## 1. Knowledge, Justification and Skepticism



Philosophically interesting forms of skepticism claim that we do not
know propositions which we ordinarily think we do know. We should
distinguish such skepticism from the ordinary kind, the claim that we
do 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 know
that there are an even number of stars in the Milky Way, but it is a
form of philosophical skepticism to say that we do not know that the
sun will come out tomorrow. Even though our interest is in
philosophical skepticism, we can start our inquiry by thinking about
ordinary skepticism.



Why do we readily grant, then, that we don't know that there are
an even number of stars in the Milky Way? To begin with, the vast
majority of us do not even believe that proposition, and it is widely
acknowledged that knowledge requires
 belief.[1]
 But even those who believe it do not know it, even if they luck out
and it is true. They do not know it because they are not
*justified* in believing it, and knowledge requires
 justification.[2]
 Of course, they are not justified in disbelieving that proposition
either. Belief and disbelief are two of the so-called *doxastic
attitudes* that we can adopt towards a proposition. We can also,
of course, not even consider a proposition, and thus not adopt any
doxastic attitude towards it. But most philosophers would hold that in
addition to belief and disbelief there is a third possible doxastic
attitude that we can adopt towards a proposition: we can *suspend
judgment* (or withhold assent) with respect to it. Suspension of
judgment is thus a *bona fide* doxastic attitude alongside
belief and disbelief, and is not to be equated with the failure to
adopt 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 any
doxastic attitude) can itself be justified or unjustified. For
instance, we would ordinarily think that suspension of judgment is
*not* justified with respect to the proposition that Paris is
the Capital of France, but it is with respect to the proposition that
there 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 argue
that we do not know certain propositions because our beliefs in them
are not *sensitive* (in a sense to be explained below), and
they claim that sensitivity is a condition on knowledge--but
perhaps not on justified belief. We will examine the bearing of the
sensitivity condition on skeptical arguments assuming that it applies
to justification. But even if an argument for philosophical skepticism
targets our knowledge in a certain area while remaining silent about
whether we have justified beliefs in that area, that argument will
still indirectly target our justification as well. For, if the
argument succeeds, then it provides us with knowledge (or at least
justified belief) that we do not know a certain proposition *p*.
And it is plausible to hold that if we know (or justifiably believe)
that we do not know a proposition *p*, then we are not even
justified in believing *p*.



In what follows, then, we identify skepticism with respect to a field
of propositions *F* as the claim that the only justified attitude
with respect to propositions in *F* is suspension of judgment.
Philosophical skepticism, then, differs from ordinary skepticism at
least regarding the field of propositions to which it is claimed to
apply. But even within the realm of philosophical skepticism we can
make an interesting distinction by appealing to the scope of the
thesis.


## 2. Two Basic Forms of Philosophical Skepticism



One interesting distinction between kinds of philosophical skepticism
pertains to the question whether they iterate. Thus, consider
skepticism about the future: the claim that the only justified
attitude with respect to propositions about the future is suspension
of judgment. That kind of philosophical skepticism overlaps partly
with ordinary skepticism about the future. We should all grant, for
instance, that we should suspend judgment with respect to the
proposition that the flip of this fair coin in the next second will
come up heads, but most of us think that we should believe, not
suspend judgment with respect to, the proposition that the sun will
come out tomorrow. Being a skeptic with respect to the first-order
proposition that the sun will come out tomorrow (that is to say,
holding that the only justified attitude with respect to that
proposition is suspension of judgment) can be combined with any of the
three doxastic attitudes with respect to the second-order proposition
that the only justified attitude with respect to the proposition that
the sun will come out tomorrow is to suspend judgment. Generalizing,
whenever the skeptic holds that the only justified attitude with
respect to a field of propositions *F* is to suspend judgment, we
can ask them which attitude is justified with respect to the
proposition that the only justified attitude with respect to any
proposition in *F* is suspension of judgment. Perhaps the most
straightforward answer here is that the only justified attitude with
respect to that second-order proposition is belief. After all,
isn't skepticism with respect to *F* *precisely* the
belief that we should suspend judgment with respect to any proposition
in *F*? We will call this combination of views--the view
that we should suspend judgment with respect to any proposition in
*F* and believe the proposition that we should suspend judgment
with respect to any proposition in *F*--"Cartesian
Skepticism", because of the skeptical arguments investigated by
Descartes and his critics in the mid-seventeenth century. Other
philosophers, following an ancient tradition, refer to this view as
"Academic Skepticism" (see the entry on
 ancient skepticism).



But some skeptics are skeptics regarding second- (and higher-) order
propositions as well as regarding first-order propositions. Following
the same ancient tradition, we will call that kind of skepticism
"Pyrrhonian Skepticism". Without any claim to historical
accuracy, we will take Pyrrhonian Skepticism to be absolute
skepticism--the thesis that suspension of judgment is the only
justified attitude with respect to *any* proposition *p*.
Is Pyrrhonian Skepticism so understood self-refuting? It is certainly
formally consistent: no contradiction follows just from the
propositions that the only justified attitude with respect to the
proposition that *p* is suspension of judgment and that the only
justified attitude with respect to the proposition that the only
justified attitude with respect to the proposition that *p* is
suspension of judgment is suspension of judgment (say that three times
fast!). But consider the principle that whenever someone is committed
to a proposition *p* they are also (perhaps implicitly) committed
to the proposition that belief is the (or at least a) justified
attitude towards *p*. Call this the "Commitment Iteration
Principle". If the Commitment Iteration Principle holds, then
Pyrrhonian Skepticism is indeed self-refuting. For Pyrrhonian skeptics
are committed to the claim that suspension of judgment is the only
justified attitude with respect to some proposition *p*. By the
Commitment Iteration Principle, they are then committed to the claim
that belief is a justified attitude with respect to the proposition
that suspension of judgment is the only justified attitude with
respect to *p*. Therefore, if they are in addition committed to
the claim that suspension of judgment is the only justified attitude
with respect to that very same proposition, they are committed to an
inconsistent set of propositions. But Pyrrhonian skeptics need not
hold the Commitment Iteration Principle. Indeed, they are committed to
thinking that suspension of judgment is the only justified attitude
with respect to the Commitment Iteration Principle itself (and also
with respect to analogous principles which may make trouble for
Pyrrhonian Skepticism). Of course, Pyrrhonian Skepticism will not be
acceptable to anyone who does hold the Commitment Iteration
Principle--but neither will Pyrrhonian Skepticism be acceptable
to anyone who holds that we should not suspend judgment with respect
to some proposition. It is not clear, then, that the charge of
self-refutation represents an independent indictment of Pyrrhonian
Skepticism. In any case, contemporary philosophers find Pyrrhonian
Skepticism interesting not because they take seriously the possibility
of its truth, but rather because there are interesting arguments in
its favor, the responses to which shape the contours of many
contemporary epistemological theories.



We have distinguished between Cartesian and Pyrrhonian Skepticism, but
we have characterized both views in terms of a generic field of
propositions *F*. In the case of Pyrrhonian Skepticism, *F*
includes every proposition, but we can generate different versions of
Cartesian Skepticism by varying *F*. A prominent version of
Cartesian 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 Cartesian
Skepticism and Pyrrhonian Skepticism.


## 3. The Argument for Cartesian Skepticism Employing the Closure Principle



Many contemporary philosophers take the canonical argument for
Cartesian Skepticism to involve skeptical hypotheses and a Closure
Principle
 (CP).[5]
 A skeptical hypothesis (with respect to a proposition *p* and a
subject *S*) is a proposition *SH* such that if *SH*
were true, then: (a) *S* would not know *p*, and (b)
*S* would not be able to distinguish *SH* from a situation
where *S* knows *p*. The evil demon scenario that Descartes
envisions at the end of his "First Meditation" functions
as a near-universal skeptical hypothesis, for the demon has the power
to deceive any subject regarding almost any proposition. One way in
which a *SH* may satisfy (a) is by describing a situation where
*p* is false, but this is not the only way. Descartes' evil
demon may induce in a disembodied subject's mind an experience
as of the subject's own hands in front of her, as a result of
which the subject believes that there are hands in front of her, while
at the same time dangling some unattached hands in front of the
subject (we are waiving here difficulties having to do with how to
locate objects relative to disembodied subjects). The subject's
belief that there are hands in front of her is in that case true, but
she still doesn't know it. The connection between Closure
principles and arguments for skepticism gets complicated if we
countenance skeptical hypotheses which do not entail the falsehood of
the proposition in question, and so in what follows we limit our
discussion to those that do.



Letting "*h*" stand for any proposition about the
external world we would ordinarily take ourselves to be justified in
believing, for example, G. E. Moore's famous "here's
a hand" (Moore 1939 [1993]), and re-using "*SH*" for a
skeptical hypothesis relative to *h* (we leave the subject
tacit), we can state the contemporary canonical *CP-style argument
for Cartesian Skepticism* as follows:



* CP1. If I am justified in believing that *h*, then I am
justified in believing that \({\sim}\textit{SH}\).
* CP2. I am not justified in believing that
\({\sim}\textit{SH}\).
* Therefore, I am not justified in believing that *h*.




CP1 follows from the following Closure Principle (letting
"*Jx*" stand for *the subject is justified in
believing *x**):




**Closure Principle** [**CP**]: For all
propositions *x* and *y*, if *x* entails *y*, and
*Jx*, then *Jy*.




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



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




**CP\*:** For all propositions, *x* and *y*, if
*x* entails *y*, and *Jx* to degree *u*, then
*Jy* to degree *v* (where \(u \le v)\).




There appear to be only three ways that one can respond to the
CP-style skeptical argument: deny at least one premise, deny that the
argument is valid, or reluctantly accept the conclusion--if
neither 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 for
some properties, for example, truth. If *p* is true and implies
*q*, then *q* is true. It just as clearly does not hold for
other properties, for example being surprising. It might be surprising
that Tomas is taller than his father, but it is certainly not
surprising that Tomas is taller than someone, and yet the
former entails the latter. What about justified belief? Does Closure
hold for it?



It might be thought that the answer must be a clear "No",
for the following reasons. First, notice that every logical truth is
entailed by every proposition. If Closure held for justification, then
we would have to say that everybody is justified in believing every
logical truth (provided that we are willing to grant that everybody is
justified in believing at least one proposition). But this
doesn't seem plausible. Some logical truths are too complicated
to even parse, let alone be justified in believing. If this is true,
then Closure doesn't hold for belief (that is to say, we may
fail to believe propositions entailed by propositions we already
believe). The existence of very complicated logical truths also
underlies another worry for Closure. For to every logical entailment
between propositions there corresponds a logical truth: the (material)
conditional with the entailing proposition in the antecedent and the
entailed proposition in the consequent. Some of these logically true
conditionals will be examples of propositions that we are not
justified in believing (if only because the consequent is too
complicated for beings like us to even parse). In that case, we might
well be justified in believing their antecedents without being
justified 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 CP
includes only contingent propositions that are within *S*'s
capacity to grasp and (ii) that the entailment is
"obvious" to *S*. The skeptic can agree to those
restrictions because the skeptical scenarios are posited in such a way
as to render it obvious that our ordinary beliefs are false in those
scenarios, and it is taken to be a contingent claim that *S* is
in the actual circumstances as described in the antecedent. (For a
full discussion of the required repairs of CP, see David &
Warfield 2008 and Hawthorne 2014.)



There is one other important, required clarification of the restricted
version of CP. "Justified belief" is ambiguous. It could
be used to refer to a species of actually held beliefs--namely,
those actually held beliefs of *S* that are justified. Or it
could refer to propositions that *S* is justified in
believing--regardless of whether *S* does indeed believe
them. Following Roderick Firth, the distinction between actually held
justified beliefs and propositions one is justified in believing,
regardless of whether they are actually believed, is often marked by
distinguishing between doxastic and propositional justification (see
Firth 1978). If CP is to be acceptable, "justified in
believing" in the consequent must be used so as to refer to
propositional justification for a reason already cited, i.e., that
Closure does not hold for belief. In other words, one of
*S*'s actual beliefs, *p*, might be justified and
*S* still fail to believe some proposition that is entailed by
 *p*.[6]



We are now in a position to ask: Does the restricted form of closure
hold? There are at least three types of argument against closure in
the literature: alleged counterexamples, alleged unpalatable
consequences, and incompatibility with allegedly plausible
epistemological theories. In the remainder of this section we examine
one exemplar of each of these.



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



> 
> 
> ...something's being a zebra implies that it is not a
> mule...cleverly disguised by the zoo authorities to look like a
> zebra. Do you know that these animals are not mules cleverly
> disguised? If you are tempted to say "Yes" to this
> question, think a moment about what reasons you have, what evidence
> you can produce in favor of this claim. The evidence you *had*
> for thinking them zebras has been effectively neutralized, since it
> does not count toward their *not* being mules cleverly
> disguised to look like zebras. (Dretske 1970: 1015-1016)
> 
> 
> 



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



The crucial thing to note about this proposed counterexample is that
it works only if the Closure Principle entails that the very same
source of evidence that justifies *S* in believing that the
animals are zebras must justify *S* in believing that they are
not cleverly disguised mules. Since the evidence for the former has
been "effectively neutralized", it is not available for
the latter. Now, in response one could claim that once the question of
whether the animals are disguised mules has been raised, the evidence
is "effectively neutralized" for both the former and the
latter, and *S* is no longer justified in believing that the
animals are zebras. Thus, it could be held that this example could
actually be used to support CP. Nevertheless, let us grant that the
evidence for the claim that the animals are zebras cannot be used to
show that they are not cleverly disguised mules. Still, it could be
argued that this would not force giving up CP.



Such an argument could begin by recalling that CP claimed merely that
whenever a subject is justified in believing *p*, then that
subject is justified in believing *q*. CP does not require that
the subject have the same evidence for *p* as she does for
*q*. Dretske's purported counterexample seems to require
that CP implies that the adequate source of evidence is the same for
both propositions.



No doubt this constraint sometimes correctly portrays the relevant
evidential relationships when some proposition entails some other
proposition. For example, suppose I have adequate evidence for the
claim that Anne has two brothers. Then it would seem that the very
same evidence would be adequate for believing that Anne has at least
one brother. But the defender of CP, and more particularly the
Cartesian Skeptic, could point out that closure does not require this
to hold for every case.



There are two other possibilities. First, one may hold that when
*p* entails *q* and there is some evidence *e* for
*p*, it is *p* itself that is evidence for *q*. For
example, it may be held that given that I have adequate evidence for
believing that 2 is a prime number, I can use that very proposition
(that 2 is a prime number) as an adequate reason for believing that
there is at least one even prime. (See Klein 1981, 1995, and 2000, but
see below for reasons for doubting that this is a genuine
possibility.) Second, there are cases where the order is reversed
because *q* serves as part of the evidence for *p*. For
example, suppose that I am justified, *ceteris paribus*, in
believing that (pure) water is present if I am justified in believing
that there is present, at standard temperature and pressure, a clear,
odorless, watery-tasting and watery-looking fluid that contains
hydrogen and oxygen. This pattern is typical of abductive inferences,
and is often referred to as "inference to the best
explanation". (See Vogel 1990, 2014b for a discussion of Cartesian Skepticism and inference to
the best explanation.) In addition, there are cases in which it seems
that some contraries of *h* need to be eliminated prior to
*h*'s being justified. For example, reconsidering the
zebra-in-the-zoo case, it seems to be true that if I had some good
reason to think that the animals are cleverly disguised mules, such a
contrary would need to be eliminated before I would be justified in
believing that the animals were
 zebras.[8]



It could also be argued that CP has unacceptable consequences. Of
course, one of those unacceptable consequences may well be Cartesian
Skepticism itself, but to point that out in the present context would
be dialectically unhelpful. It has been argued, however, that CP by
itself has far-reaching skeptical consequences. Notice that the
argument for Cartesian Skepticism under consideration contains CP2 as
an essential premise. The present concern is that CP by itself (and
therefore CP1, if justified on the basis of CP), without help from
CP2, has skeptical consequences. If that were true, that would be a
reason to be wary of CP, for it would be a much stronger principle
than advertised.



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




**Ampliativity**: It is possible for a subject *S*
to be justified in believing *h* on the basis of evidence
*e* even if *S* does not have independent justification (of
at least the same degree of *S*'s justification for
believing *h*) for believing a proposition *p* such that
*p* and *e* together entail *h*.




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



The next principle is in conflict with what we presented above as an
alternative possibility to Dretske's interpretation of the
evidential structure of CP. Dretske's counterexample works, we
said, only if CP holds that whatever justifies the subject in
believing *p* is also what justifies her in believing *q*.
But there are two other possibilities. Maybe the evidential relation
is reversed: whatever justifies us in believing *q* justifies us
in believing *p*. Or maybe, we said, *p* itself, and not
whatever justifies us in believing *p*, justifies us in believing
*q*. The next principle goes directly against this
possibility:




**Mere Lemmas**: If *S* is justified in believing
*p* on the basis of some evidence *e*, then *p* itself
can justify *S* in believing some other proposition *q* only
if *e* justifies *S* in believing *q*.




We call the principle "Mere Lemmas" because the idea
behind it is that if a proposition is a mere lemma, in the sense that
it derives all of its justification from some prior evidence *e*,
then it doesn't have justificatory powers of its own,
independent of the justificatory powers of *e*. Suppose, for
instance, that you start out by knowing that Jim has a pet, but you
don't know what kind of pet it is (the example is from Pryor
2004). Then you come to know that it is a hairless pet. Now you become
justified (perhaps to a small degree) in believing that Jim's
pet is a hairless dog. That is to say, whatever degree of
justification you had before to believe that Jim's pet is a
hairless dog, you are now somewhat more justified in believing that
same proposition. That Jim's pet is a hairless dog of course
entails that Jim's pet is a dog. But your justification for
believing that Jim's pet is a hairless dog cannot in any way be
transmuted into justification for believing that Jim's pet is a
dog. Whatever degree of justification you had before for believing
that Jim's pet is a dog, you are now less justified in believing
that same proposition (because hairless dogs are a small minority of
hairless pets).



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



Our final principle is the following:




**Entailment**: If *p* entails *q*, then
*q* cannot justify *S* in disbelieving *p*.




The idea behind this principle is that if *p* entails *q*,
then should *q* turn out to be true then things are as *p*
says they are, and so we can hardly use *q* as evidence against
*p*. We return to Entailment below, but first we show how these
three principles are in conflict with CP.



Assume, with Ampliativity, that a subject *S* is justified in
believing a proposition *h* on the basis of some evidence
*e* without having independent justification for believing any
other proposition *p* such that *p* together with *e*
entails *h*. Notice that *h* obviously entails *h or
not-e*. Therefore, by CP, *S* is justified in believing *h
or not-e*. But, of course, *e* together with *h or
not-e* entails *h*. Therefore, if *S* is justified in
believing *h* on the basis of *e*, then there is a
proposition which *S* is justified in believing and which
together with *e* entails *h*.



Notice that this is close to, but not quite, the negation of
Ampliativity. For Ampliativity denies that there will be any such
proposition which *S* is *independently* justified in
believing, and for all we have said *S*'s justification for
believing *h or not-e* is not independent. Independent of what?
Of *S*'s justification for believing *h* itself. For
all we have said so far, *S* might be justified in believing
*h or not-e* on the basis of *h*, or on the basis of
*e* itself.



But, given Mere Lemmas, *h* cannot justify *S* in believing
any proposition unless *e* does. Therefore, the only option left
open, short of denying Ampliativity, is to argue that *e* itself
justifies *S* in believing *h or not-e*. But that is
incompatible with Entailment. For notice that for *e* to justify
*S* in believing *h or not-e* is for *e* to justify
*S* in disbelieving its negation, i.e., *e and not-h*.
But, of course, *e and not-h* entails *e*, and so the
entailment principle has it that *e* cannot justify *S* in
disbelieving *e and not-h*--i.e., *e* cannot justify
*S* in believing *h or not-e*.



Although this particular reconstruction is our own (for more on it,
see Comesana forthcoming), some philosophers have taken
arguments similar to it to count against CP (see, for example, Huemer
2001 and Sharon & Spectre 2017, and cf. Comesana 2017).
However, others have argued against Entailment (see, for example,
Pryor 2014a,b and Vogel 2014b), and yet others have argued that denying Ampliativity
itself is not as absurd as it might sound (Comesana 2014a,b).
The argument cannot, therefore, be taken to be a conclusive blow
against 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 that *p* *iff*:


1. *S* believes *p*;
2. *p* is true;
3. if *p* were true, *S* would believe *p*;
4. if *p* were not true, *S* would not believe
*p*.



Nozick called his account a "tracking" account of
knowledge because whenever *S* knows that \(p, S\)'s
beliefs track *p*. Think of a guided missile *tracking*
its target. If the target were to move left, the missile would move
left. If the target were not to move left, the missile would not move
left. According to the tracking account of knowledge our beliefs must
track the truth if we are to have knowledge.



There is one important clarification of conditions 3 and 4 that is
discussed by Nozick, namely, that the method by which *S*
acquires the belief must be held constant from the actual world to the
possible world. A doting grandmother might know that her grandchild is
not a thief on the basis of sufficiently good evidence, but would
still believe that he wasn't a thief, even if he were, because
she loves him. So, we must require that the grandmother use the same
method 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's
account of
 knowledge.[11]
 What is crucial for our discussion is that it is easy to see that, if
Nozick's account is correct, closure will fail for knowledge in
just the kind of case that the Cartesian Skeptic is putting forward
because of condition (4). Suppose *S* knows that there is a chair
before her. Would she know that she is not in a skeptical scenario in
which it merely appears that there is a chair? If the fourth condition
were a necessary condition of knowledge, she would not know that
because if she were in such a scenario, she would be fooled into
thinking that she wasn't. Thus, either condition (4) is too
strong 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 glass
of ice-cold lemonade on a picnic table in your backyard. You go inside
and get a telephone call from a friend and talk for half an hour. When
you hang up you remember that you had left the ice-cold lemonade
outside exposed to the hot sun and come to believe that it isn't
ice-cold anymore. It would seem that you could know that. Indeed, if
it were false, that could only be due to some bizarre circumstance.
Thus, if the lemonade were still ice-cold, you would believe that it
wasn't (see Vogel 1987: 206). The moral of this (and similar)
cases seems to be that sensitivity is not a correct condition on
knowledge.



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


### 3.2 Consideration of CP2



CP2 claims that we are not justified in denying the skeptical
hypothesis--in other words, that we are not justified in
believing that we are not being deceived. What arguments can be given
for CP2? It is tempting to suggest something like this: The skeptical
scenarios are developed in such a way that it is assumed that we
*could not* tell that we were being deceived. For example, we
are asked to consider that there is an Evil Genius "so
powerful" that it could (1) make me believe that there were
hands when there were none and (2) make it such that I *could*
not detect the illusion. But the skeptic must be very careful here.
She cannot require that in order for *S* to know (or be justified
in believing) something, say *x*, that if *x* were false,
she would not still believe *x*. We have just seen (while
examining Nozick's account of knowledge) that this requirement
is arguably too strong. So the mere fact that there could be skeptical
scenarios in which *S* still believes that she is not in such a
scenario cannot provide the skeptic with a basis for thinking that she
fails to know that she is not (actually) in a skeptical scenario. But
even more importantly, were that a requirement of knowledge (or
justification), then we have seen that closure would fail and,
consequently, the basis for the first premise in the CP-style argument
for Cartesian Skepticism would be
 forfeited.[12]




Ernest Sosa has argued for three interrelated theses regarding CP2 and
Nozick's sensitivity condition: (i) that sensitivity can be
easily confused with a different condition on knowledge (which Sosa
calls safety); (ii) that while sensitivity is not a correct necessary
condition on knowledge, safety is; (iii) finally, that our belief in
the negation of skeptical hypotheses is safe despite being
 insensitive.[13]



Nozick's sensitivity condition is a *subjunctive
conditional*: if *p* were false, *S* would not believe
it. The usual way in which such conditionals are evaluated is by
assuming that there is an ordering of *possible worlds*
according to how much they resemble the actual world. A subjunctive
conditional \(A \rightarrow B\) is true if and only if *B* is
true in the closest (or all the closest) possible worlds where
*A* is true. According to this semantics, subjunctive
conditionals do not contrapose (the contrapositive of a conditional
*if A, B* is *if not-B, not-A*). Thus, suppose that we
flip a coin to decide whether you or I will strike this match: heads
you strike it, tails I do. The coin comes up head, you strike the
match and it lights. In this situation, it is true that if I had
struck the match, it would have lit. But it doesn't seem to be
true that if the match hadn't lit then I wouldn't have
struck it. The match might have failed to lit because it was wet while
either of us struck it. In the possible worlds terminology, the
closest possible world where I strike the match is a world where it
lights, but there are possible worlds where the match doesn't
light and I strike it that are as close to actuality as are worlds
where the match doesn't light and you strike it.



After noticing the failure of subjunctives to contrapose, Sosa
proposed that we should replace Nozick's sensitivity condition
with its contrapositive, which Sosa calls a 'safety'
condition. The following formulation seems to capture Sosa's
intent:




**Safety**: *S*'s belief that *p* based
on *e* is safe if and only if *S* would not easily believe
that *p* based on *e* without it being so that *p* (in
symbols, *S believes that p on basis* \(e \rightarrow p\)).
(Sosa
 2002)[14]




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



Sosa's idea, then, is that we can explain away the temptation to
think that CP2 is true by noticing that although safety and
sensitivity are easily confused with one another, my belief that I am
not the victim of a skeptical scenario is insensitive but safe, and
that whereas sensitivity is not a condition on knowledge, safety
is.



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



> 
> 
> **Halloween Party**: There is a Halloween party at
> Andy's house, and I am invited. Andy's house is very
> difficult to find, so he hires Judy to stand at a crossroads and
> direct people towards the house (Judy's job is to tell people
> that 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 tells
> Judy that if she sees Michael she should tell him the same thing she
> tells everybody else (that the party is at the house down the left
> road), but she should immediately phone Andy so that the party can be
> moved to Adam's house, which is down the right road. I seriously
> consider disguising myself as Michael, but at the last moment I
> don't. When I get to the crossroads, I ask Judy where the party
> is, and she tells me that it is down the left road.
> 
> 
> 



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



So far, we have argued that there are dangers in defending CP2 by
appealing to the sensitivity condition, and that Sosa's attack
on CP2 might itself be subject to doubt. What else can be said for or
against CP2?



Let's go back to the rough idea that there is some kind of
epistemic symmetry between what we take to be the actual case and a
skeptical scenario. Of course, if we were the victims in a skeptical
scenario, we wouldn't know that we are not (if only because it
would be false, but perhaps not only because of that). Given symmetry,
even if we are not victims of a skeptical scenario, we do not know
that we are not. Moreover, we know all of this. As we suggested in
section 1, if we know that we don't know that *p*, then we
are not even justified in believing that *p*. Therefore, CP2.
Every step in this argument can be challenged, but there is no doubt
that many philosophers find something along these lines at least worth
thinking about. Let us take a closer look at the first step, the claim
that there is an epistemic symmetry between the good case and the
skeptical scenario.



What can this alleged symmetry amount to? One idea is that we have the
same evidence in both cases. According to a Cartesian account of this
common evidence, it consists in mental states of the subject, such as
her experiences. By construction, the subject has the same experiences
in the skeptical scenario as she does in the good case. But some
philosophers, most notably Williamson 2000, have denied that we have
the same evidence in the good and the skeptical case. According to
Williamson, our evidence is constituted not by our experiences, but by
what we know. Given that in the good case we know more propositions
that in the bad case, we have more evidence in the good case than we
do in the skeptical case. In the good case, for instance, we know
mundane propositions such as the proposition that we have hands. Given
that knowledge entails justification, in the good case we are
justified in believing that we have hands. Given CP, in the good case
we are justified in believing that we are not in the skeptical case.
This account of evidence entails that the relation of
indiscriminability between the good case and the skeptical case is not
symmetric: victims of a skeptical scenario cannot distinguish the
skeptical scenario from the good case (for all they know, they are in
the good case, and for all they know, they are in the skeptical case),
but subjects in the good case can distinguish between the cases (they
know that they are in the good case, and--again, given
CP--they know that they are not in the skeptical
 case).[16]



But even those contemporary philosophers who grant that our epistemic
position with respect to external world propositions is the same in
the normal case as in the skeptical scenario can object to the
symmetry thesis. For even granting (as we must) that in the skeptical
scenario we do not know that we are not in the skeptical scenario, it
doesn't follow that in the ordinary case we do not know that we
are not in the skeptical scenario, not even assuming that we have the
same evidence in both cases. To begin with, an obvious difference
between the normal case and the skeptical scenario is that in the
skeptical scenario the proposition in question (that we are not in the
skeptical scenario) is false, whereas in the normal case it is true.
Given that knowledge requires truth, we can explain why we lack
knowledge in the skeptical scenario by appealing to this truth
condition on knowledge, rather than to the paucity of our evidence. In
other words, our evidence for thinking that we are not in the
skeptical scenario, this reply holds, is good enough to know that
proposition, if only it were true. Now, the skeptic can then reply
that not all skeptical scenarios are such that external worlds
propositions are false in them. For instance, if I am right now
dreaming 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 the
introduction of skeptical hypotheses which do not entail the falsity
of external world propositions complicates the CP argument, but let us
here bracket that issue. For, in addition to truth, knowledge
plausibly requires other non-evidential conditions. In the wake of the
Gettier problem, for instance, many philosophers have accepted that
besides belief, justification and truth, the right kind of relation
between the truth of the proposition and the belief must hold, and
arguably it is this that fails in the dreaming scenario, rather than
(again) the paucity of our evidence (see entry on
 the analysis of knowledge).
 Therefore, it can be held that there is an asymmetry between the good
case and the skeptical scenario even if we grant that we have the same
evidence in both cases.



The Cartesian skeptic can nevertheless raise an uncomfortable question
at this point: what is this alleged evidence in favor of the
proposition that we are not in a skeptical scenario? One tempting
answer is that the evidence in question consists precisely of those
external world propositions which are the target of the Cartesian
argument. I know that I have hands, and, according to this view, that
very proposition is my evidence for the proposition that I am not a
handless brain in a vat. But recall our discussion of Dretske's
mule case. There we pointed out that Dretske is, in effect,
assimilating Closure and Transmission principles--i.e., assuming
that the only way in which Closure principles can hold is if some
evidence *e* is evidence both for *p* and any *q*
entailed by *p*. We noted then that there is at least another
possibility: it might be that we must be antecedently justified in
believing *q* in order to be justified in believing some *p*
which entails it. And indeed, it seems plausible that this is the
direction of the evidential relation between external world
propositions and the negation of skeptical hypotheses: we cannot be
justified in believing external world propositions unless we have
antecedent justification for believing the negation of skeptical
hypotheses (but cf. Pryor 2000).



Another alternative is to say that no evidence justifies us in
believing the negations of skeptical hypotheses, but that we are
nevertheless justified in believing them. On one version of this view,
put forward by Crispin Wright 2004, our *entitlement* to
*accept* that we are not in a skeptical scenario does not
depend on our having any kind of evidence, either empirical or *a
priori* (see also Coliva (2015) for a development of a view in
this neighborhood). Indeed, we are entitled to accept those
propositions because unless we were we would not be justified in
believing *any* proposition. Notice two important
terminological points in the statement of Wright's view: he
doesn't think that we are justified in believing that we are not
in a skeptical scenario, but that we are entitled to accept that
proposition. What are the differences between justification and
entitlement, 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 an
evidential justification for it (where the evidence consists of the
propositions we are warranted in believing or accepting), or we can be
entitled to accept it even in the absence of any justification for
them. As for the difference between belief and acceptance, Wright is
prepared to grant that to count as a belief an attitude must be
evidence-based, and so entitlements cannot be entitlements to believe.
To be entitled to accept a proposition, for Wright, is to be justified
in behaving (where "behavior" is understood broadly, to
include cognitive inferential behavior, for instance) approximately as
one would if one believed the proposition.



On another version of the view, although we do not have empirical
evidence for the proposition that we are not in a skeptical scenario,
we do have a kind of justification for it which does not rest
exclusively on the fact that if we didn't then we wouldn't
be justified in believing anything. Stewart Cohen 2010 has argued that
our justification for believing that we are not in a skeptical
scenario 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 an
experience with the content that there is something red in front of
us. Now, we can use that rule "online", when we do in fact
have an experience with the content that there is something red in
front of us, or "offline", assuming for the sake of
argument that we have an experience with the content that there is
something red in front of us to see what follows from it. According to
the rule in question, it follows (again, defeasibly) that there is
something red in front of us. We can now cancel the assumption by
concluding (defeasibly) with the following conditional: if I have an
experience with the content that there is something red in front of
me, then there is something red in front of me. Notice that this
conditional is incompatible with one specific skeptical hypothesis:
the hypothesis that (for whatever reason) I have an experience with
the content that there is something red in front of me but there is
nothing red in front of me.


## 4. Contextualism



So far, we have looked at reasons for and against the two premises of
the CP argument for Cartesian Skepticism. A different kind of approach
to the argument requires some setup. Philosophers routinely
distinguish between *sentences* and the *propositions*
expressed by some of them. Sentences are language-dependent entities
whereas propositions are (something like) the informational content of
some of those language-dependent entities (see entry on
 propositions).
 Thus, we distinguish between the proposition that it is raining and
the English sentence *It is raining*. That very same
proposition can be expressed by other sentences, such as the Spanish
sentence *Esta lloviendo*. Moreover, which proposition a
given sentence expresses (if any) can depend on contextual
factors--that is to say, the same sentence may express one
proposition when produced in a given a context, and a different one
when produced in a different context. Thus, when Tomas says
that it is raining he expresses the proposition that it is raining in
Tucson on May 14, 2019, whereas when Manolo said "Esta
lloviendo" last week, he expressed the proposition that it was
raining in Mar del Plata on May 10, 2019.



The contextualist response to the argument for Cartesian Skepticism
rests on the claim that which propositions the sentences used in that
argument express is also a context-sensitive matter. Different
contextualists would fill in the details in different ways--here
we 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 comes
in degrees: one can be more justified in believing one proposition
than another. But there is also such a thing as being justified
*tout court*. In this respect, it can be argued that
"justified" is like "tall", in that we can
make sense both of comparative uses, such as when we say that
Tomas is taller than his mother, and of non-comparative ones,
such as when we say that Jordan is tall. Notice also that which
proposition is expressed by a non-comparative use of
"tall" does not float free from what would be appropriate
comparative uses. Thus, when I say "Jordan is tall", what
I say is true provided that Jordan is taller than the average subject
in the relevant contrast class. Thus, if Jordan is a fifth-grader,
then what I said would be true if Jordan is taller than the average
fifth-grader, whereas if Jordan is an NBA player, then what I said
would be true if Jordan is taller than the average NBA player (who
plays in Jordan's position, perhaps). Similarly, the
contextualist claims that when I say that I am justified in believing
a proposition, what I say is true if and only if my degree of
justification for believing the proposition is higher than a
contextually set threshold. That threshold, moreover, can vary with
the conversational context. Thus, if we are doing epistemology and
thinking about the requirements for justification, the threshold
required for an utterance of "I am justified in believing I have
hands" goes up to the point where few (if any) of us would count
as having said something true, whereas in an everyday context the
threshold goes down to the point where most of us would count as
having said something true.



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



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



A related issue regarding Contextualism pertains to its relevance to
skepticism. Grant, if only for the sake of argument, that
Contextualism regarding knowledge and justification attributions is
true. 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 (perhaps
just one) of them? If so, the interesting epistemological arguments
would pertain to the conditions under which that property is
instantiated, and Contextualism would fall by the wayside. For a
debate regarding this and related issues, see Conee 2014a,b and Cohen
2014a,b.



A view which is related to, but crucially different from,
Contextualism goes under various names in the literature:
"Subject-Sensitive Invariantism", "Interest Relative
Invariantism" or views which admit of "pragmatic
encroachment" (see Fantl and McGrath 2002, 2007, 2009; Hawthorne
2003; and Stanley 2005). Whereas the contextualist thinks that the
same sentence attributing justification can express different
propositions depending on the context in which it is produced, the
subject-sensitive invariantist thinks that the proposition expressed
is invariant, but its truth-value depends on features of the subject
which can vary (such as how important it is to the subject that the
belief in question be true). Very roughly, a version of
subject-sensitive invariantism has it that a sentence of the form
"*S* is justified in believing *p*" invariantly
expresses a proposition which entails that *S*'s
justification for believing *p* is at least high enough for
*S* to be rational in acting as if *p* is true. Notice that
whether it is rational for *S* to act as if *p* is
traditionally thought to depend on two things: the degree of
justification *S* has for believing that *p* (or, perhaps
more commonly in the context of decision theory, which degree of
belief, or credence, *S* is justified in assigning to *p*),
and *S*'s preferences. Thus, the more sensitive
*S*'s preferences are with respect to whether *p* is
true, the more justified in believing *p S* must be for the
proposition that *S* is justified (*tout court*) in
believing *p* to be true. For instance, if nothing much hangs,
for *S*, on whether there is orange juice in the house, a faint
memory of having seen some in the fridge might be enough for it to be
true that *S* is justified in believing that there is orange
juice in the house. On the other hand, if *S* is diabetic and
needs to ingest some sugar quickly, that same faint memory might not
be enough for that same proposition to be true. Notice the difference
between Contextualism and Subject-Sensitive Invariantism: the
contextualist might say that the same sentence (that *S* is
justified 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 the
information that *S* is diabetic and needs to ingest sugar; the
subject-sensitive invariantist, on the other hand, holds that the
sentence in question always expresses the same proposition, but that
very proposition is true in the first case but false in the
second.



Subject-Sensitive Invariantism has been subject to a number of
criticisms (see McGrath 2004; DeRose 2002, 2004, 2005; Cohen 2005;
Comesana 2013; Anderson and Hawthorne, 2019a,b), but the
general approach has also been ably defended (see the previously cited
work by Fantl and McGrath). Nevertheless, the same issue that arose
with respect to Contextualism seems to arise here. The
Subject-Sensitive Invariantist needs an independent argument to the
effect that we can be justified at least to a minimal degree in
believing the negations of skeptical hypotheses, for otherwise his
trademark claim that propositions attributing us justification for
believing 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 on
 ancient skepticism),
 but rather systematic: we want to canvass the legacy of Pyrrhonian
Skepticism for contemporary epistemology, and in so doing we set aside
even the most cursory exegetical interest.



Recall that, according to Pyrrhonian Skepticism, suspension of
judgment is the only justified attitude with respect to *any*
proposition (yes, including the proposition that suspension of
judgment is the only justified attitude with respect to any
proposition). We are interested here in whether there are good
arguments for such a view. We begin by recalling the tri-partite
distinction between belief, disbelief and suspension of judgment. If
we identify disbelief in a proposition with belief in its negation,
then we are left with two attitudes within the realm of coarse-grained
epistemology: belief and suspension of judgment. We assume also that
the arguments to follow are addressed to someone who has an interest
in, and has considered, the propositions in question. Otherwise, there
is always the possibility of not taking any attitude whatsoever
towards a proposition. Such lack of an attitude cannot itself be
(epistemically) justified or not. But if the subject is to take an
attitude, then the argument for Pyrrhonian Skepticism has it that
suspension of judgment is the only justified one.



The Pyrrhonian skeptics sought suspension of judgment as a way of
achieving calm (*ataraxia*) in the face of seemingly
intractable disagreement. The Pyrrhonians had a number of ways, or
"modes", to induce suspension of judgment. The importance
of Pyrrhonian Skepticism to contemporary epistemology derives
primarily from these modes, and in particular from a subset of them
referred to collectively as "the modes of Agrippa". There
are five modes associated with Agrippa, but three of them are the most
important: the mode of hypothesis (or unsupported assertion), the mode
of circularity ("reciprocal"), and the mode of regression
to infinity. The three modes of Agrippa function together in the
following way. Whenever the dogmatist (Sextus refers to those who are
not skeptics as "dogmatists", and we will follow him in
this) asserts his belief in a proposition \(p\_1\), the Pyrrhonian will
challenge that assertion, asking the dogmatist to justify \(p\_1\), to
give reasons for thinking that it is true. The dogmatist will then
either decline to answer the challenge or adduce another proposition
\(p\_2\) in support of \(p\_1\). If the dogmatist refuses to answer the
challenge, the Pyrrhonian will be satisfied that the only justified
attitude to take with respect to \(p\_1\) is to suspend judgment,
because no reason for it has been given (thus appealing to the mode of
hypothesis). If the dogmatist adduces another proposition \(p\_2\) in
support 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 same
proposition as \(p\_1\), then the Pyrrhonian will also suspend judgment
with 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 the
dogmatist to justify his assertion of \(p\_2\). And now either the
dogmatist 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 dogmatist
offers no reason for \(p\_2\), then the Pyrrhonian will invoke the mode
of hypothesis again and suspend judgment in accordance with it; if
either \(p\_2\) itself or \(p\_1\) are offered as reasons to believe in
\(p\_1\), then the Pyrrhonian will invoke the mode of circularity and
suspend judgment in accordance with it (because not only can no
proposition be a reason for believing in itself, but also no genuine
chain of reasons can loop); and, finally, if the dogmatist offers yet
another proposition \(p\_3\), different from both \(p\_1\) and \(p\_2\),
as a reason to believe \(p\_2\), then the same three possibilities that
arose with respect to \(p\_2\) will arise with respect to \(p\_3\). The
dogmatist will not be able to continue offering different propositions
in response to the Pyrrhonian challenge forever--eventually,
either no reason will be offered, or a proposition that has already
made an appearance will be mentioned again. The Pyrrhonian refers to
this impossibility of actually offering a different proposition each
time a reason is needed as "the mode of infinite
regression". The three Pyrrhonian modes, then, work in tandem in
order to induce suspension of judgment with respect to any proposition
whatsoever.



The Pyrrhonian use of the three modes of Agrippa in order to induce
suspension of judgment can be presented in the form of an argument,
which has been called "Agrippa's trilemma". It is at
least somewhat misleading to present the Pyrrhonian position in terms
of an argument, because when someone presents an argument they are
usually committed to the truth of its premises and its conclusion,
whereas Pyrrhonian skeptics would suspend judgment with respect to
them. Nevertheless, presenting an argument for Pyrrhonian Skepticism
doesn't do much violence to this skeptical position, because
what is important is not whether the Pyrrhonians themselves accept the
premises or the validity of the argument, but rather whether
*we* do. If we do, then it seems that we ourselves should be
Pyrrhonian skeptics (and if we do become Pyrrhonian skeptics as a
result of this argument, we can then start worrying about what to do
with respect to the fact that an argument whose premises we
believed--and perhaps still believe--to be true convinced us
that we are not justified in believing anything). If we do not think
that the argument is sound, then we stand to learn something
interesting about the structure of an epistemological
theory--because each of the premises of the apparently valid
argument looks plausible at first sight.



Before presenting a reconstruction of Agrippa's trilemma we need
to introduce some definitions. Let's say that a belief is
*inferentially justified* if and only if it is justified (at
least in part) in virtue of its relations to other beliefs. A
*justified basic belief*, by contrast, is a belief that is
justified but not in virtue of its relations to other beliefs. An
*inferential chain* is a set of beliefs such that every member
of the set is allegedly related to at least one other member by the
relation "is justified by". Agrippa's trilemma,
then, can be presented thus:



1. If a belief is justified, then it is either a basic justified
belief or an inferentially justified belief.
2. There are no basic justified beliefs.



Therefore,


3. If a belief is justified, then it is justified in virtue of
belonging to an inferential chain.
4. All inferential chains are such that either (a) they contain an
infinite number of beliefs; or (b) they contain circles; or (c) they
contain beliefs that are not justified.
5. No belief is justified in virtue of belonging to an infinite
inferential chain.
6. No belief is justified in virtue of belonging to a circular
inferential chain.
7. No belief is justified in virtue of belonging to an inferential
chain that contains unjustified beliefs.



Therefore,


8. There are no justified beliefs.




Premise 1 is beyond reproach, given our previous definitions. Premise
2 is justified by the mode of hypothesis. Step 3 of the argument
follows from premises 1 and 2. Premise 4 is also beyond
reproach--the only remaining possible structure for an
inferential chain to have is to contain basic justified beliefs, but
there are none of those according to premise 2. Premise 5 is justified
by appeal to the mode of infinite regression, and premise 6 is
justified by appeal to the mode of circularity. Premise 7 might seem
to be a truism, but we will have to take a closer look at it.



It is interesting to note that Agrippa's trilemma is perfectly
general; in particular, it applies to philosophical positions as well
as to ordinary propositions. In fact, when Agrippa's trilemma is
applied to epistemological theories themselves, the result is what has
been called "the problem of the criterion" (see Chisholm
1973).



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


### 5.1 Rejecting Premise 2: Foundationalism



Foundationalists claim that there are basic justified
beliefs--beliefs that are justified but not in virtue of their
relations to other beliefs. In fact, according to foundationalism, all
justified beliefs are either basic beliefs or are justified (at least
in part) in virtue of being inferentially related to a justified
belief (or to some justified beliefs). This is where foundationalism
gets its name: the edifice of justified beliefs has its foundation in
basic beliefs.



But how do foundationalists respond to the mode of hypothesis? If a
belief is not justified by another belief, then isn't it just a
blind assertion? If basic beliefs are justified but not by other
beliefs, then *how* are they justified? What else besides
beliefs is there that can justify beliefs?



To this last question, many foundationalists reply: experience (we are
talking here about empirical knowledge; *a priori* knowledge
raises interesting problems of its own, and it is of course also
subject to Agrippa's trilemma). To a rough first approximation
that glosses over many important philosophical issues, experiences are
mental 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 be
identified with beliefs, for it is possible to have an experience as
of, e.g., facing two lines that differ in length without having the
belief that one is facing two lines that differ in length--a
combination of mental states that anyone familiar with the
Muller-Lyer illusion will recognize.



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



With respect to the first question, we can distinguish between
traditional foundationalism and moderate foundationalism. Traditional
foundationalists think that basic beliefs are beliefs *about*
experiences, whereas moderate foundationalists think that experience
can justify beliefs about the external world. Take, for example, the
experience that you typically have when looking at a tomato under good
perceptual conditions--an experience that, remember, can be had
even if no tomato is actually
 there.[18]
 A moderate foundationalist would say that that experience justifies
you in believing that there is a tomato in front of you. The
traditional foundationalist, on the other hand, would say that the
experience justifies you only in believing that you have an experience
as of a tomato in front of you. You may well be justified in believing
that there is a tomato in front of you, but only inferentially.



A traditional argument in favor of traditional foundationalism relies
on the fact that whereas you can be mistaken regarding whether there
is a tomato in front of you when you have an experience as of facing a
tomato, you cannot, in the same situation, be mistaken regarding
whether you are undergoing such an experience. From the point of view
of traditional foundationalism, this fact indicates that the moderate
foundationalist is taking an unnecessary epistemic risk--the risk
of having a foundation composed of false beliefs.



The moderate foundationalist can reply that the traditional
foundationalist must undertake a similar risk. For, while it is true
that if one is undergoing a certain experience then one cannot be
mistaken in thinking that one is undergoing that experience, one can
still be mistaken about one's experiences--for instance,
perhaps one can believe that one is in pain even if the experience
that one is undergoing is actually one of feeling acutely
uncomfortable. And if it were just as difficult to distinguish between
the true and the false in the realm of beliefs about our own
experiences as it is in the realm of beliefs about the external world,
then we could be wrong about which of our own beliefs are basically
justified and which are not. If this kind of meta-fallibilism is
accepted, then why not accept the further kind according to which
basic justified beliefs can be false? Of course, the resolution of
this dispute depends on whether, as the moderate believes, we can be
mistaken about our own experiences.



What about our second question: how must basic beliefs be related to
inferentially justified beliefs? Here too there are two different
kinds of foundationalism: deductivism and non-deductivism. According
to the deductivist, the only way in which a (possibly one-membered)
set of basic justified beliefs can justify another belief is by
*logically entailing* that other belief. In other words, there
has to be a *valid argument* at least some of whose premises
are basic justified
 beliefs[19]
 and whose conclusion is the inferentially justified belief in
question. Given that the argument is valid, the truth of the premises
guarantees the truth of the conclusion--it is impossible for all
the premises to be true while the conclusion is false. Non-deductivism
allows relations other than logical entailment as possible
justificatory relations. For instance, many foundationalists will
claim that good *inductive* inferences from basic justified
beliefs provide their conclusions with justification--even though
inductive arguments are not valid, that is, even though it is possible
for all the premises of a good inductive argument to be true while its
conclusion is false. Although these are independent distinctions,
traditional foundationalists tend to be deductivists, whereas moderate
foundationalists tend to be non-deductivists. Notice that for a
traditional, deductivist foundationalist, there cannot be false
justified beliefs. Many contemporary epistemologists would shy away
from this strong form of infallibilism, and take that consequence to
be an argument against the conjunction of traditional foundationalism
and deductivism.



The question that is most interesting from the point of view of
Pyrrhonian Skepticism is our third one: what is it about the relation
between an experience and a belief that, according to the
foundationalist, allows the former to justify the latter? (Analogous
questions apply to non-foundationalist positions too, and the
discussion to follow is not restricted to the specific case of
foundationalism.) There are three different proposals about how to
answer this question that are the most prominent. Let's call the
principles that assert that a subject is justified in having a certain
belief given that she is undergoing a certain experience,
"epistemic principles". Our third question can then be
stated 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 is
no more basic fact in virtue of which epistemic principles obtain.
They describe bedrock facts, not to be explained in terms of anything
else, but are instead to be used to explain other facts.
Epistemological theorizing, according to the primitivist, ends with
the discovery of the correct epistemic principles (for views along
these lines, see Chisholm 1966 [and also the second and third
editions: 1977, 1989] and Feldman & Conee 1985).



The other two positions are non-primitivist. *Internalist*
non-primitivism holds that epistemic principles are true in virtue of
facts about ourselves--for instance, one prominent internalist
view is that which epistemic principles are true for a given subject
is determined by which epistemic principles that subject would accept
under deep reflection (see Foley
 1993).[20]
*Externalist* non-primitivism holds that epistemic principles
are true in virtue of facts that are not about ourselves--for
instance, one prominent externalist view is that certain experiences
provide justification for certain beliefs because the obtaining of
those experiences is reliably connected to the truth of those beliefs
(that is, it couldn't easily happen that those experiences
obtain without those beliefs being true; see Goldman 1979).



Both externalists and internalists think that primitivists are
overlooking real facts, whereas primitivists think that there are
fewer things in heaven and earth than are dreamt of in non-primitivist
philosophy. Within the non-primitivist camp, externalists think that
internalists have too subjective a conception of epistemology--to
some extent, thinking it so, or being disposed to think it so under
conditions of deep reflection, makes it so for the internalist.
Internalists, for their part, are likely to think that externalists
are no longer engaged in the same project that both skeptics and
internalist epistemologists are engaged in, the project of determining
"from the inside" whether one's beliefs are
justified or amount to knowledge, because the obtaining of a relation
between a belief of his and the external world is something that the
subject is in no position to ascertain "from the
inside".


### 5.2 Rejecting Premise 5: Infinitism



Infinitism, the claim that infinite evidential chains can provide
justification to their members, is the answer to Agrippa's
trilemma that has received the least attention in the literature. This
is due, at least in part, to the fact that infinitism has to deal with
what might seem like formidable obstacles. For instance, it seems that
no one actually has an infinite number of beliefs. To this objection,
the infinitist is likely to reply that actually occurring beliefs are
not needed, only implicit beliefs that are available to the subject in
order to continue constructing his inferential chain if called upon to
do so (by others or by himself). The plausibility of this reply
depends on whether good sense can be made of the notion of implicit
belief and the notion of an implicit belief's being available
for a subject. A second apparently formidable problem for infinitism
has to do with the fact that the mere appeal to a new belief,
regardless of its epistemic status, cannot provide justification to
the belief we started out with. In other words, infinitism seems to
run afoul of the following principle:




**Principle of inferential justification**: If *S*
is justified in believing *p* on the basis of *S*'s
belief that *q*, then *S* is justified in believing
*q*.




The infinitist might reply that he does not run afoul of that
principle, because the beliefs adduced in support of the initial
beliefs are themselves justified by beliefs further down the chain.
But what goes for the initial set of beliefs goes, it seems, for
longer chains. If the appeal to a single unjustified belief cannot do
any justificatory work of its own, why would appealing to a large
number of unjustified beliefs do any better? Even leaving that problem
aside, the infinitist, like the coherentist, maintains that
justification can arise merely in virtue of relations among beliefs.
Infinitists will then have to respond to many of the same objections
that are leveled against coherentism--in particular, they would
have to respond to the isolation objection mentioned in the next
section. (See Aikin 2011 and Klein 1999, 2007 for defenses of
infinitism; and see Turri & Klein 2014; Aikin & Peijnenburg
2014; and Peijnenburg & Wenmackers 2014 for collections of essays
which defend or criticize various forms of infinitism.)


### 5.3 Rejecting Premise 3: Coherentism



Coherentists reject two related features of the picture of evidential
reasons that underlies Agrippa's trilemma. The first feature is
the idea that justification is an *asymmetrical* relation: if a
belief \(p\_1\) justifies a different belief \(p\_2\), then \(p\_2\) does
not justify \(p\_1\). The second feature is the idea that the unit of
justification is the individual belief. Putting these two rejections
together, the coherentist believes that justification is a symmetrical
and holistic matter. It is not individual beliefs that are justified
in the primary sense of the word, but only complete systems of
beliefs--individual beliefs are justified, when they are, in
virtue of belonging to a justified system of beliefs. The central
coherentist notion of justification is best taken to be a comparative
one: a system of beliefs B1 is better justified than a system of
beliefs B2 if and only if B1 has a greater degree of internal
coherence than B2. One crucial question that coherentists have to
answer, of course, is what it takes for one system of beliefs to have
a greater degree of coherence than another. Many coherentists have
thought that explanatory relations will be crucial in elucidating the
notion of coherence: the more explanatorily integrated a system is,
the more coherence it displays (see Quine & Ullian 1970 [1978] and
BonJour 1978).



The main objection that coherentists have to answer has been called
"the isolation objection". The objection centers on the
fact that, according to the coherentist, the justification of a system
of beliefs is entirely a matter of relations among the beliefs
constituting the system. But this runs against the strong intuition
that experience has a very important role to play in the justification
of beliefs. To illustrate the problem, suppose that you and I both
have a highly coherent set of beliefs--your system, it is safe to
assume, contains the belief that you are reading, whereas mine
doesn't, and it contains instead the belief that I am swimming
(because, let us suppose, I am swimming right now). Suppose now that
we switch systems of beliefs--somehow, you come to have my set of
beliefs and I come to have yours. Given that coherence is entirely a
matter of relations among beliefs, your system will be as coherent in
my mind as it was in yours, and vice-versa. And yet, our beliefs are
now completely unjustified--there you are, reading, believing
that you are swimming, and here I am, swimming, believing that I am
reading. In other words, certain transformations that preserve
coherence in a system of beliefs do not seem to preserve
justification.



In reply, coherentists have argued that it is possible to give
experience a role without sacrificing the idea that coherence is
entirely a matter of relations among beliefs--one idea is to
require that any minimally acceptable system of beliefs contain
beliefs about the experiences that the subject is undergoing (see
BonJour 1985 and Lehrer 1990). It is fair to say that there is no
agreement regarding whether this move can solve the problem.


### 5.4 Rejecting Premise 7: Positism



One position that can be traced back to some ideas in
Wittgenstein's *On Certainty* (Wittgenstein
1969)--and, perhaps, also to Ortega's *Ideas y
Creencias* (Ortega y Gasset 1940)--is that evidential chains
have to terminate in beliefs that are not properly said to be either
justified 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 that
inferential chains have to be finite and non-circular. But, whereas
the foundationalist thinks that the starting points of inferential
chains are beliefs that are justified by something other than beliefs,
the positist thinks that the starting points of inferential chains are
beliefs that are not justified by anything--they are posits that
we have to believe without justification. Despite this difference
between the positist and the foundationalist, the positions are
structurally similar enough that analogues of the questions posed to
the foundationalist can be asked of the
 positist.[21]



First, then, which beliefs are such that they are not justified and
yet are the starting points of every inferential chain--in other
words, how do we identify which are the posits? One answer that can be
gleamed from Wittgenstein's *On Certainty*, which we will
call "relativistic Positism", is that this is a matter
that is relative both to time and society, because what the posits are
is determined by some function of the actual positing practices of the
members of one's society at a certain time. Thus, according to
Wittgenstein, the proposition that no one has been to the moon was a
posit for a certain long period of time--it was a proposition
that no one felt the need to justify, and that was presupposed in many
justificatory practices. For obvious reasons, though, that proposition
can no longer appropriately function as a posit. Other
epistemologists, "non-relativistic positists", think that
which beliefs are properly posited depends on some objective truth
about which beliefs have to be presupposed in order to engage in the
practice of justifying beliefs at all. One prime candidate for playing
this role is the first-person belief that I am not being deceived by
an evil demon into thinking that I am a normally embodied and situated
human being (this is the view advocated by Wright 2004 that we already
alluded to in section 3.2).



The second question, regarding how posits must be related to inferred
beliefs in order to justify them, can receive answers that are
completely analogous to the foundationalists'.



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



One objection that positists of both sorts have to face is that they
are transforming a doxastic necessity into an epistemic
virtue--that is, they are concluding that certain beliefs can
properly serve as the starting points of inferential chains because
that is how in fact they are treated (relativistic Positism) or
because otherwise it wouldn't be possible to engage in
inferential practices at all (non-relativistic Positism). The
Pyrrhonian skeptic, of course, will reply that the mere fact that most
members of a society accept a certain belief without justification, or
even the fact that if we don't do so then we cannot justify
anything else, doesn't mean that it should be accepted without
justification.


### 5.5 Rejecting More than One Premise



Perhaps the most interesting recent development in relation to
Pyrrhonian Skepticism is that more and more epistemologists are
arguing that the proper way to reply to Agrippa's trilemma is to
combine some of the positions that, for ease of exposition, we have
presented as mutually exclusive. Thus, for example, many contemporary
epistemologists put forward theories that contain elements of both
Foundationalism and Coherentism (see, for instance, Haack 1993). It is
a testament to the endurance of Pyrrhonian Skepticism that
philosophers continue in this way to grapple with it.