missile would not moveleft. According to the tracking account of knowledge our beliefs musttrack the truth if we are to have knowledge.

There is one important clarification of conditions 3 and 4 that isdiscussed by Nozick, namely, that the method by whichSacquires the belief must be held constant from the actual world to thepossible world. A doting grandmother might know that her grandchild isnot a thief on the basis of sufficiently good evidence, but wouldstill believe that he wasn’t a thief, even if he were, becauseshe loves him. So, we must require that the grandmother use the samemethod in both the actual and the near possible worlds, for,otherwise, condition (4) would exclude some clear cases of knowledge.This is not the place to provide a full examination of Nozick’saccount of knowledge.^[11] What is crucial for our discussion is that it is easy to see that, ifNozick’s account is correct, closure will fail for knowledge injust the kind of case that the Cartesian Skeptic is putting forwardbecause of condition (4). SupposeS knows that there is a chairbefore her. Would she know that she is not in a skeptical scenario inwhich it merely appears that there is a chair? If the fourth conditionwere a necessary condition of knowledge, she would not know thatbecause if she were in such a scenario, she would be fooled intothinking that she wasn’t. Thus, either condition (4) is toostrong or CP fails.

There are some reasons for thinking that condition (4) is too strong.Consider, for instance, this case in the literature: You put a glassof ice-cold lemonade on a picnic table in your backyard. You go insideand get a telephone call from a friend and talk for half an hour. Whenyou hang up you remember that you had left the ice-cold lemonadeoutside exposed to the hot sun and come to believe that it isn’tice-cold anymore. It would seem that you could know that. Indeed, ifit were false, that could only be due to some bizarre circumstance.Thus, if the lemonade were still ice-cold, you would believe that itwasn’t (see Vogel 1987: 206). The moral of this (and similar)cases seems to be that sensitivity is not a correct condition onknowledge.

There is much more to say about CP and CP1, but we will move on toconsidering the argument’s other premise.

3.2 Consideration of CP2

CP2 claims that we are not justified in denying the skepticalhypothesis—in other words, that we are not justified inbelieving that we are not being deceived. What arguments can be givenfor CP2? It is tempting to suggest something like this: The skepticalscenarios are developed in such a way that it is assumed that wecould not tell that we were being deceived. For example, weare asked to consider that there is an Evil Genius “sopowerful” that it could (1) make me believe that there werehands when there were none and (2) make it such that Icouldnot detect the illusion. But the skeptic must be very careful here.She cannot require that in order forS to know (or be justifiedin believing) something, sayx, that ifx were false,she would not still believex. We have just seen (whileexamining Nozick’s account of knowledge) that this requirementis arguably too strong. So the mere fact that there could be skepticalscenarios in whichS still believes that she is not in such ascenario cannot provide the skeptic with a basis for thinking that shefails to know that she is not (actually) in a skeptical scenario. Buteven more importantly, were that a requirement of knowledge (orjustification), then we have seen that closure would fail and,consequently, the basis for the first premise in the CP-style argumentfor Cartesian Skepticism would be forfeited.^[12]

Ernest Sosa has argued for three interrelated theses regarding CP2 andNozick’s sensitivity condition: (i) that sensitivity can beeasily confused with a different condition on knowledge (which Sosacalls safety); (ii) that while sensitivity is not a correct necessarycondition on knowledge, safety is; (iii) finally, that our belief inthe negation of skeptical hypotheses is safe despite being insensitive.^[13]

Nozick’s sensitivity condition is asubjunctiveconditional: ifp were false,S would not believeit. The usual way in which such conditionals are evaluated is byassuming that there is an ordering ofpossible worldsaccording to how much they resemble the actual world. A subjunctiveconditional \(A \rightarrow B\) is true if and only ifB istrue in the closest (or all the closest) possible worlds whereA is true. According to this semantics, subjunctiveconditionals do not contrapose (the contrapositive of a conditionalif A, B isif not-B, not-A). Thus, suppose that weflip a coin to decide whether you or I will strike this match: headsyou strike it, tails I do. The coin comes up head, you strike thematch and it lights. In this situation, it is true that if I hadstruck the match, it would have lit. But it doesn’t seem to betrue that if the match hadn’t lit then I wouldn’t havestruck it. The match might have failed to lit because it was wet whileeither of us struck it. In the possible worlds terminology, theclosest possible world where I strike the match is a world where itlights, but there are possible worlds where the match doesn’tlight and I strike it that are as close to actuality as are worldswhere the match doesn’t light and you strike it.

After noticing the failure of subjunctives to contrapose, Sosaproposed that we should replace Nozick’s sensitivity conditionwith its contrapositive, which Sosa calls a ‘safety’condition. The following formulation seems to capture Sosa’sintent:

Now, one initial worry about safety as a condition on knowledge isthat, given that belief and truth are also necessary for knowledge,safety will always be (in this context) a true-true conditional (thatis to say, both its antecedent and consequent will be true). Thismeans that Sosa cannot accept the possible worlds semantics forsubjunctive conditionals briefly sketched above, at least if we assumethat every world is closer to itself than any other word. For when wehave a true-true conditional, the closest world where the antecedentis true will be the actual world, and so every such conditional willbe true (and, hence, any condition formulated by such conditionalswill be trivially satisfied).^[15] Rather, Sosa understands the truth-conditions for the relevantconditions as requiring that the consequent be true in all nearbypossible worlds where the antecedent is true.

Sosa’s idea, then, is that we can explain away the temptation tothink that CP2 is true by noticing that although safety andsensitivity are easily confused with one another, my belief that I amnot the victim of a skeptical scenario is insensitive but safe, andthat whereas sensitivity is not a condition on knowledge, safetyis.

But is safety a condition on knowledge? Several authors have thoughtthat, just as there are counterexamples to sensitivity, there arecounterexamples to safety as well. Here is one (taken fromComesaña 2005b):

Halloween Party: There is a Halloween party atAndy’s house, and I am invited. Andy’s house is verydifficult to find, so he hires Judy to stand at a crossroads anddirect people towards the house (Judy’s job is to tell peoplethat the party is at the house down the left road). Unbeknownst to me,Andy doesn’t want Michael to go to the party, so he also tellsJudy that if she sees Michael she should tell him the same thing shetells everybody else (that the party is at the house down the leftroad), but she should immediately phone Andy so that the party can bemoved to Adam’s house, which is down the right road. I seriouslyconsider disguising myself as Michael, but at the last moment Idon’t. When I get to the crossroads, I ask Judy where the partyis, and she tells me that it is down the left road.

That case is a counterexample to safety insofar as we agree that Iknow that the party is at the house down the left road, and yet itcould very easily have happened that I have that same belief on thesame basis without it being so that the belief was true.

So far, we have argued that there are dangers in defending CP2 byappealing to the sensitivity condition, and that Sosa’s attackon CP2 might itself be subject to doubt. What else can be said for oragainst CP2?

Let’s go back to the rough idea that there is some kind ofepistemic symmetry between what we take to be the actual case and askeptical scenario. Of course, if we were the victims in a skepticalscenario, we wouldn’t know that we are not (if only because itwould be false, but perhaps not only because of that). Given symmetry,even if we are not victims of a skeptical scenario, we do not knowthat we are not. Moreover, we know all of this. As we suggested insection 1, if we know that we don’t know thatp, then weare not even justified in believing thatp. Therefore, CP2.Every step in this argument can be challenged, but there is no doubtthat many philosophers find something along these lines at least worththinking about. Let us take a closer look at the first step, the claimthat there is an epistemic symmetry between the good case and theskeptical scenario.

What can this alleged symmetry amount to? One idea is that we have thesame evidence in both cases. According to a Cartesian account of thiscommon evidence, it consists in mental states of the subject, such asher experiences. By construction, the subject has the same experiencesin the skeptical scenario as she does in the good case. But somephilosophers, most notably Williamson 2000, have denied that we havethe same evidence in the good and the skeptical case. According toWilliamson, our evidence is constituted not by our experiences, but bywhat we know. Given that in the good case we know more propositionsthat in the bad case, we have more evidence in the good case than wedo in the skeptical case. In the good case, for instance, we knowmundane propositions such as the proposition that we have hands. Giventhat knowledge entails justification, in the good case we arejustified in believing that we have hands. Given CP, in the good casewe are justified in believing that we are not in the skeptical case.This account of evidence entails that the relation ofindiscriminability between the good case and the skeptical case is notsymmetric: victims of a skeptical scenario cannot distinguish theskeptical scenario from the good case (for all they know, they are inthe good case, and for all they know, they are in the skeptical case),but subjects in the good case can distinguish between the cases (theyknow that they are in the good case, and—again, givenCP—they know that they are not in the skeptical case).^[16]

But even those contemporary philosophers who grant that our epistemicposition with respect to external world propositions is the same inthe normal case as in the skeptical scenario can object to thesymmetry thesis. For even granting (as we must) that in the skepticalscenario we do not know that we are not in the skeptical scenario, itdoesn’t follow that in the ordinary case we do not know that weare not in the skeptical scenario, not even assuming that we have thesame evidence in both cases. To begin with, an obvious differencebetween the normal case and the skeptical scenario is that in theskeptical scenario the proposition in question (that we are not in theskeptical scenario) is false, whereas in the normal case it is true.Given that knowledge requires truth, we can explain why we lackknowledge in the skeptical scenario by appealing to this truthcondition on knowledge, rather than to the paucity of our evidence. Inother words, our evidence for thinking that we are not in theskeptical scenario, this reply holds, is good enough to know thatproposition, if only it were true. Now, the skeptic can then replythat not all skeptical scenarios are such that external worldspropositions are false in them. For instance, if I am right nowdreaming that I have hands I do not thereby know that I have hands,even though I do have hands while dreaming. We noted above that theintroduction of skeptical hypotheses which do not entail the falsityof external world propositions complicates the CP argument, but let ushere bracket that issue. For, in addition to truth, knowledgeplausibly requires other non-evidential conditions. In the wake of theGettier problem, for instance, many philosophers have accepted thatbesides belief, justification and truth, the right kind of relationbetween the truth of the proposition and the belief must hold, andarguably it is this that fails in the dreaming scenario, rather than(again) the paucity of our evidence (see entry onthe analysis of knowledge). Therefore, it can be held that there is an asymmetry between the goodcase and the skeptical scenario even if we grant that we have the sameevidence in both cases.

The Cartesian skeptic can nevertheless raise an uncomfortable questionat this point: what is this alleged evidence in favor of theproposition that we are not in a skeptical scenario? One temptinganswer is that the evidence in question consists precisely of thoseexternal world propositions which are the target of the Cartesianargument. I know that I have hands, and, according to this view, thatvery proposition is my evidence for the proposition that I am not ahandless brain in a vat. But recall our discussion of Dretske’smule case. There we pointed out that Dretske is, in effect,assimilating Closure and Transmission principles—i.e., assumingthat the only way in which Closure principles can hold is if someevidencee is evidence both forp and anyqentailed byp. We noted then that there is at least anotherpossibility: it might be that we must be antecedently justified inbelievingq in order to be justified in believing somepwhich entails it. And indeed, it seems plausible that this is thedirection of the evidential relation between external worldpropositions and the negation of skeptical hypotheses: we cannot bejustified in believing external world propositions unless we haveantecedent justification for believing the negation of skepticalhypotheses (but cf. Pryor 2000).

Another alternative is to say that no evidence justifies us inbelieving the negations of skeptical hypotheses, but that we arenevertheless justified in believing them. On one version of this view,put forward by Crispin Wright 2004, ourentitlement toaccept that we are not in a skeptical scenario does notdepend on our having any kind of evidence, either empirical orapriori (see also Coliva (2015) for a development of a view inthis neighborhood). Indeed, we are entitled to accept thosepropositions because unless we were we would not be justified inbelievingany proposition. Notice two importantterminological points in the statement of Wright’s view: hedoesn’t think that we are justified in believing that we are notin a skeptical scenario, but that we are entitled to accept thatproposition. What are the differences between justification andentitlement, on the one hand, and belief and acceptance, on the other?Roughly, what we are calling justification Wright calls“warrant”. He thinks that there are two kinds of warrant:we can be warranted in believing a proposition because we have anevidential justification for it (where the evidence consists of thepropositions we are warranted in believing or accepting), or we can beentitled to accept it even in the absence of any justification forthem. As for the difference between belief and acceptance, Wright isprepared to grant that to count as a belief an attitude must beevidence-based, and so entitlements cannot be entitlements to believe.To be entitled to accept a proposition, for Wright, is to be justifiedin behaving (where “behavior” is understood broadly, toinclude cognitive inferential behavior, for instance) approximately asone would if one believed the proposition.

On another version of the view, although we do not have empiricalevidence for the proposition that we are not in a skeptical scenario,we do have a kind of justification for it which does not restexclusively on the fact that if we didn’t then we wouldn’tbe justified in believing anything. Stewart Cohen 2010 has argued thatour justification for believing that we are not in a skepticalscenario derives from the rationality of certain inferential rules(see also Wedgwood 2013). One such rule justifies us in concluding(defeasibly) that there is something red in front of us if we have anexperience with the content that there is something red in front ofus. Now, we can use that rule “online”, when we do in facthave an experience with the content that there is something red infront of us, or “offline”, assuming for the sake ofargument that we have an experience with the content that there issomething red in front of us to see what follows from it. According tothe rule in question, it follows (again, defeasibly) that there issomething red in front of us. We can now cancel the assumption byconcluding (defeasibly) with the following conditional: if I have anexperience with the content that there is something red in front ofme, then there is something red in front of me. Notice that thisconditional is incompatible with one specific skeptical hypothesis:the hypothesis that (for whatever reason) I have an experience withthe content that there is something red in front of me but there isnothing red in front of me.

4. Contextualism

So far, we have looked at reasons for and against the two premises ofthe CP argument for Cartesian Skepticism. A different kind of approachto the argument requires some setup. Philosophers routinelydistinguish betweensentences and thepropositionsexpressed by some of them. Sentences are language-dependent entitieswhereas propositions are (something like) the informational content ofsome of those language-dependent entities (see entry onpropositions). Thus, we distinguish between the proposition that it is raining andthe English sentenceIt is raining. That very sameproposition can be expressed by other sentences, such as the SpanishsentenceEstá lloviendo. Moreover, which proposition agiven sentence expresses (if any) can depend on contextualfactors—that is to say, the same sentence may express oneproposition when produced in a given a context, and a different onewhen produced in a different context. Thus, when Tomás saysthat it is raining he expresses the proposition that it is raining inTucson on May 14, 2019, whereas when Manolo said “Estálloviendo” last week, he expressed the proposition that it wasraining in Mar del Plata on May 10, 2019.

The contextualist response to the argument for Cartesian Skepticismrests on the claim that which propositions the sentences used in thatargument express is also a context-sensitive matter. Differentcontextualists would fill in the details in different ways—herewe follow most closely the contextualism of Cohen 1987, 1988, 2000,2005, 2014a,b, but see also Lewis 1996, DeRose 1992, 1995, 2002, 2004,2005 and Stine 1976. Notice, to begin with, that justification comesin degrees: one can be more justified in believing one propositionthan another. But there is also such a thing as being justifiedtout court. In this respect, it can be argued that“justified” is like “tall”, in that we canmake sense both of comparative uses, such as when we say thatTomás is taller than his mother, and of non-comparative ones,such as when we say that Jordan is tall. Notice also that whichproposition is expressed by a non-comparative use of“tall” does not float free from what would be appropriatecomparative uses. Thus, when I say “Jordan is tall”, whatI say is true provided that Jordan is taller than the average subjectin the relevant contrast class. Thus, if Jordan is a fifth-grader,then what I said would be true if Jordan is taller than the averagefifth-grader, whereas if Jordan is an NBA player, then what I saidwould be true if Jordan is taller than the average NBA player (whoplays in Jordan’s position, perhaps). Similarly, thecontextualist claims that when I say that I am justified in believinga proposition, what I say is true if and only if my degree ofjustification for believing the proposition is higher than acontextually set threshold. That threshold, moreover, can vary withthe conversational context. Thus, if we are doing epistemology andthinking about the requirements for justification, the thresholdrequired for an utterance of “I am justified in believing I havehands” goes up to the point where few (if any) of us would countas having said something true, whereas in an everyday context thethreshold goes down to the point where most of us would count ashaving said something true.

According to contextualism, then, there is no single propositionexpressed by the sentences used in the CP-based argument for CartesianSkepticism. Rather, there are many such propositions. Two interestingones are the propositions expressed in everyday contexts, where CP2 aswell as the conclusion of the argument express false propositions, andthose expressed in heightened-scrutiny contexts, where both CP2 aswell as the conclusion of the argument express true propositions. CP1(as well as CP itself) always expresses a true proposition, as long aswe do not change contexts mid-sentence. Thus, the contextualistresponse to the CP-based argument is that it is at least twoarguments: a sound one, when produced in heightened-scrutiny contexts,and one with a false premise (and a false conclusion) when produced inordinary contexts. Contextualism is thus a more concessive response tothe skeptic than the ones we have canvassed so far, for it concedesthat the sentences used in the argument for Cartesian Skepticism canbe used to express propositions which constitute a sound argument.

But even though Contextualism represents a concessive answer toskepticism, it is certainly not concessive enough in the eyes of theskeptic. For the contextualist simply asserts that, in ordinarycontexts, we are justified in rejecting skeptical hypotheses. Butrecall that the skeptic’s idea was that CP2 is true even when wehave in mind even minimally demanding standards for justification. Inother words, the skeptic claims that we are not justified in believingthe negation of skeptical hypotheses even a little bit, not just thatwe do not meet a very stringent standard for justification. Now, theskeptic might well be wrong about this, but the contextualist, quacontextualist, does not have any argument for his trademark claim thatwe do have some justification for believing the negation of skepticalhypotheses. In this respect, contextualism as a response to theskeptic is parasitic on some independent argument to the effect thatwe do have that kind of justification.

A related issue regarding Contextualism pertains to its relevance toskepticism. Grant, if only for the sake of argument, thatContextualism regarding knowledge and justification attributions istrue. That is to say, grant that there are multiple properties that,say, “justified” could refer to. Couldn’t skeptics,and epistemologists more generally, be interested in a subset (perhapsjust one) of them? If so, the interesting epistemological argumentswould pertain to the conditions under which that property isinstantiated, and Contextualism would fall by the wayside. For adebate regarding this and related issues, see Conee 2014a,b and Cohen2014a,b.

A view which is related to, but crucially different from,Contextualism goes under various names in the literature:“Subject-Sensitive Invariantism”, “Interest RelativeInvariantism” or views which admit of “pragmaticencroachment” (see Fantl and McGrath 2002, 2007, 2009; Hawthorne2003; and Stanley 2005). Whereas the contextualist thinks that thesame sentence attributing justification can express differentpropositions depending on the context in which it is produced, thesubject-sensitive invariantist thinks that the proposition expressedis invariant, but its truth-value depends on features of the subjectwhich can vary (such as how important it is to the subject that thebelief in question be true). Very roughly, a version ofsubject-sensitive invariantism has it that a sentence of the form“S is justified in believingp” invariantlyexpresses a proposition which entails thatS’sjustification for believingp is at least high enough forS to be rational in acting as ifp is true. Notice thatwhether it is rational forS to act as ifp istraditionally thought to depend on two things: the degree ofjustificationS has for believing thatp (or, perhapsmore commonly in the context of decision theory, which degree ofbelief, or credence,S is justified in assigning top),andS’s preferences. Thus, the more sensitiveS’s preferences are with respect to whetherp istrue, the more justified in believingp S must be for theproposition thatS is justified (tout court) inbelievingp to be true. For instance, if nothing much hangs,forS, on whether there is orange juice in the house, a faintmemory of having seen some in the fridge might be enough for it to betrue thatS is justified in believing that there is orangejuice in the house. On the other hand, ifS is diabetic andneeds to ingest some sugar quickly, that same faint memory might notbe enough for that same proposition to be true. Notice the differencebetween Contextualism and Subject-Sensitive Invariantism: thecontextualist might say that the same sentence (thatS isjustified in believing that there is orange juice in the house)expresses two different propositions (one true, the other false)depending on whether the conversational context includes theinformation thatS is diabetic and needs to ingest sugar; thesubject-sensitive invariantist, on the other hand, holds that thesentence in question always expresses the same proposition, but thatvery proposition is true in the first case but false in thesecond.

Subject-Sensitive Invariantism has been subject to a number ofcriticisms (see McGrath 2004; DeRose 2002, 2004, 2005; Cohen 2005;Comesaña 2013; Anderson and Hawthorne, 2019a,b), but thegeneral approach has also been ably defended (see the previously citedwork by Fantl and McGrath). Nevertheless, the same issue that arosewith respect to Contextualism seems to arise here. TheSubject-Sensitive Invariantist needs an independent argument to theeffect that we can be justified at least to a minimal degree inbelieving the negations of skeptical hypotheses, for otherwise histrademark claim that propositions attributing us justification forbelieving such claims are true is itself unjustified.

5. Pyrrhonian Skepticism

We turn now to Pyrrhonian Skepticism.^[17] We remind the reader that our main interest here is not historical(for which see the entry onancient skepticism), but rather systematic: we want to canvass the legacy of PyrrhonianSkepticism for contemporary epistemology, and in so doing we set asideeven the most cursory exegetical interest.

Recall that, according to Pyrrhonian Skepticism, suspension ofjudgment is the only justified attitude with respect toanyproposition (yes, including the proposition that suspension ofjudgment is the only justified attitude with respect to anyproposition). We are interested here in whether there are goodarguments for such a view. We begin by recalling the tri-partitedistinction between belief, disbelief and suspension of judgment. Ifwe identify disbelief in a proposition with belief in its negation,then we are left with two attitudes within the realm of coarse-grainedepistemology: belief and suspension of judgment. We assume also thatthe arguments to follow are addressed to someone who has an interestin, and has considered, the propositions in question. Otherwise, thereis always the possibility of not taking any attitude whatsoevertowards a proposition. Such lack of an attitude cannot itself be(epistemically) justified or not. But if the subject is to take anattitude, then the argument for Pyrrhonian Skepticism has it thatsuspension of judgment is the only justified one.

The Pyrrhonian skeptics sought suspension of judgment as a way ofachieving calm (ataraxia) in the face of seeminglyintractable disagreement. The Pyrrhonians had a number of ways, or“modes”, to induce suspension of judgment. The importanceof Pyrrhonian Skepticism to contemporary epistemology derivesprimarily from these modes, and in particular from a subset of themreferred to collectively as “the modes of Agrippa”. Thereare five modes associated with Agrippa, but three of them are the mostimportant: the mode of hypothesis (or unsupported assertion), the modeof circularity (“reciprocal”), and the mode of regressionto infinity. The three modes of Agrippa function together in thefollowing way. Whenever the dogmatist (Sextus refers to those who arenot skeptics as “dogmatists”, and we will follow him inthis) asserts his belief in a proposition \(p_1\), the Pyrrhonian willchallenge that assertion, asking the dogmatist to justify \(p_1\), togive reasons for thinking that it is true. The dogmatist will theneither decline to answer the challenge or adduce another proposition\(p_2\) in support of \(p_1\). If the dogmatist refuses to answer thechallenge, the Pyrrhonian will be satisfied that the only justifiedattitude to take with respect to \(p_1\) is to suspend judgment,because no reason for it has been given (thus appealing to the mode ofhypothesis). If the dogmatist adduces another proposition \(p_2\) insupport of \(p_1\), then either \(p_2\) will be identical to \(p_1\)or it will be a different proposition. If \(p_2\) is the sameproposition as \(p_1\), then the Pyrrhonian will also suspend judgmentwith respect to \(p_1\), because no proposition can support itself(thus appealing to the mode of circularity). If, on the other hand,\(p_2\) is different from \(p_1\), then the Pyrrhonian will ask thedogmatist to justify his assertion of \(p_2\). And now either thedogmatist offers no reason in support of \(p_2\), or offers \(p_2\)itself or \(p_1\) as a reason, or adduces yet another proposition\(p_3\), different from both \(p_1\) and \(p_2\). If the dogmatistoffers no reason for \(p_2\), then the Pyrrhonian will invoke the modeof hypothesis again and suspend judgment in accordance with it; ifeither \(p_2\) itself or \(p_1\) are offered as reasons to believe in\(p_1\), then the Pyrrhonian will invoke the mode of circularity andsuspend judgment in accordance with it (because not only can noproposition be a reason for believing in itself, but also no genuinechain of reasons can loop); and, finally, if the dogmatist offers yetanother proposition \(p_3\), different from both \(p_1\) and \(p_2\),as a reason to believe \(p_2\), then the same three possibilities thatarose with respect to \(p_2\) will arise with respect to \(p_3\). Thedogmatist will not be able to continue offering different propositionsin response to the Pyrrhonian challenge forever—eventually,either no reason will be offered, or a proposition that has alreadymade an appearance will be mentioned again. The Pyrrhonian refers tothis impossibility of actually offering a different proposition eachtime a reason is needed as “the mode of infiniteregression”. The three Pyrrhonian modes, then, work in tandem inorder to induce suspension of judgment with respect to any propositionwhatsoever.

The Pyrrhonian use of the three modes of Agrippa in order to inducesuspension of judgment can be presented in the form of an argument,which has been called “Agrippa’s trilemma”. It is atleast somewhat misleading to present the Pyrrhonian position in termsof an argument, because when someone presents an argument they areusually committed to the truth of its premises and its conclusion,whereas Pyrrhonian skeptics would suspend judgment with respect tothem. Nevertheless, presenting an argument for Pyrrhonian Skepticismdoesn’t do much violence to this skeptical position, becausewhat is important is not whether the Pyrrhonians themselves accept thepremises or the validity of the argument, but rather whetherwe do. If we do, then it seems that we ourselves should bePyrrhonian skeptics (and if we do become Pyrrhonian skeptics as aresult of this argument, we can then start worrying about what to dowith respect to the fact that an argument whose premises webelieved—and perhaps still believe—to be true convinced usthat we are not justified in believing anything). If we do not thinkthat the argument is sound, then we stand to learn somethinginteresting about the structure of an epistemologicaltheory—because each of the premises of the apparently validargument looks plausible at first sight.

Before presenting a reconstruction of Agrippa’s trilemma we needto introduce some definitions. Let’s say that a belief isinferentially justified if and only if it is justified (atleast in part) in virtue of its relations to other beliefs. Ajustified basic belief, by contrast, is a belief that isjustified but not in virtue of its relations to other beliefs. Aninferential chain is a set of beliefs such that every memberof the set is allegedly related to at least one other member by therelation “is justified by”. Agrippa’s trilemma,then, can be presented thus:

Premise 1 is beyond reproach, given our previous definitions. Premise2 is justified by the mode of hypothesis. Step 3 of the argumentfollows from premises 1 and 2. Premise 4 is also beyondreproach—the only remaining possible structure for aninferential chain to have is to contain basic justified beliefs, butthere are none of those according to premise 2. Premise 5 is justifiedby appeal to the mode of infinite regression, and premise 6 isjustified by appeal to the mode of circularity. Premise 7 might seemto be a truism, but we will have to take a closer look at it.

It is interesting to note that Agrippa’s trilemma is perfectlygeneral; in particular, it applies to philosophical positions as wellas to ordinary propositions. In fact, when Agrippa’s trilemma isapplied to epistemological theories themselves, the result is what hasbeen called “the problem of the criterion” (see Chisholm1973).

Many contemporary epistemological positions can be stated as areaction to Agrippa’s trilemma. In fact, all of premises 2, 5, 6and 7 have been rejected by different philosophers at one time oranother. We examine those responses in what follows.

5.1 Rejecting Premise 2: Foundationalism

Foundationalists claim that there are basic justifiedbeliefs—beliefs that are justified but not in virtue of theirrelations to other beliefs. In fact, according to foundationalism, alljustified beliefs are either basic beliefs or are justified (at leastin part) in virtue of being inferentially related to a justifiedbelief (or to some justified beliefs). This is where foundationalismgets its name: the edifice of justified beliefs has its foundation inbasic beliefs.

But how do foundationalists respond to the mode of hypothesis? If abelief is not justified by another belief, then isn’t it just ablind assertion? If basic beliefs are justified but not by otherbeliefs, thenhow are they justified? What else besidesbeliefs is there that can justify beliefs?

To this last question, many foundationalists reply: experience (we aretalking here about empirical knowledge;a priori knowledgeraises interesting problems of its own, and it is of course alsosubject to Agrippa’s trilemma). To a rough first approximationthat glosses over many important philosophical issues, experiences aremental states that, like beliefs, aim to represent the world as it is,and, like beliefs too, can fail in achieving that aim—that is,experiences can misrepresent. Nevertheless, experiences are not to beidentified with beliefs, for it is possible to have an experience asof, e.g., facing two lines that differ in length without having thebelief that one is facing two lines that differ in length—acombination of mental states that anyone familiar with theMüller-Lyer illusion will recognize.

There are three important questions that any foundationalist has toanswer. First, what kinds of beliefs do experiences justify? Second,how must inferentially acquired beliefs be related to basic beliefs inorder for them to be justified? Third, in virtue of what doexperiences justify beliefs?

With respect to the first question, we can distinguish betweentraditional foundationalism and moderate foundationalism. Traditionalfoundationalists think that basic beliefs are beliefsaboutexperiences, whereas moderate foundationalists think that experiencecan justify beliefs about the external world. Take, for example, theexperience that you typically have when looking at a tomato under goodperceptual conditions—an experience that, remember, can be hadeven if no tomato is actually there.^[18] A moderate foundationalist would say that that experience justifiesyou in believing that there is a tomato in front of you. Thetraditional foundationalist, on the other hand, would say that theexperience justifies you only in believing that you have an experienceas of a tomato in front of you. You may well be justified in believingthat there is a tomato in front of you, but only inferentially.

A traditional argument in favor of traditional foundationalism relieson the fact that whereas you can be mistaken regarding whether thereis a tomato in front of you when you have an experience as of facing atomato, you cannot, in the same situation, be mistaken regardingwhether you are undergoing such an experience. From the point of viewof traditional foundationalism, this fact indicates that the moderatefoundationalist is taking an unnecessary epistemic risk—the riskof having a foundation composed of false beliefs.

The moderate foundationalist can reply that the traditionalfoundationalist must undertake a similar risk. For, while it is truethat if one is undergoing a certain experience then one cannot bemistaken in thinking that one is undergoing that experience, one canstill be mistaken about one’s experiences—for instance,perhaps one can believe that one is in pain even if the experiencethat one is undergoing is actually one of feeling acutelyuncomfortable. And if it were just as difficult to distinguish betweenthe true and the false in the realm of beliefs about our ownexperiences as it is in the realm of beliefs about the external world,then we could be wrong about which of our own beliefs are basicallyjustified and which are not. If this kind of meta-fallibilism isaccepted, then why not accept the further kind according to whichbasic justified beliefs can be false? Of course, the resolution ofthis dispute depends on whether, as the moderate believes, we can bemistaken about our own experiences.

What about our second question: how must basic beliefs be related toinferentially justified beliefs? Here too there are two differentkinds of foundationalism: deductivism and non-deductivism. Accordingto the deductivist, the only way in which a (possibly one-membered)set of basic justified beliefs can justify another belief is bylogically entailing that other belief. In other words, therehas to be avalid argument at least some of whose premisesare basic justified beliefs^[19] and whose conclusion is the inferentially justified belief inquestion. Given that the argument is valid, the truth of the premisesguarantees the truth of the conclusion—it is impossible for allthe premises to be true while the conclusion is false. Non-deductivismallows relations other than logical entailment as possiblejustificatory relations. For instance, many foundationalists willclaim that goodinductive inferences from basic justifiedbeliefs provide their conclusions with justification—even thoughinductive arguments are not valid, that is, even though it is possiblefor all the premises of a good inductive argument to be true while itsconclusion is false. Although these are independent distinctions,traditional foundationalists tend to be deductivists, whereas moderatefoundationalists tend to be non-deductivists. Notice that for atraditional, deductivist foundationalist, there cannot be falsejustified beliefs. Many contemporary epistemologists would shy awayfrom this strong form of infallibilism, and take that consequence tobe an argument against the conjunction of traditional foundationalismand deductivism.

The question that is most interesting from the point of view ofPyrrhonian Skepticism is our third one: what is it about the relationbetween an experience and a belief that, according to thefoundationalist, allows the former to justify the latter? (Analogousquestions apply to non-foundationalist positions too, and thediscussion to follow is not restricted to the specific case offoundationalism.) There are three different proposals about how toanswer this question that are the most prominent. Let’s call theprinciples that assert that a subject is justified in having a certainbelief given that she is undergoing a certain experience,“epistemic principles”. Our third question can then bestated as follows: what makes epistemic principles true?

The first proposal, which we shall call “primitivism”,claims that the question cannot have an intelligible answer. There isno more basic fact in virtue of which epistemic principles obtain.They describe bedrock facts, not to be explained in terms of anythingelse, but are instead to be used to explain other facts.Epistemological theorizing, according to the primitivist, ends withthe discovery of the correct epistemic principles (for views alongthese lines, see Chisholm 1966 [and also the second and thirdeditions: 1977, 1989] and Feldman & Conee 1985).

The other two positions are non-primitivist.Internalistnon-primitivism holds that epistemic principles are true in virtue offacts about ourselves—for instance, one prominent internalistview is that which epistemic principles are true for a given subjectis determined by which epistemic principles that subject would acceptunder deep reflection (see Foley 1993).^[20]Externalist non-primitivism holds that epistemic principlesare true in virtue of facts that are not about ourselves—forinstance, one prominent externalist view is that certain experiencesprovide justification for certain beliefs because the obtaining ofthose experiences is reliably connected to the truth of those beliefs(that is, it couldn’t easily happen that those experiencesobtain without those beliefs being true; see Goldman 1979).

Both externalists and internalists think that primitivists areoverlooking real facts, whereas primitivists think that there arefewer things in heaven and earth than are dreamt of in non-primitivistphilosophy. Within the non-primitivist camp, externalists think thatinternalists have too subjective a conception of epistemology—tosome extent, thinking it so, or being disposed to think it so underconditions of deep reflection, makes it so for the internalist.Internalists, for their part, are likely to think that externalistsare no longer engaged in the same project that both skeptics andinternalist epistemologists are engaged in, the project of determining“from the inside” whether one’s beliefs arejustified or amount to knowledge, because the obtaining of a relationbetween a belief of his and the external world is something that thesubject is in no position to ascertain “from theinside”.

5.2 Rejecting Premise 5: Infinitism

Infinitism, the claim that infinite evidential chains can providejustification to their members, is the answer to Agrippa’strilemma that has received the least attention in the literature. Thisis due, at least in part, to the fact that infinitism has to deal withwhat might seem like formidable obstacles. For instance, it seems thatno one actually has an infinite number of beliefs. To this objection,the infinitist is likely to reply that actually occurring beliefs arenot needed, only implicit beliefs that are available to the subject inorder to continue constructing his inferential chain if called upon todo so (by others or by himself). The plausibility of this replydepends on whether good sense can be made of the notion of implicitbelief and the notion of an implicit belief’s being availablefor a subject. A second apparently formidable problem for infinitismhas to do with the fact that the mere appeal to a new belief,regardless of its epistemic status, cannot provide justification tothe belief we started out with. In other words, infinitism seems torun afoul of the following principle:

The infinitist might reply that he does not run afoul of thatprinciple, because the beliefs adduced in support of the initialbeliefs are themselves justified by beliefs further down the chain.But what goes for the initial set of beliefs goes, it seems, forlonger chains. If the appeal to a single unjustified belief cannot doany justificatory work of its own, why would appealing to a largenumber of unjustified beliefs do any better? Even leaving that problemaside, the infinitist, like the coherentist, maintains thatjustification can arise merely in virtue of relations among beliefs.Infinitists will then have to respond to many of the same objectionsthat are leveled against coherentism—in particular, they wouldhave to respond to the isolation objection mentioned in the nextsection. (See Aikin 2011 and Klein 1999, 2007 for defenses ofinfinitism; and see Turri & Klein 2014; Aikin & Peijnenburg2014; and Peijnenburg & Wenmackers 2014 for collections of essayswhich defend or criticize various forms of infinitism.)

5.3 Rejecting Premise 3: Coherentism

Coherentists reject two related features of the picture of evidentialreasons that underlies Agrippa’s trilemma. The first feature isthe idea that justification is anasymmetrical relation: if abelief \(p_1\) justifies a different belief \(p_2\), then \(p_2\) doesnot justify \(p_1\). The second feature is the idea that the unit ofjustification is the individual belief. Putting these two rejectionstogether, the coherentist believes that justification is a symmetricaland holistic matter. It is not individual beliefs that are justifiedin the primary sense of the word, but only complete systems ofbeliefs—individual beliefs are justified, when they are, invirtue of belonging to a justified system of beliefs. The centralcoherentist notion of justification is best taken to be a comparativeone: a system of beliefs B1 is better justified than a system ofbeliefs B2 if and only if B1 has a greater degree of internalcoherence than B2. One crucial question that coherentists have toanswer, of course, is what it takes for one system of beliefs to havea greater degree of coherence than another. Many coherentists havethought that explanatory relations will be crucial in elucidating thenotion of coherence: the more explanatorily integrated a system is,the more coherence it displays (see Quine & Ullian 1970 [1978] andBonJour 1978).

The main objection that coherentists have to answer has been called“the isolation objection”. The objection centers on thefact that, according to the coherentist, the justification of a systemof beliefs is entirely a matter of relations among the beliefsconstituting the system. But this runs against the strong intuitionthat experience has a very important role to play in the justificationof beliefs. To illustrate the problem, suppose that you and I bothhave a highly coherent set of beliefs—your system, it is safe toassume, contains the belief that you are reading, whereas minedoesn’t, and it contains instead the belief that I am swimming(because, let us suppose, I am swimming right now). Suppose now thatwe switch systems of beliefs—somehow, you come to have my set ofbeliefs and I come to have yours. Given that coherence is entirely amatter of relations among beliefs, your system will be as coherent inmy mind as it was in yours, and vice-versa. And yet, our beliefs arenow completely unjustified—there you are, reading, believingthat you are swimming, and here I am, swimming, believing that I amreading. In other words, certain transformations that preservecoherence in a system of beliefs do not seem to preservejustification.

In reply, coherentists have argued that it is possible to giveexperience a role without sacrificing the idea that coherence isentirely a matter of relations among beliefs—one idea is torequire that any minimally acceptable system of beliefs containbeliefs about the experiences that the subject is undergoing (seeBonJour 1985 and Lehrer 1990). It is fair to say that there is noagreement regarding whether this move can solve the problem.

5.4 Rejecting Premise 7: Positism

One position that can be traced back to some ideas inWittgenstein’sOn Certainty (Wittgenstein1969)—and, perhaps, also to Ortega’sIdeas yCreencias (Ortega y Gasset 1940)—is that evidential chainshave to terminate in beliefs that are not properly said to be eitherjustified or unjustified. This position, which we shall call“Positism” (not to be confused with“positivism”), shares many features with Foundationalism:for instance, both positists and foundationalists agree thatinferential chains have to be finite and non-circular. But, whereasthe foundationalist thinks that the starting points of inferentialchains are beliefs that are justified by something other than beliefs,the positist thinks that the starting points of inferential chains arebeliefs that are not justified by anything—they are posits thatwe have to believe without justification. Despite this differencebetween the positist and the foundationalist, the positions arestructurally similar enough that analogues of the questions posed tothe foundationalist can be asked of the positist.^[21]

First, then, which beliefs are such that they are not justified andyet are the starting points of every inferential chain—in otherwords, how do we identify which are the posits? One answer that can begleamed from Wittgenstein’sOn Certainty, which we willcall “relativistic Positism”, is that this is a matterthat is relative both to time and society, because what the posits areis determined by some function of the actual positing practices of themembers of one’s society at a certain time. Thus, according toWittgenstein, the proposition that no one has been to the moon was aposit for a certain long period of time—it was a propositionthat no one felt the need to justify, and that was presupposed in manyjustificatory practices. For obvious reasons, though, that propositioncan no longer appropriately function as a posit. Otherepistemologists, “non-relativistic positists”, think thatwhich beliefs are properly posited depends on some objective truthabout which beliefs have to be presupposed in order to engage in thepractice of justifying beliefs at all. One prime candidate for playingthis role is the first-person belief that I am not being deceived byan evil demon into thinking that I am a normally embodied and situatedhuman being (this is the view advocated by Wright 2004 that we alreadyalluded to in section 3.2).

The second question, regarding how posits must be related to inferredbeliefs in order to justify them, can receive answers that arecompletely analogous to the foundationalists’.

The third question, applied to positism, is the question why certainbeliefs are properly posited. Relativistic positists answer that thisis so because of a certain societal fact: because they are taken to beso by an appropriate sub-sector of a certain society at a certaintime. Non-relativistic positists answer that a certain belief isproperly taken as a posit just in case every justificatory act that weengage in presupposes that the belief in question is true.

One objection that positists of both sorts have to face is that theyare transforming a doxastic necessity into an epistemicvirtue—that is, they are concluding that certain beliefs canproperly serve as the starting points of inferential chains becausethat is how in fact they are treated (relativistic Positism) orbecause otherwise it wouldn’t be possible to engage ininferential practices at all (non-relativistic Positism). ThePyrrhonian skeptic, of course, will reply that the mere fact that mostmembers of a society accept a certain belief without justification, oreven the fact that if we don’t do so then we cannot justifyanything else, doesn’t mean that it should be accepted withoutjustification.

5.5 Rejecting More than One Premise

Perhaps the most interesting recent development in relation toPyrrhonian Skepticism is that more and more epistemologists arearguing that the proper way to reply to Agrippa’s trilemma is tocombine some of the positions that, for ease of exposition, we havepresented as mutually exclusive. Thus, for example, many contemporaryepistemologists put forward theories that contain elements of bothFoundationalism and Coherentism (see, for instance, Haack 1993). It isa testament to the endurance of Pyrrhonian Skepticism thatphilosophers continue in this way to grapple with it.

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Descartes, René: epistemology |epistemic closure |justification, epistemic: coherentist theories of |justification, epistemic: foundationalist theories of |justification, epistemic: internalist vs. externalist conceptions of |perception: the disjunctive theory of |skepticism: ancient |transmission of justification and warrant

Acknowledgments

Thanks to an anonymous referee for helpful suggestions.