## 1. The Central Questions



The core concepts of ancient skepticism are belief, suspension of
judgment, criterion of truth, appearances, and investigation.
Important notions of modern skepticism such as knowledge, certainty,
justified belief, and doubt play no or almost no role. This is not to
say that the ancients would not engage with questions that figure in
today's philosophical discussions. Ancient debates address
questions that today we associate with epistemology and philosophy of
language, as well as with theory of action, rather than specifically
with the contemporary topic of skepticism. They focus on the nature of
belief, the relationship of belief to speech and action, and the
mental states of inquiry (on the role of ancient skepticism throughout
the history of Western philosophy up to today, cf. Lagerlund 2020; on
the relation between ancient skepticism and philosophical debates
today, cf. Machuca and Reed 2018, Vlasits and Vogt 2020, and Machuca
2022).



From the point of view of the ancient skeptics, assertions are
expressions of dogmatism. And yet, the best-known ancient skeptic,
Sextus Empiricus, wrote extensively. Can the skeptics say anything
meaningful about their philosophy without asserting anything about how
things are (Bett 2013, 2019)? Skeptical writings have a peculiar
format, one that comes with its own challenges: the skeptics aim to
describe their philosophy *tout court*, as they practice it,
without laying out any particular theories or doctrines. Skeptical
ideas have been charged with a family of objections: they might be
self-refuting, inconsistent, self-contradictory, and so on (Castagnoli
2010). Another line of objection is associated with Hume, namely that
"nature is always too strong for principle." As Hume puts
it, "a Pyrrhonian cannot expect that his philosophy will have
any constant influence on the mind" (part 2 of section 12,
"Of the Academical or Sceptical Philosophy," *An
Enquiry Concerning Human Understanding*, London, 1748). It is one
thing for skepticism to be coherent. It is another thing for it to be
likely that anyone, no matter how much they rehearse skeptical
arguments in their mind, will succeed in adhering to it (Johnson
2001), as ancient Pyrrhonist philosophers claimed to be able to
do.



Like later epistemologists, the ancient skeptics start from questions
about knowledge. But discussion quickly turns to beliefs (Fine 2000).
The Greek term translated here as belief, *doxa*, can also be
translated as opinion. The root of *doxa* is *dokein*,
seeming. In a belief, something seems so-and-so to someone. But there
is also an element of judgment or acceptance. The relevant verb,
*doxazein*, often means 'to judge that something is
so-and-so.' Hellenistic discussions envisage three attitudes
that cognizers take to impressions (how things seem to them): assent,
rejection, and suspension of judgment (*epoche*).



Suspension is a core element of skepticism: the skeptic suspends
judgment. However, if this means that the skeptic forms no beliefs
whatsoever, then skepticism may be a kind of cognitive suicide.
Arguably, belief-formation is a basic feature of human cognitive
activity. It is not clear whether one can lead an ordinary human life
without belief, or indeed, ancient opponents of the skeptics say,
whether one can even survive. Perhaps even the simplest actions, such
as eating or leaving a room without running into a wall, involve
beliefs (Annas-Barnes 1985, 7; Burnyeat 1980). It is also hard to say
whether someone who succeeded in not forming any beliefs could
communicate with others, whether they could engage in philosophical
investigation, or whether they could even think at all.



The ancient skeptics are well aware of these objections. The most
widely discussed charge is that they cannot act without belief
(Apraxia Charge). In response, the skeptics describe their actions
variously as guided by the plausible, the convincing, or by
appearances. The notion of appearances gains great importance in
Pyrrhonian skepticism, and poses difficult interpretive questions
(Barney 1992). When something appears so-and-so to someone, does this
for the skeptics involve some kind of judgment on their part? Or do
they have in mind a purely phenomenal kind of appearing? The skeptical
proposals (that the skeptic adheres to the plausible, the convincing,
or to appearances) have in common their appeal to something less than
full-fledged belief about how things are, while allowing something
sufficient to generate and guide action.



However, the claim that ancient skepticism is about belief, while
modern skepticism is about knowledge, needs to be qualified. Ancient
skepticism is not alone in being concerned with belief. Descartes
speaks repeatedly of demolishing his opinions (for example,
*Med* 2:12, *AT* 7:18; cf. Broughton, 2002,
33-61). Contemporary epistemology often pays equal attention to
the notions of both belief and knowledge. The distinctive focus
of ancient skepticism on belief becomes clearer once we consider a
third concept that figures centrally in ancient discussions: the criterion
of truth. The skeptics and their opponents discuss how one
recognizes a true impression as true. Are there some evident things
(some kind of impressions), which can be used as standards or
criteria, so that nothing is to be accepted as true if it is not in
agreement with these evident things? The Stoics and Epicureans
formulate theories that conceive of such criteria. The skeptics
respond critically to their proposals. Accordingly, the conception of
a criterion of truth assumes as central a role in ancient debates as
does the notion of knowledge in modern discussions. This debate
includes in-depth analysis of sense perception and its relation to
belief. According to Epicurus, all sense perceptions are true, but
judgments based on these perceptions are true or false (Striker 1977,
Vogt 2017). The Stoics explore differences between sense perception,
illusion, and hallucination (Vasiliou 2019). Their account of the
criterion of truth starts from perceptual impressions that qualify, or
fail to qualify, as cognitive (Shogry 2018). The Stoics propose that
we should accept only cognitive impressions, and accordingly we should
only form beliefs based on a subset of true perceptual
impressions.



Discussion of the criterion of truth arguably also covers some of the
ground that is later discussed in terms of certainty. The Stoics say
that a particular kind of impression is the criterion of truth: the
cognitive impression. Cognitive impressions make it clear through
themselves that they reveal things precisely as they are. This notion
is an ancestor to the later conception of clear and distinct
impressions, and thus, to discussions of certainty.



Consider next the notion of doubt. Doubt is often considered the
hallmark of skepticism. So how can it be that ancient skepticism is
not about doubt (Corti 2010, Vogt 2014a)? Insofar as 'to
doubt' means no more than 'to call into question,'
the ancient skeptics might be described as doubting things. However,
skeptical investigation as Sextus Empiricus describes it does not
involve doubt (I shall focus here on Pyrrhonism; on Cicero's use
of *dubitari*, see Section 3.3). Skeptics find themselves
struck by the discrepancies among impressions. This experience is
described as turmoil (Machuca 2019). They aim to resolve this
disturbance by settling what is true and what is false among them. But
investigation leads them to suspension of judgment, which brings its
own peace of mind (*Outlines of Skepticism* [= *PH*]
1.25-30). Where in this account should we locate doubt? Is the
initial turmoil the ancient skeptic experiences a kind of doubt? Are
the ancient skeptic's investigations a kind of doubting? Should
we describe suspension of judgment as a kind of doubt? All three
stages may resemble doubt, at least insofar as the ancient skeptics
have not settled on answers to the questions they investigate. But all
three stages are also different from doubt as it is conceived in later
epistemology. The ancient skeptics do not describe themselves as
making an active effort at doubting what ordinarily they would
believe, as some philosophers in the Cartesian tradition have it.
Instead the ancient skeptics find themselves in turmoil because of
discrepancies in how things strike them. Moreover, the progression
that ancient skeptics describe differs from the doubt-belief model
that later thinkers tend to employ. The ancient skeptics improve their
psychological condition by moving from turmoil to suspension of
judgment, not by removing doubt. It seems best, then, to refrain from
invoking the modern conception of doubt as at all fundamental in the
reconstruction of ancient Greek skepticism.



Some of the distinctness of ancient skepticism lies in the fact that
it is developed by philosophers who genuinely think of themselves as
skeptics. In later epistemology, skepticism is largely construed from
the outside. In particular, early modern skepticism is, for the most
part, conceived by philosophers who aim to refute it. But ancient
skepticism is explored by skeptics, and that is, by philosophers who
intend their lives to be reflective of their philosophy (Cooper 2012
ch. 5.5-7; Bett 2013b). Socrates raises the challenge that it
might be truly bad (for one's life, for the state of one's
soul, and so on) to base one's actions on unexamined beliefs.
For all one knows, these beliefs could be false, and without
investigation, one does not even aim to rid oneself of false belief,
which is admittedly a bad thing for one's soul. Only an examined
life is worth living (Cooper 2007). Once we take this challenge
seriously, as the ancient skeptics do, we embark on a kind of
investigation that is seen as directly relevant to our lives. Our
beliefs are assumed, at this pre-skeptical phase, to be guiding our
actions. Confidence in unexamined views seems misplaced. Others
regularly disagree with us. In favor of each view, some arguments
can be adduced, some practices invoked, some experiences cited. These
conflicting arguments, practices and experiences need to be examined.
But that just raises further views that are in conflict. As a
consequence, suspension of judgment on every such question looks
rationally mandatory. But it is also rational to persist in
investigation. The skeptic is committed to a search for the truth, on
virtually all questions, even if this search repeatedly and
predictably leads to suspension of judgment (Cooper 2012).


## 2. Skeptical Ideas in Early and Classical Greek Philosophy


### 2.1 Early Greek Philosophy



The early Greek philosophers develop distinctions between reality and
appearances, knowledge and belief, and the non-evident and the
evident. These distinctions form the framework in which skepticism can
be conceived. The idea that truth is seen and knowledge gained from
some perspective outside of the ordinary ways of mortal life, and that
mortals rely on something lesser, be it the hear-say of fame, or
signs, or appearances, runs through much of early Greek thought.
However, few early Greek thinkers seem to have had skeptical or
proto-skeptical inclinations. Xenophanes and Democritus are perhaps
the most prominent apparent exceptions.



Xenophanes famously insists that all conceptions of the gods are
anthropomorphic and culturally contingent (DK 21B14, B15). The
Ethiopians pray to gods who look like Ethiopians, the Thracians to
gods who look like Thracians (B16). If horses and cows had hands, the
horses would draw pictures of gods that look like horses, and the cows
would draw gods as cows (B15). Xenophanes puts forward a number of
theological theses of his own. But he says that no man will know the
clear truth about such matters. He makes a point that has lasting
relevance in discussions of skepticism: even if someone succeeded in
saying something that actually is the case, he himself would not know
this. Thus, all is belief (120: B34) (cf. Sassi 2011 on
interpretations of Xenophanes that influence the history of
skepticism).



Atomism--a theory which thrives in Hellenistic times as the
physical theory of Epicureanism, and is thus an interlocutor of
skepticism--leads into difficult epistemological questions. The
atomist can argue that sense perceptions are explicable as complex
events, initiated by objects each one made up of a lot of atoms
floating in the void, from which atoms proceed and traverse the
intervening space, and affect the senses. It is certain objects, made
up by the atoms proceeding from the objects in question (filmy images)
that we actually perceive. We neither perceive 'real
reality' (atoms and void), nor even macroscopic objects and
their properties (for example, a square tower). Democritus seems to
have argued along these lines (SE *M* 7.135-9; cf. fr. 9,
SE *M* 7.136; Theophrastus, *De Sensibus* 2.60-1,
63-4), and accordingly his atomist view of perception can be
seen as grounding a kind of proto-skepticism.



Democritus' student Metrodorus of Chios says at the beginning of
his book *On Nature* "None of us knows anything, not even
this, whether we know or we do not know; nor do we know what 'to
not know' or 'to know' are, nor on the whole,
whether anything is or is not" (Cicero, *Acad*. 2.73;
trans. Lee (2010) = DK 70B1; SE *M* 7.48, 87-8; Eusebius,
*Praep. evang.* 14.19.9). This formulation reflects awareness
of the fact that a simpler statement than the one reported in Cicero,
such as "there is no knowledge," can be turned against
itself. In particular, Metrodorus recognizes the role that
understanding concepts plays in any such statement. Does its proponent
know something, merely by virtue of understanding what the terms she
uses in her philosophizing refer to? Sextus presents Metrodorus'
pronouncement as related to an enigmatic idea that he ascribes to two
other philosophers, the Democritean Anaxarchus of Abdera and the Cynic
Monismus (SE M 7.87-88). Both are said to have likened existing
things to a stage-painting. This comparison, which Burnyeat captures
in the catch-phrase "all the world's a
stage-painting," is open to a range of interpretations (Burnyeat
2017). For Monismus, Burnyeat argues, it is likely to have had a
moralistic upshot, along the lines of "all is vanity." In
Democritean philosophy, and insofar as later skepticism recalls the
saying, it is bound to be a proposal in epistemology (or possibly
epistemology and metaphysics).



The 5th century sophists develop forms of debate which are
ancestors of skeptical argumentation (Bett 2020b). They take pride in
arguing in a persuasive fashion for both sides of an issue and
in developing an agonistic art of refuting any claim put forward.
Further, the sophists are interested in the contrast between nature
and convention. The formative roles of custom and law were discussed
by some of the earliest Greek authors (consider Pindar's
"law is king" and its many interpretations, for example in
Herodotus). The sophists explore the idea that, if things are
different for different cultures, there may be no fact of the matter
of how those things really are. The skeptics engage with both legs of
the distinction between nature and convention. Pyrrhonian skepticism
employs an argument to the effect that, if something is by nature
*F*, it is *F* for everyone (affects everyone as
*F*) (see sections 4.2 and 4.4). Pyrrhonism further associates
convention with appearances, so that the sceptic, by adhering to
appearances, can lead an ordinary life (see section 4). However, the
contrast between nature and convention does not figure importantly in
ancient skepticism, and there is no skeptical school that would
confine itself to 'moral' skepticism, or skepticism about
values.



Sextus Empiricus, whose writings provide the most detailed extant
account of Pyrrhonian skepticism, emphasizes how strongly the skeptics
depart from all other philosophers. As he presents it, the
Pre-Socratics who put forward some of the views cited above are what
he calls dogmatists. They make claims about nature, reality,
knowability, and so on. The second-most detailed extant account of
Pyrrhonian skepticism is offered by Diogenes Laertius, in his
*Lives of Eminent Philosophers* 9.61-116. It contains a
large number of references to early Greek poets and Pre-Socratic
philosophers, suggesting that these early thinkers formulate ideas
that are similar to skeptic ideas (SSSS61-73). It is
controversial whether the skeptics Diogenes has in mind claim this
ancestry. Alternatively, other philosophers may have charged the
skeptics with sharing ideas with non-skeptical thinkers, thereby
departing from their non-dogmatic approach (Warren 2015). Either way,
two observations seem relevant. Contrary to a classic assessment of
Diogenes' report by Jonathan Barnes (1992), the sections of text
in which connections are made between early Greek thought and
skepticism may be worth exploring. Moreover, scholars may have paid
too little attention to skepticism's ancestry in poetry (Clayman
2009). Pyrrho seems to have referred to Homer as a proponent of ideas
he approves of, ideas about change, the status of human rationality
and language, and more.


### 2.2 Plato



The Socrates of Plato's *Apology* tries to solve a
puzzle. The Delphic oracle says that no one is wiser than Socrates.
But Socrates does not think himself wise. He calls into question the
truth of neither the oracle's pronouncements nor his
self-perception. Accordingly, he must figure out how both are
consistent with each other. In order to do so, Socrates talks to
various groups of experts in Athens: politicians, poets, and
craftsmen. As it turns out, all of them think that they know something
about great and important things, but in fact, it seems clear to
Socrates, they do not. When asked they cannot provide reasons for
believing the things they claim to know that are rationally
satisfactory. Socrates knows that he does not know about these most
important matters (*megista*; 22d); his interlocutors, it
appears, do not know that they lack this knowledge. In this respect,
Socrates is wiser than everyone else who has any general reputation
for wisdom. In the course of recounting his conversations with others,
Socrates says something enigmatic: "About myself I knew that I
know nothing" (22d; cf. Fine 2008). Some readers (ancient and
modern) take Socrates to profess that he knows nothing. But the
context of the dialogue allows us to read his pronouncement as
unproblematical. Socrates knows that he does not know about important
things. He advocates the importance of critically examining
one's own and others' views on important matters,
precisely because one does not know about them (Vogt 2012a, ch. 1).
Such examination is the only way to find out.



Socrates' commitment to reason--examination as the way to
find out--inspires the skepticism of the Hellenistic Academy
(Cooper 2004b, Vogt 2013). One is bound to lead one's life based
on one's beliefs, he assumes. Therefore, one ought to examine
one's beliefs, and abandon those that one finds to be false. One
ought to do so because otherwise one might lead a bad life.
Socrates' questioning is rooted in a concern with the good life.
Insofar as it is, one might think that the Socratic roots of ancient
skepticism lead one toward a kind of limited, wholly moral skepticism.
However, Socrates' examinations are not confined to value
questions. While ethical questions may be the starting-point, they
immediately lead to questions about the soul, the gods, knowledge, and
so on. For Socrates and his Hellenistic followers, value questions
cannot be insulated from questions of psychology, physics, and
epistemology.



Another strand of skeptical thought begins with questions about the
nature of philosophical investigation. In the *Meno*, Plato
formulates a famous puzzle. How is investigation possible? We cannot
investigate either what we know or what we do not know. In the former
case, there is no need to investigate, and besides, if we really do
know we already have in mind everything that investigation could
reveal to us about the matter. In the latter case, we would not know
what to look for, and we would not recognize it if we found it
(80d-86c). So there is no room for investigating anything. Socrates
calls this an eristic argument, thus drawing attention to the fact
that this is a puzzle that sophists have put forward (cf.
Plato's *Euthydemus*).



Plato's solutions to this puzzle are difficult to assess (Fine
2014). Learning is recollection, says one proposal (this is the one
that Socrates himself immediately offers). We already know, but only
in some implicit way, what it takes investigation to come to know
explicitly. This is the famous Anamnesis theory (81a-d). If we give up
on investigation, we shall be lazy people, says another argument
(81d-e). A third solution of the puzzle arguably says that one of its
premises is false. It is not the case that, for everything, we either
know it or are entirely ignorant of it. Rather, there is a third
state, namely belief (83a-86a). Investigation can begin from
beliefs.



The *Meno* explores a mix of these solutions. Plato develops
what he calls a hypothetical method (86c-100b). That is, the
interlocutors in some sense begin from their beliefs (for example,
"virtue is good"). But they do not endorse them. They set
them up as hypotheses, and employ these hypotheses in investigation
(on the relationship between Pyrrhonian skepticism and Plato's
and Aristotle's notions of hypothesis, cf. Corti 2011). A
spurious dialogue, the *Sisyphus*, discusses a similar puzzle,
though with respect to deliberation. Deliberation either involves
knowledge or is mere guesswork; either way, deliberation is
impossible. Here, too, we may ask whether the distinction between
knowing and not knowing is exhaustive, or whether attention to belief
changes the picture (Fine 2021, ch. 8).



Plato discusses and re-formulates several of the metaphysical
considerations that back up proto-skeptical and early skeptical
intuitions. The relevant passages are spread out over a number of
dialogues, among which passages in the *Phaedo*,
*Republic*, *Theaetetus* and *Timaeus* are
perhaps most important. In these dialogues, Plato develops some of his
own metaphysical ideas. He also engages critically with metaphysical
theories that he does not ultimately adopt. However, in order to
explore these theories he formulates them in detail, often invoking a
Pre-Socratic ancestor as a proponent of a given idea. These
discussions are a great source of inspiration for Pyrrhonian skeptics,
who are interested in what may be called a metaphysics of
indeterminacy (Bett 2000, Vogt 2021).



In contrasting the Forms with the perceptible realm, Plato discusses
properties. For example, for all sensible items, *A* is tall
relative to some *B* and short relative to some *C*.
There is no such thing as anything's being tall
*simpliciter*. When we call something tall, we measure it
against something else, look at it from a particular perspective, and
so on. As we might say, "tall" and "short"
are relative predicates. But perhaps many more, or indeed all,
predicates work that way, even where this is less obvious.
Plato's arguments lead to the question of whether it is
conceivable that all our predications are, in this particular sense,
relative. If this were the case, it might quite fundamentally upset
our conception of the world as furnished with objects that have
properties. Such considerations lead to another idea about properties
in the perceptual realm. If a fence is low and high, a cloud is bright
and dark, a vase beautiful and ugly, and so on, then it seems that,
perhaps quite generally, perceptual things are *F* and
not-*F*. Only the Form of *F* is *F* (for
example, only the Beautiful is beautiful). While the relevant passages
are difficult to interpret, it is clear enough which line of thought
comes to influence later skeptics. The skeptics engage with the idea
that, if something appears to be *F* and not-*F*, it is
not really (or: by nature) either *F* or not-*F*.



In the *Timaeus*, Plato argues that an account of the natural
world can only be 'likely': it is an *eikos
logos*. Most generally speaking, the idea here is that certain
explananda are such that theorizing about them can do no more than
mirror their, comparatively speaking deficient, nature. This idea has
ancestors in Xenophanes and Parmenides, and it plays a crucial role in
the *Timaeus* (Bryan 2012). Academic skeptics employ various
notions of the plausible and the convincing, thus developing further
this tradition, albeit no longer with the assumption that different
domains require different kinds of theorizing.



In the *Theaetetus*, Plato explores the kind of cultural
relativism that is associated with some sophists. In his examination
relativism is extended to a general theory, not restricted to the
domain of values. Socrates (as main speaker of the dialogue) ascribes
relativism to Protagoras, who is famous for saying that "man is
the measure." Socrates reformulates this claim as follows: what
appears to *A* is true for *A*, and what appears to
*B* is true for *B*. On this premise, Socrates argues,
there is no rational way to prefer our perceptions while awake to our
perceptions while asleep, or similarly, to prefer sober to intoxicated
or deranged perceptions. In each state, our perceptions are true for
us. Socrates analyzes relativism in several steps, pointing to ever
more radical implications. Along the way, he envisages a moderate
metaphysics of flux, where objects do not have stable properties. But
eventually he points out that relativism is committed to an even
starker revisionist metaphysics, radical flux. For it to be possible
that what seems to *A* is true for *A*, and what seems
to *B* is true for *B*, there cannot be a stable world
that *A* and *B* both refer to. Rather,
"everything is motion" (*Tht.* 179c-184b). The
skeptics employ versions of some of the arguments in the
*Theaetetus*, without, however, arriving at relativist
conclusions. Schematically speaking, the relativist says that,
if *X* is *F* for *A* and *F*\*
for *B*, then *X* is *F*-for-*A* and
*F*\*-for-*B*. Pyrrhonian skepticism of the variant found
in Sextus reacts by continued investigation into whether *X* is
*F* or *F*\* (or both or neither).


### 2.3 Aristotle



Aristotle engages, at several points in his works, with the
*Meno* Problem. For example, Aristotle points out that, for
successful investigation to proceed, one first needs a well-formulated
question. One needs to know the knot in order to untie it. In order to
know what to look for and recognize it when one finds it, one needs to
first think one's way through the difficulties involved, and
thereby formulate a question. If one does, then one shall be able to
recognize the solution once one hits upon it (*Met.* 3.1,
995a24-b4). These ideas are highly relevant to Hellenistic
discussions. The skeptic is an investigator, and one anti-skeptical
charge says that, if indeed a skeptic knew nothing, they could not
even formulate the questions they investigate. Interpreters have
emphasized a contrast between Aristotle and the skeptics. For
Aristotle, formulating puzzles and thinking one's way through
them puts one in a better position, such that one gets clear about how
matters are. This may be different for the skeptics: engagement with
different angles of philosophical problems leads them to suspension of
judgment (Long 2006, Code 2010). Other scholars argue that the
skeptics' way of thinking through puzzles improves their
cognitive condition even though they do not settle for an answer to a
given question (Vogt 2012a, ch. 5). Also, scholars point to modes of
thinking in Plato and Aristotle that are not primarily concerned with
results. In contemplation, a cognizer may think again and again
through the same kinds of matters, and yet doing so presumably
improves their cognitive condition (Olfert 2014).



In *Posterior Analytics* I.1, Aristotle says that all teaching
and learning comes about through things we already know. When we
phrase questions, we already have 'That-Knowledge' and
'What-Knowledge.' For example, when we ask questions about
triangles, we need to know that there are triangles (otherwise we
would not have questions about their properties). We also need to have
a notion of what triangles are (we draw a triangle, not a square, when
we phrase a question about its properties). Another way in which
Aristotle addresses the *Meno* Problem conceives of particular
perceptions as the starting-points of investigation. Complex cognitive
activities arise from simpler ones. Many particular perceptions lead
to memory, to experience, and eventually to expert understanding
(*Met.* 1.1, *An. Post.* II.19). With the
generalizations of memory, experience, and expertise comes the ability
to investigate. With respect to skepticism, the important point here
is that the starting-points of investigation are not themselves in
need of justification.



Like Plato, Aristotle engages with the Protagorean claim that, as
Aristotle puts it, all seemings (*dokounta*) and appearances
(*phainomena*) are true (*Met* 4.5). If this were so,
Aristotle says, everything would have to be true and false at the same
time. Aristotle argues that earlier thinkers arrived at such views
because they identified being solely with the perceptual (4.5,
1010a1-3). Caught up in this assumption, they did not see who or
what was going to judge between conflicting sense perceptions. For
example, it seemed unsatisfactory to dismiss the views of sick and mad
people simply on the grounds that they are in the minority, thereby
considering as true what appears to the greater number of people.
Similarly, Aristotle reports that these earlier thinkers looked at the
ways in which things appear differently to different kinds of living
beings, and to one person at different times (4.5,
1099b1-11).



In *Metaphysics* 4.4, Aristotle notes that some people consider
it possible for the same thing to be and not to be, and for someone to
believe so (he refers to a range of positions, all of which in some
way are related to denial of the Principle of Non-Contradiction; see
Castagnoli 2010, I.5.4). Against this, Aristotle says it is the
firmest of principles that things cannot be and not be at the same
time. To deny this shows a lack of training. With adequate training,
one recognizes for which things proof should be sought, and for which
it ought not to be sought (see also *An. Post.* I.3). It is
impossible that there be demonstration for everything. Otherwise
demonstration would go on *ad infinitum*. Scholars often refer
to this point when discussing the skeptical modes of argument. The
skeptics might be guilty of what, from Aristotle's perspective,
would be a mistake of exactly this kind (on this theme in later
Aristotelian logic, cf. Malink 2020).



Aristotle continues in a way that is highly relevant to discussions of
skeptical language and action. A person who wishes to deny that things
cannot be and not be at the same time has two options. Either they say
nothing, or they talk to us. In the first case, there is no need for
us to refute them. This person is like a plant--they do not talk.
In the second case, either their utterance signifies something, or it
signifies nothing. If it signifies something, then they say that
something is so-and-so (which Aristotle takes to be self-defeating for
them). If it signifies nothing, then it does not qualify as speech.
Even though they make an utterance, the person is in effect not
speaking with us (or to themselves). Aristotle also explains the
plant-metaphor in terms of action (1008b10-30). A person who believes
nothing is like a plant because they cannot act. Pursuit and avoidance
testify to the fact that people have beliefs. (On Aristotle and
skepticism, see the papers collected in Irwin 1995.)


## 3. Academic Skepticism


### 3.1 Arcesilaus



With Arcesilaus (316/5-241/0 BCE) and his role as leader of the
Academy (266/268 BCE), Plato's Academy turns skeptical.
Arcesilaus does not refer to himself as a skeptic--this
nomenclature is a later designation. However, Arcesilaus stands at the
beginning of a re-orientation in the history of Platonically inspired
philosophy. He rediscovers Socrates the examiner, arguably based on
his reading of Plato's dialogues (Thorsrud 2018).
Socrates' commitment to investigation, to the testing and
exploring of one's own and others' beliefs, and his
passion for weeding out falsehoods, are the starting-points of his
Academic skepticism (Cicero, *Acad.* 2.74, 1.46). Throughout
the history of this skeptical school, these traits, and the
corresponding commitment to a life guided by reason, remain alive
(Cooper 2004b, Vogt 2013). When, as we shall see below, Arcesilaus
defends a skeptical life without belief, this is because, as he
thinks, reason itself, if properly and faithfully followed, leads us
to live that way. To Arcesilaus, the skeptical life is a life lived
following reason, a life based *on* reason--just as the
competing Stoic and Epicurean lives are alleged by their proponents to
be. Arcesilaus engages with the epistemologies of these contemporaries
of his. In particular, the Academics call into question that there is
a criterion of truth, as both Epicureans and Stoics, beginning in the
generation before Arcesilaus, claim there is. One interpretive
question that concerns Arcesilaus, but also later Academic skeptics,
is especially vexed. According to Seneca (*Letter* 88,
44), the Academics paradoxically claim to know that nothing can be
known. Scholars disagree on how this and similar reports fit together
with the picture of Academic skeptics as open-minded inquirers (Allen
2017). According to Sextus Empiricus, the Academics skeptics say that
everything is inapprehensible (PH 1.226, cf. PH 1.3). Is
"everything is inapprehensible" the single thing that can
be apprehended? Does so-called "non-apprehension"
(*akatalepsia*) amount to the general claim that there is
no knowledge? Alternatively, the Academics may dialectically
appeal to the Stoic notion of *katalepsis*, and argue
merely that the Stoic notion of apprehension is not compelling (Allen
2022).



Like Socrates, Arcesilaus did not write anything. His views must be
unearthed from Sextus' comparisons between Pyrrhonian and
Academic skepticism, from Cicero's discussions in the
*Academica*, and from a range of shorter (and sometimes
hostile) reports. Major themes in Arcesilaus' philosophy are (i)
his dialectical method, (ii) discussion of whether there is a
criterion of truth, and (iii) his defense of the skeptic's
ability to act.



(i) Method. Arcesilaus embraces what scholars call a dialectical
method (Couissin 1929 [1983], Perin 2013, Thorsrud 2018). This method
is inspired by Socrates. It proceeds by asking one's real or
imaginary interlocutor what they think about a given question, then
plunging into an examination of their views, employing their premises.
Can they explain their position without running into inconsistencies,
and without having to accept implications that they want to resist? As
a consequence of this method, it sometimes appears as if a skeptic,
while examining someone's view and its consequences, makes a
positive claim: "so, such-and-such is not so-and-so."
However, within a dialectical exchange, this should be read as
"according to *your* premises, such-and-such
follows." This method remains a key ingredient of Greek
skepticism. While the different skeptical schools develop variants of
the dialectical method, skeptical argument is often characterized by
the fact that skeptics think of themselves as engaging with
"dogmatic" interlocutors. In the skeptical tradition, as
articulated for example by Sextus Empiricus (see section 4.4.),
"dogmatists" are philosophers who put forward, and defend,
positive answers to philosophical questions about reality, knowledge,
ethical values, etc. They need not do so dogmatically or rigidly or
without consideration of alternatives in order to count, in skeptical
terms, as "dogmatists."



(ii) The Criterion of Truth. Zeno, the founder of Stoicism, and
roughly 20-30 years Arcesilaus' senior, was for a time a
student at the Academy. He was still in the Academy when he formulated
key Stoic doctrines. Like Arcesilaus, he claims Socratic ancestry.
Zeno is inspired by some of the same ideas that inspire the skeptics.
In particular, he engages with the Socratic idea that knowledge is
integral to virtue. Contrary to Arcesilaus, Zeno aims to give accounts
of knowledge and virtue, and holds them up as ideals that human nature
permits us to achieve. For him, knowledge is very difficult to attain,
but ultimately within the reach of human beings. From the point of
view of Arcesilaus, Zeno's claim to Socratic heritage is almost
offensive: Zeno seems to be too optimistic about our cognitive powers
to be following Socrates (Frede 1983). Scholars have traditionally
envisaged an exchange of arguments between Zeno and Arcesilaus, where
each modified his views in the light of the other's criticism.
However, Zeno most likely formulated his views between 300-275,
and Arcesilaus argued against him c. 275 to 240, when Zeno (who died
c. 263) was probably already retired (Brittain 2006, xiii; Alesse
2000, 115 f.; Long 2006, ch. 5).



The core of the dispute between Arcesilaus and the early Stoics
concerns the question of whether there is a criterion of truth. The
notion of a criterion is introduced into Hellenistic discussions by
Epicurus, who speaks about the *kanon* (literally
measuring stick) and *kriterion*. For Epicurus, a
criterion is that evident thing, viz., the content of a
sense-perception, against which claims about the non-evident are
tested. For example, physics advances claims about non-evident things,
such as atoms and void. These are not accessible to the senses, and
accordingly, do not count as evident. Perception rules out various
physical theories. For example, a physical or metaphysical theory
according to which there is no movement can be dismissed because it is
in disagreement with the evident.



Zeno argues that a certain kind of impression--namely a cognitive
impression (*phantasia*
*kataleptike*)--is the criterion of truth (cf.
Shogry 2018). Zeno's conception of cognition
(*katalepsis*, literally grasping, apprehension), and the
related notion of a cognitive impression, aim to solve an
epistemological problem. Belief-formation aims at the truth; there is
a norm inherent in the practice of believing that one should only
believe truths. It is not transparent to us, however, which of our
beliefs, or claims to the effect that such-and-such is true, are
successful in their aim and hit the truth. Zeno argues that some
impressions are cognitive. A number of Stoic definitions of the
cognitive impression, formulated by Zeno and his successors, are
transmitted. Scholars approach them in at least three ways. First,
some scholars consider one of the Stoic definitions (SE M 7.247-52) as
canonical (Nawar 2014, Shogry 2018). Two, scholars at times examine
specific exchanges between Stoics and skeptics in the assumption that
some clauses in Stoic definitions respond to skeptic objections (for
example, Nawar 2017). Three, scholars have also pointed out that, here
as elsewhere, the Stoics offer a multitude of definitions, without
privileging one of them as "the" definition; different
definitions may speak to different dialectical contexts or theoretical
foci (Vogt 2022).



With some simplification, a cognitive impression reveals its content
and that it is kataleptic (cf. Cicero, *Academica*
2.77-8). For example, when I look at my computer screen
while typing this, I may very well have a cognitive impression that
this is my computer screen. When I look up and out of the window, I
have an impression of a friend walking across campus that is probably
non-cognitive. This impression might be true. But since I see her from
such a distance, it is pretty surely not cognitive. That is, not all
true impressions are cognitive, but all cognitive impressions are
true. We should only assent to cognitive impressions, and so in
forming our beliefs, hold only those certified beliefs (cf. Brittain
2014 on the Stoic view that assent to cognitive impressions is not
compelled).



Arcesilaus calls into question whether there are impressions of this
kind. His main point seems to be that there could be an impression
that is phenomenologically indistinguishable from cognitive
impressions, but nevertheless misrepresents the matters it gives an
impression about. To use an example that may derive from Carneades
(see section 3.2), there is no impression of a given egg such that no
impression of any other egg could be phenomenologically
indistinguishable from it (Shogry 2018 and 2021, Machek and Veres
forthcoming). Assuming that some clauses in Stoic definitions respond
to specific skeptic challenges, the following clause, added to a
shorter definition, appears to speak to these cases: "and
of such a kind as *could* not arise from what is not"
(Long and Sedley (1987) [= LS] 40; DL 7.46, 54; Cicero *Acad*.
1.40-1, 2.77-8; SE *M* 7.247-52). Absent a
criterion of truth, Arcesilaus' skeptic suspends judgment about
everything (*PH* 1.232). Reason itself, Arcesilaus thinks,
demands such suspension.



(iii) Action. If skeptics suspend judgment, argues their dogmatic
opponent, they are not able to act. Stoic philosophy conceives of
three movements of the mind: impression, assent, and impulse
(Plutarch, *Col.* 1122a-d). All three figure in action. The
agent assents to the impression that *A* is to be done; their
assent is an impulse for the action *A*; if there is no
external impediment, the impulse sets off the action (Inwood 1985). It
is a cornerstone of Stoic philosophy that there can be no action
without assent, and so without the belief that the action done is
*to be* done. The Stoics aim to avoid the kind of determinism
according to which actions are not 'up to' the agent
(Bobzien 1998); for them, assent, but not impression, is up to the
agent. In response to the Apraxia Charge, Arcesilaus seems to have
argued that the skeptic can act without having assented (Plutarch,
*Col.* 1122A-d), and so without believing that the action done
is *to be* done. However, this is not his complete response.
From the point of view of the Stoics, skeptical action, if performed
without the relevant kind of assent (that is, assent that it is up to
the agent to give, and that is a rational acceptance of the
impression), is like the action of a non-rational animal, or like the
automatic movement of plants when they grow and flourish. Arcesilaus
is robbing people of their minds (Cicero *Acad.* 2.37-9;
Obdrzalek 2013). But Arcesilaus need not and does not go so far as to
compare human agents with non-rational agents. As human beings,
skeptics have rational impressions. They perceive the world
conceptually, and think about it. Arcesilaus does not suggest that
skeptical action is causally set off by impressions, or in the way,
whatever that is, that animal actions are set off. This would be a
problematic proposal, for it would disregard that the skeptic has a
human mind. Given the complexity of human thought, the skeptic is
likely to have several, and often competing impressions. If all
impressions triggered impulses, the skeptic would be inactive due to a
kind of paralysis. The second component of Arcesilaus' reply,
thus, is that the skeptic, in acting without assenting, adheres to the
reasonable (*eulogon*) (SE *M* 7.158; 7.150; Striker
2010). That is, Arcesilaus aims to explain skeptic action as rational
agency (Cooper 2004b). Arcesilaus disputes the dogmatic claim that
some impressions can be identified as true, and the related claim that
one can only act on the *belief* that some impression is true.
But he does not argue that there are no differences between
impressions which agents could take into account. His agents are
rational: they think about their options, and go with what looks, in
one way or another, more plausible.



Arcesilaus defends skeptical action also against Epicurean critics
(Plutarch, *Col.* 1122A-d), again by showing on the basis of
the Epicureans' own premises that skeptical action is possible.
Can the sceptic explain why, when leaving a room, they go through the
door rather than running into the wall? Arcesilaus seems to have
exploited the Epicurean view that, while all sense-perception is true,
belief can introduce falsehood. Like the Epicurean, the skeptic can
keep apart the perception and a view formed on its basis. By not
assenting to the perception, thus adding belief ("here is the
door"), the skeptic guards against the source of falsehood,
namely belief. But a skeptic has perception of the door available to
them, which is enough for not running into walls.


### 3.2 Carneades



Like Arcesilaus, Carneades (214-129/8 BCE) refrains from writing
and philosophizes in a Socratic spirit. Carneades led an embassy of
three philosophers from Athens to Rome in 156/5 BCE. Aside from his
official role, he is said to have given two speeches, arguing for
justice one day and against justice the next. Whether or not this is
historically correct (Powell 2013), the traditional take on
Carneades' speeches is not that he aims to overthrow justice.
Instead, the upshot is taken to be that he wants to show that the
supporters of justice--including Plato and Aristotle--do not
have the successful arguments they think they have to show what
justice is and what it requires (Lactantius, *Epitome* 55.8, LS
68M). Like Arcesilaus, Carneades (i) engages with Stoic epistemology.
His account of skeptical action includes (ii) a detailed proposal
regarding the criterion. As part of his less radical skepticism,
Carneades seems (iii) to allow for a certain kind of assent, and
perhaps for belief.



(i) The Stoic-Academic Debate. Chrysippus, the third major Stoic
(after Zeno and Cleanthes), and his student Diogenes of Babylon,
revise Zeno's epistemology, defending it against
Arcesilaus' arguments (Brittain 2006, xiii). In response to
their arguments, Carneades continues the exchange with the Stoics that
Arcesilaus began (SE *M* 7.402-10). His first move
addresses the link between mental states and action. People in states
of madness, he argues, act just as easily and naturally on their
impressions as other people, even those who act on cognitive
impressions (if there are any). From the point of view of exhibited
behavior, there does not seem to be a difference: any and all
impressions, even those the Stoics think clearly arise from something
that is not, are in all respects relevant to action completely on a
par. Cognitive impressions, if there are any, have no superiority.



In a second argument, Carneades points to objects that are similar to
one another: can the wise person discern any two eggs, two grains of
sand, and so on? The Stoics have multiple replies. It is conceivable
that, in some contexts of action, the wise person assents to what is
reasonable (*eulogon*) (DL 1.177), without having a cognitive
impression of how things are. Or, if faced with the task to identify
grains of sand while lacking a cognitive impression, the wise person
can suspend judgment. However, the wise will train themselves so as to
be able to perceive minute differences (Cicero, *Acad*. 2.57),
where it might be important to do so. This point is backed up by Stoic
physics: no two items in the universe are identical, and their
differences are in principle perceptible (Sedley 1982, 2002).
Carneades replies that even if no two things were exactly alike
(consistent with his general line of argument, he does not take a
stance on such questions), a very close similarity could appear to
exist for all perceivers (Cicero, *Acad*. 2.83-5); that
is, the impressions of two items, though in fact these items might
differ from each other, could be indistinguishable (Nawar 2017, Shogry
2018 and 2021). Discussion continues with a move on the part of the
Stoics: they add to their definition of the cognitive impression
"one that has no impediment." Sometimes an impression
is--as it were, by itself--cognitive, but is unconvincing
due to external circumstances (SE *M* 7.253). It is a difficult
question whether this addition harms the Stoics more than it helps
them. If the initial conception of a cognitive impression hangs on the
idea that something about its phenomenological nature, or something
internal to the impression, marks it as cognitive, the Stoics give up
on a crucial assumption if they grant that sometimes there are
"impediments." If, however, cognitive impressions are
differentiated by a causal feature (the way they are caused by the
'imprinter' which causes the 'imprint'), the
further addition might help (Frede 1983, Nawar 2014), since the
impediment might need to be removed before the causal connection could
be confirmed (Hankinson 2003).



(ii) Carneades' Criterion. Even though Carneades further pursues
a discussion begun by Arcesilaus, he does not simply continue within
the framework of Arcesilaus' skepticism. The distinctiveness of
his position is best seen in the context of his criterion: the
persuasive (*pithanon*). The notion of the persuasive can be
understood in two distinctively different ways. Persuasiveness might
be a causal feature, so that a persuasive impression sets off a
physiological process of being moved in a certain way. But there may
also be a rational kind of persuasiveness. Carneades construes
persuasiveness in rational terms. For him, the persuasive is the
convincing, or perhaps even the plausible.



Carneades develops a three-stage criterion: (1) In matters of
importance, skeptics adhere to the persuasive. (2) In matters of
greater importance, they adhere to the persuasive and undiverted. A
persuasive impression is undiverted if there is no tension between it
and its surrounding impressions. (3) In matters that contribute to
happiness, skeptics adhere to persuasive, undiverted, and thoroughly
explored impressions. A persuasive impression is undiverted and
thoroughly explored when it and the surrounding impressions are
closely examined without its persuasiveness being diminished (SE
*M* 7.166-84). Consider an example. A skeptic looks in a
dark room for a rope. Before they pick up what appears to them to be a
rope, they look closely and poke it with a stick. Coiled objects can
be ropes, but they can also be snakes. The persuasive impression that
this is a rope must be examined before the skeptic adheres to it
(*M* 7.187).



The three-stage criterion is put forward in the context of action.
However, Sextus describes Carneades' criterion as a criterion of
truth, not a criterion of action (*M* 7.173). Carneades might
take himself to offer more than a practical criterion. His discussions
of the persuasive come close to a general epistemological theory
(Couissin 1929 [1983], Striker 1980, Bett 1989 and 1990, Allen 1994
and 2004 [2006], Brittain 2001). Cicero renders the Greek
*pithanon* as *probabile* (and sometimes as *veri
simile*), which modern editors sometimes translate in terms of
what is probable or likely to be true. Some scholars think that
Carneades is an early thinker about likelihoods, and argue that he
develops a fallibilist epistemology (Obdrzalek 2004).



(iii) Assent and Belief. Does adherence to persuasive impressions
involve belief? Carneades coins a term for the kind of adherence he
has been describing: approval (Cicero, *Acad.* 2.99). He
distinguishes it from assent in the sense of Stoic and other dogmatic
theories, which establishes a belief that something is in actual fact
true; but he nevertheless describes it as a kind of assent (Cicero,
*Acad*. 2.104). Carneades' disciples disagree on whether
approval is any kind of genuine assent. That is, they disagree on
whether, in approval, one forms a belief. Philo and Metrodorus think
that Carneades allows for some kind of belief, close to or identical
with belief as the Stoics understand it. Clitomachus disagrees, and
Cicero follows Clitomachus (*Acad.* 2.78, see also 2.59, 2.67).
Scholars continue to debate these issues (Allen 2022), and the basic
problem remains unchanged. It is not clear whether there is a
plausible notion of belief according to which belief falls short of
'holding to be true' (or according to which, though some
kind of 'holding true' is involved, the relevant
affirmation-as-true is weaker than in beliefs as Stoics and other
dogmatist epistemologists conceive of them). In any event,
affirmations as true, at least of the full and flat-out ("in
actual fact") sort the Stoics think of, are precisely what the
skeptic does not make.



Another approach to Carneades' stance toward belief is to ask
whether he might invoke Platonic considerations. Consider that
Socrates, when asked in the *Republic* what he thinks the good
is, refuses to reply because he thinks beliefs without knowledge are
shameful (*Rp.* 506c). In response to this, his interlocutors
point out that there is a difference between putting forward
one's beliefs as if one knew them to be true, and putting them
forward with the proviso that they are merely beliefs (Vogt 2012a, ch.
2). The shamefulness of mere belief might disappear through this
proviso. A passage in Cicero's *Academica* suggests that
Carneades invokes this thought. According to Carneades, the wise
person can hold beliefs if they fully understand them to be beliefs
(2.148). Along similar lines, it has been suggested that Carneades
might conceive of a hypothetical mode of believing (Striker 1980
[1996, 112]), perhaps engaging with a move in Plato's
*Meno*. Investigation cannot get off the ground if we do not,
in some sense, begin with our beliefs about the matter under
investigation. But how can we do so without endorsing our beliefs, not
knowing whether our views are true? Plato's answer at this point
is: by hypothesizing our beliefs. Today we would insist that
hypotheses are not beliefs. However, it is conceivable that Carneades
argued along these lines, and that the details of his vocabulary got
lost or confused in doxography.


### 3.3 Later Academic Skepticism



Carneades was an enigma to his students and immediate successors.
Clitomachus (head of the Academy from 127 to 110 BCE) seems to have
attempted the impossible: to adhere closely to Carneades'
philosophy, even though he never understood what Carneades truly meant
(Levy 2010). The cornerstone of his adherence lies in the view that
Carneades argues for suspension of judgment and against beliefs
understood as Stoics understand them. Philo of Larissa, another
student of Carneades, interprets his teacher as allowing for tentative
beliefs in the skeptic's life. With Philo, the skeptical era of
Plato's Academy comes to an end. Philo's philosophy seems
to divide into two phases. In Athens, and as head of the Academy, he
stays relatively close to Carneades. Moving to Rome later in his
career, he develops a markedly different position. He argues only
narrowly against the Stoic criterion and their conception of
cognition. One can apprehend things and so come to *know*
them--one just cannot apprehend them in the way in which the
Stoics construe cognition (*PH* 1.235). The fact that there is
no apprehension in the sense of the Stoics does not mean that there is
no knowledge (*Acad*. 2.14). This move shifts the discussion in
several important ways. First, Philo can be interpreted as a kind of
externalist: one can know something without knowing that one knows it.
Absent Stoic cognitive impressions, we are not able to identify which
instances of 'holding-true' qualify as knowledge; but we
nevertheless have some knowledge (Hankinson 2010). Second, this
proposal is a step toward modern skepticism, which is not concerned
with criteria of truth, but with knowledge.



Cicero's skeptical philosophy in his own philosophical writings
is again distinctively different. In line with his notions of what is
probable (*probabile*) or likely to be true (*veri
simile*), Cicero often examines a range of philosophical
positions, aiming to find out which of them is most rationally
defensible. He thinks it is better for us to adopt a view that is
likely to be true, rather than remain unconvinced by either side
(Thorsrud 2009, 84-101). Cicero is of the greatest importance
for the transition between ancient and early modern skepticism. As in
other fields of philosophy, Cicero's influence is partly the
influence of the translator. In transposing philosophical ideas into
the language of a different culture, the ideas change. Cicero
sometimes speaks of doubting, *dubitari* (e.g., *Acad.*
2.27, 106; however, he often sticks with the earlier language of
assent and suspension). But doubt has no place in Greek skepticism
(see section 1).


## 4. Pyrrhonian Skepticism


### 4.1 Early Figures: Pyrrho and Timon



When comparing Pyrrhonian and Academic skepticism, two topics stand
out: Pyrrhonism aims at tranquility; and it assigns pride of place to
appearances. Anecdotes about Pyrrho's life (365/60-275/70
BC) convey how unaffected he was (DL 9.61-69). This kind of
ideal--a tranquil state of mind--is not part of Academic
skepticism, and scholars disagree on its role in Pyrrhonism
(Machuca 2006; Striker 2010; Perin 2020; on Democritean
influences on tranquility in Pyrrho and Timon, cf. Svavarsson 2013).
Insofar as the point of the anecdotes about Pyrrho's life is
that Pyrrho did not avoid or pursue anything with fervor, or that he
did not despair about things that other people find terrible, they
capture ideas that remain central to Pyrrhonism (for a general account
of early Pyrrhonism, cf. Castagnoli 2013; on Sextus' take
on Pyrrhonian tranquility, cf. Svavarsson 2015).



The biographical anecdotes portray Pyrrho as a strikingly
unconventional figure, unaffected not just by emotion and belief, but
also by perception--to the extent that friends had to pull him
off the street when a wagon approached (DL 9.62). At the same time,
Pyrrho seems to have said that the skeptic adheres to appearances
(*phainomena*) (DL 9.106; Bett 2000, 84-93; on earlier
notions of appearances relevant to skepticism, cf. Barney 1992). This
might suggest that he would not cross the street when a wagon is
approaching, and so appears to him. One story makes Pyrrho appear
not only unusual, but arguably a not so sympathetic character. Passing
by a drowning man, he was so unmoved that he simply walked on (DL
9.63). This is in rather stark contrast with Stoic notions of
unaffectedness, where the idea would be that, not being disturbed by
emotions like fear and panic, the passerby is ideally equipped to help
effectively. Some biographical details can seem to mold
Pyrrho's life to fit the schema of the sage: a traveler to the
East (Flintoff 1980), whose insights are conveyed in brief sayings; an
enigmatic figure, exemplary and shocking at the same time. Though it
is difficult to assess the testimony on Pyrrho's travels,
scholars increasingly explore resonances between Pyrrho's
pronouncements, later Pyrrhonian skepticism, and dimensions of
Buddhist philosophy (Hanner 2020). For example, Mill (2018) argues
that a tradition in classical Indian philosophy develops a
"skepticism about philosophy" that resembles dimensions of
Pyrrhonian thought.



Even though he discussed tranquility and adherence to appearances,
Pyrrho was arguably no Pyrrhonian skeptic (Bett 2000, 14-62).
That is, it is likely that he put forward a dogmatic position, in the
sense that he had positive philosophical views about the character of
reality. Pyrrho wrote nothing. Much of what we know about him is
preserved through the writings of Timon, his adherent
(325/20-235/30 BCE) (Burnyeat 1980b; Clayman 2009). The
most important piece of testimony is a passage reporting an account by
Timon:



> 
> It is necessary above all to consider our own knowledge; for if it is
> in our nature to know nothing, there is no need to inquire any further
> into other things. [...] Pyrrho of Elis was also a powerful
> advocate of such a position. He himself has left nothing in writing;
> his pupil Timon, however, says that the person who is to be happy must
> look to these three points: first, what are things like by nature?
> second, in what way ought we to be disposed towards them? and finally,
> what will be the result for those who are so disposed? He [Timon] says
> that he [Pyrrho] reveals that things are equally indifferent and
> unstable and indeterminate (*adiaphora kai astathmeta kai
> anepikrita*); for this reason, neither our perceptions nor our
> beliefs tell the truth or lie (*adoxastous kai aklineis kai
> akradantous*). For this reason, then, we should not trust them,
> but should be without opinions and without inclinations and without
> wavering, saying about each single thing that it no more is than is
> not, or both is and is not, or neither is nor is not (*ou mallon
> estin* *e ouk estin e kai esti kai ouk estin
> e oute estin oute ouk estin*). Timon says that the result
> for those who are so disposed will be first speechlessness
> (*aphasia*), but then freedom from worry (*ataraxia*);
> and Aenesidemus says pleasure. These, then, are the main points of
> what they say (Aristocles in Eusebius *PE* 14.18.1-5 =
> DC53; tr. Bett 2000 with changes)
> 



In response to the first question, how things are in their nature,
Pyrrho makes a metaphysical claim: they are indeterminate (Bett 2000,
14-29). There are no stable items, or no items with stable
properties. Scholars sometimes hesitate to ascribe such a position to
Pyrrho, because it is undoubtedly dogmatic. Perhaps the text can be
given an epistemological reading: things are indifferentiable and
unmeasurable and undecidable, because we fail in differentiating,
measuring, and determining how they are (Svavarsson 2010; Thorsrud
2010). But Pyrrho's response to the second question may only
follow if we adopt the metaphysical reading (Bett 2000, 29-37).
Pyrrho infers that our perceptions and beliefs are neither true nor
false. They are not truth-evaluable, presumably because there are no
facts which could be correctly captured. Third, if we understand these
things, speechlessness (*aphasia*) follows, and then
tranquility (*ataraxia*). Pyrrho does not say that we should
cease to speak. He suggests that we adopt a complicated mode of
speech, constructed around the expression *ou mallon*
("no more"), which aims to capture the indeterminate
natures of things, when we attempt to say anything about anything
(Bett 2000, 37-39; Vogt 2021).


### 4.2 Aenesidemus, the Ten Modes, and Appearances



Aenesidemus (first century BCE) was discontented with the views
discussed in the Academy at his time, of which he began as an
adherent. Philo's proto-externalism as well as a counterposition
formulated by Antiochus both appeared to him dogmatic. Aenesidemus
aimed to revive a more radical skepticism, and left the Academy for
this purpose. Arguably, he is the first Pyrrhonian skeptic.
Aenesidemus wrote a treatise, the *Pyrrhonian Discourses*,
probably similar in structure to Sextus' *Outlines of
Pyrrhonism* and partially preserved in a summary by Photius:
a general account of skepticism, followed by books on particular
philosophical questions (Hankinson 2010). The basic elements of
Aenesidemus' skepticism are: the skeptic puts appearances and
thoughts into opposition; this generates equipollence
(*isostheneia*, lit. "of equal weight") between
several appearances and/or thoughts; suspension of judgment follows;
with it comes tranquility; and the skeptic leads a life according to
appearances (DL 9.62, 78, 106-7). However, we do not know much
detail of his views on these matters. Instead, Aenesidemus is famous
for having developed Ten Modes or Tropes--forms of argument by
which the sceptic puts appearances and thoughts into opposition. Key
questions about Aenesidemus' skepticism concern (i) the
interpretation of his Modes, (ii) the relationship of his philosophy
to competing theories, (iii) the scope of the Ten Modes, and (iv) the
skeptic's mode of speech.



(i) Conflicting Appearances or Causal Invariance. The Ten Modes are
preserved in Diogenes Laertius (9.78-88), Philo of Alexandria
(*On Drunkenness* 169-202), and Sextus. Diogenes'
account of the Ten Modes may postdate Sextus' (Sedley
2015). Sextus gives extensive illustrations, and integrates the Ten
Modes into his general account of Pyrrhonism (*PH*
1.36-163; cf. *M* 7.345 for ascription of the Ten Modes
to Aenesidemus; cf. Annas-Barnes 1985 and Hankinson 1995, 268; the
sequence below follows Sextus). Here is the first of the Ten Modes,
interpreted in two ways.



> 
> 
> **10-1**:
>   
> 
> Arguments concerning oppositions based on the differences between
> kinds of animals.
> 
> 
> 
> **Conflicting Appearances Interpretation:**
>   
> 
> *X* appears *F* to animal of kind *A* (e.g.,
> humans) and *F*\* to animal of kind *B* [where *F*
> and *F*\* are opposite or otherwise incompatible properties]. We
> cannot judge how *X* really is, because we are a party to the
> dispute.
> 
> 
> 
> **Causal Invariance Interpretation:**
>   
> 
> For something to be 'really' *F*, it would have to
> consistently affect different perceivers as *F*. But different
> constitutions of different animals cause different impressions of the
> same thing. For different animals, something is *F* and
> *F*\* (where *F* and *F*\* are opposite or
> otherwise incompatible properties). Therefore, things do not seem to
> really be *F* or *F*\*.
> 
> 
> 



The Conflicting Appearances Interpretation is based on Sextus'
account (Annas-Barnes 1985). The focus here is on the idea that every
kind of animal, perceiver, sensory faculty, thinker, or judger
(depending on which mode we consider) is only one of several animals,
perceivers, sensory faculties, thinkers, or judgers. The object is
perceived or considered from a particular point of view. Everyone is a
party to the dispute, and there is no 'view from nowhere.'
Accordingly, the dispute cannot be decided. The Causal Invariance
Interpretation, on the other hand, suggests that the focus on
decidability is introduced by Sextus. Aenesidemus may (implicitly or
explicitly) have endorsed the following idea: if *X* were
*F* by nature, *X* would affect everyone as *F*.
If *X* affects different people (living beings, sensory
faculties, etc.) as *F* and *F*\*, *X* is by
nature neither *F* nor *F*\*. For example, if *X*
is harmful to *A* and beneficial to *B*, it is neither
harmful nor beneficial in its nature (Woodruff 2010, Bett 2000). The
Ten Modes can generally be construed as engaging either with conflicts
between appearances or with causal invariance:



> 
> 
> **10-2**:
>   
> 
> Arguments based on the differences among human beings (differences in
> body and in soul).
> 
> 
> 
> **10-3**:
>   
> 
> Arguments based on the differences between the senses and on the
> complexity of perceived objects.
> 
> 
> 
> **10-4**:
>   
> 
> Arguments based on states (dispositions and conditions of a human
> being, such as age, motion versus rest, emotions, etc.).
> 
> 
> 
> **10-5**:
>   
> 
> Arguments based on positions, distances, and places.
> 
> 
> 
> **10-6**:
>   
> 
> Arguments based on mixtures (objects in conjunction with external
> things like air and humidity; physical constituents of sense organs;
> physiology of thought).
> 
> 
> 
> **10-7**:
>   
> 
> Arguments based on the composition of the perceived object.
> 
> 
> 
> **10-8**:
>   
> 
> Arguments based on relativity (to the judging subject, to
> circumstances, etc.). 10-8 comprises at least 10-1 to 10-7, or all Ten
> Modes.
> 
> 
> 
> **10-9**:
>   
> 
> Arguments based on constancy or rarity of occurrence.
> 
> 
> 
> **10-10**:
>   
> 
> Arguments concerned with ways of life, customs, laws, mythical
> beliefs, and dogmatic assumptions, all of which can be put into
> opposition to each other.
> 
> 
> 



(ii) Skepticism, Relativism, Epicureanism. Consider first the
relationship between skepticism and relativism (cf. Bett 2000; Vogt
2012a, ch. 4). Relativism, as envisaged in Plato's
*Theaetetus*, looks at a similar range of phenomena. Things
appear different to different kinds of animals; to different people;
and so on. Relativism embraces the intuition that there is (as we
would say today) faultless disagreement. That is, you and I disagree,
but neither of us is wrong. Accordingly, metaphysical relativism
claims we must give up the intuition that we both refer to the same
thing. In the *Theaetetus*, the world dissolves into radical
flux: there are no stable items with stable properties that we both
refer to.



The Ten Modes, according to Conflicting Appearances, differ from
relativism by turning precisely the other way (Annas-Barnes 1985,
97-8; Pellegrin 1997, 552-3). They implicitly rely on the
intuition that there are stable items with stable properties. Of
course, the skeptic is not committed to the thesis that opposites
cannot hold of the same thing, and that therefore no two conflicting
appearances can be true. However, the modes presuppose a common sense
metaphysics that does not accommodate faultless disagreement. In all
cases of disagreement, at best one of us can be right. If we cannot
figure out which view is right, we should suspend. This does not mean
that Pyrrhonians are committed to a common-sense metaphysics. The Ten
Modes are only one of several tools that skeptics have at their
disposal. They may thus imply a metaphysics that, at other points,
skeptics would call into question (cf. Fine 2003b, 352).



Causal Invariance differs from Conflicting Appearances precisely with
respect to the metaphysics that is, even if only dialectically,
invoked. Aenesidemus seems to have explored the relationship between
skepticism and flux. He remarks that skepticism leads to Heraclitean
philosophy. The idea that one thing appears to have contrary
properties (the ones it appears to different animals/persons/senses to
have) leads to the idea that one thing actually has contrary
properties (*PH* 1.210; cf. Schofield 2007 on the role of
Heraclitus and causal invariance). This remark can be taken as an
expression both of moderate flux and of relativism (Aenesidemus does
not seem to think of radical flux, where it is no longer even possible
to refer to anything). There is no stable reality of how things are
(moderate flux); *X* is *F* and *F*\* insofar as,
if *X* seems *F* to *A*, this is true for
*A*, and *F*\* to *B*, this is true for *B*
(relativism). This proposal differs from the Causal Invariance
interpretation of the Modes presented above. There, Aenesidemus seems
to argue that things do not really have stable properties (they are
neither *F* nor *F*\* by nature); he does not say that
they are *F* and *F*\* (as relativism says).



A third approach, competing with skepticism and relativism, is
Epicurean epistemology. Again, the set of phenomena to be accounted
for is the same. But it is described differently. Epicurus insists
that we should not even speak of conflicting appearances. Rather, we
should speak of different perceptions. Perceptions cannot refute each
other, because they are of the same weight. Epicurus here uses the
term that is central to Pyrrhonism: equal weight,
*isostheneia* (DL 10.31-2). The fact that
perceptions differ has perfectly reasonable explanations: I look from
a distance, you look from nearby; I have a cold, you are healthy; I am
a human being, another cognizer is a dog; and so on. These facts
figure in the explanations of how our perceptions are constituted.
Accordingly, Epicurus argues, all perceptions, even though they
differ, are true. They all have a causal history that physics can
explain. The precise interpretation of this proposal is controversial.
One might object that the notion of truth employed here is deeply
puzzling. It is not clear what it means to describe all perceptions as
true if they cannot be true *or* false.



(iii) Scope. For the greatest part, the Ten Modes seem to be concerned
with perception in a broad sense, so that it includes pleasure and
pain, harm and benefit, as well as pursuit and avoidance. To perceive
something as pleasant or beneficial is to pursue it. Perception and
evaluation are also mixed in another way: depending on the frequency
with which we perceive something, it seems more or less amazing and
precious to us. **10-10** envisages oppositions that can
be construed with the help of dogmatic theses. The Ten Modes thus fit
Sextus' description of what skepticism is: the ability to put
appearances and thoughts (*phainomena* and *nooumena*)
into opposition (*PH* 1.8, 1.31-33; cf. DL 9.78).



Another issue concerning the scope of the Ten Modes is whether they
address general or particular matters. Compare the example of whether
the tower is round or square (T) to the example of whether honey is
sweet or bitter (H). (T) is a particular; the question is whether this
tower is round or square. (H) can be construed as a particular
("is this bit of honey sweet?"), or as a general issue
("is honey sweet?"). The Ten Modes offer strategies for
suspension of judgment on both kinds of questions.



Scholars have asked whether it is a problem for skepticism if the Ten
Modes appear 'systematic' (Sedley 2015). A set of
arguments that aims to be complete, covering domains according to a
standardized pattern, may appear to be out of tune with the
skeptic's presumed mode of investigation. Purportedly, skeptics
think through given questions as they arise, arriving at suspension of
judgment in a piecemeal fashion. If this self-description is to be
taken at face value, then modes of generating suspension of judgment
across the board may appear problematic. In this respect, Diogenes
Laertius' report of the Ten Modes may be superior to
Sextus' account. Diogenes begins with a remark that suggests
that skeptics pick up where other philosophers have already begun to
make an argument (9.78-9). Other philosophers have collected,
presumably, ways in which 'we are persuaded', say, because
things regularly appear the same way. Now the skeptics, as it were in
response to this, add a collection of further cases, where things do
not appear the same way to different cognizers. If this is the
dialectical set-up, the Ten Modes may not be 'systematic'
in ways that harm skepticism. They may co-opt the patterns of dogmatic
reports about cases where appearances are stable (Sedley 2015).



(iv) Language. Aenesidemus contributes an interesting move to the
question of how the skeptic can speak. Consider the relationship
between a skeptic's state of mind and their utterances. One way
to construe this relationship is that an utterance reflects a state of
mind. This is a background assumption to the idea that, if skeptics
use assertoric language, they hold beliefs. Another option is to
assume that language does not have the means to capture the
skeptic's state of mind. On this premise, a skeptic might flag
their utterances as falling short of doing so. This is
Aenesidemus' strategy. He says that the Pyrrhonian determines
nothing, and not even this fact that he determines nothing. The
Pyrrhonian puts matters in such terms, he says, because he has no way
to express the actual thought of the sceptic in determining nothing
(Photius, *Bibl*. 169b40-170a14, = 71C(6)-(8) LS).


### 4.3 Agrippa, and the Five Modes



Almost nothing is known about Agrippa (1st to
2nd century CE; SE *PH* 1.164-177; DL
9.88-89). However, the modes of argument that Sextus calls the
Five Modes are attributed to him. These modes are among the most
famous arguments of ancient skepticism (Barnes 1990, Hankinson
2010).



> 
> 
> **5-1 *Diaphonia***:
>   
> 
> The mode that argues from disagreement. With respect to some matter
> that presents itself, there is undecided (*anepikriton*)
> conflict, both among the views of ordinary life and the views held by
> philosophers. Due to this, we are unable to choose or reject one
> thing, and must fall back on suspension.
> 
> 
> 
> **5-2 *Eis apeiron ekballonta***:
>   
> 
> Arguments that throw one into an infinite *regress*. That which
> is brought forward to make a given matter credible needs yet something
> else to make *it* credible, and so on *ad infinitum*.
> Since we thus have no starting point for our argument, suspension of
> judgment follows.
> 
> 
> 
> **5-3 *Pros ti***:
>   
> 
> Arguments from *relativity*. *X* only ever appears
> such-and-such in relation to the subject judging and to the things
> observed together with it. Suspension on how *X* really is
> follows.
> 
> 
> 
> **5-4 *Hypothesis***:
>   
> 
> Someone makes an assumption without providing argument. A dogmatist,
> if thrown back into an infinite regress of arguments, just assumes
> something as a starting-point, without providing an argument
> (*anapodeiktos*). We suspend over mere
> hypotheses--they could be false, opposite hypotheses could be
> formulated, and so on.
> 
> 
> 
> **5-5 *Ton diallelon***:
>   
> 
> Arguments that disclose a *circularity*. This mode is used when
> that which ought to confirm a given investigated matter requires
> confirmation (*pistis*--credibility) from that matter. We
> are unable to assume either in order to establish the other. We
> suspend judgment on both.
> 
> 
> 



It is a commonplace to say that, while the Ten Modes, as presented in
Sextus, are concerned with conflicting appearances, the Five Modes are
about argument or proof. In these modes, the skeptics develop
strategies by which to attack theories that the dogmatists defend. If
this is how we characterize the Modes, Aristotle's objection
(section 2.3) immediately comes to mind. Do the Five Modes reveal the
skeptic's lack of understanding because they presuppose that
everything is subject to proof? (Barnes 1990; Hankinson 1995,
182-92; Long 2006, ch.3) The three so-called formal
modes--Regress, Hypothesis, and Circularity--can be
construed in this fashion: when employing them, the skeptic can argue
that every premise must be supported by argument; if it is not so
supported, the theory begins from a mere hypothesis (on earlier uses
of the term *hupothesis* in Plato and in medicine, cf. Cooper
2002 [2004a]); or it is ultimately circular.



However, the skeptic might not be vulnerable to this objection. First,
the Five Modes can be construed as dialectical, invoking dogmatic
theories of justification (Striker 2004). Second, they might be
broader in scope. **5-1** and **5-3**
explore disagreement and relativity. Skeptical examination often
begins with the Mode of Disagreement: different answers to a given
question are surveyed, and the conflict between them is observed. The
interpretation of **5-1** hangs, for the most part, on
the question of whether *anepikriton* should be translated as
'undecided' or 'undecidable' (Barnes 1990). It
would be dogmatic to claim that matters are undecidable. The
Pyrrhonist must prefer the idea that, up to now, matters have not been
decided. In applying the Mode of Disagreement, skeptics can
either record a conflicting argument that others have formulated or
come up with an argument that disagrees with a view formulated by a
dogmatist (cf. Sienkiewicz 2019, 47-51). This leads to the question of
whether something can be found that would decide matters, and thus to
the application of further modes. Scholars have observed that
**5-3**, the Mode of Relativity, does not really fit into
the Five Modes. However, the Five Modes could be designed to supersede
and include the Ten Modes, and **5-3** might be viewed as
capturing the common thread of the Ten Modes. With the help of
**5-3**, the skeptic can argue that the premises that
theorists employ are formulated from particular points of view, in
particular contexts, and so on (for a reading that emphasizes the role
of the first mode at the expense of the role of the third, cf.
Sienkiewicz 2019).



Third, even the so-called formal modes (**5-2**,
**5-4**, **5-5**) might not be narrowly
concerned with proof, but rather with everything that can lend
credibility to something else. Consider Regress
(**5-2**), the first of the formal modes. The text does
not actually speak of proof (*apodeixis*) (this is obscured by
Bury's Loeb translation; **5-4** is the only place
in Sextus' report of the Five Modes that uses a cognate of
*apodeixis*). Sextus' language is wider: the mode deals
with everything that can make something else credible. We might read
this in the context of the Hellenistic view that proof is a species of
sign (*PH* 2.122). A sign reveals something non-evident. Smoke
that reveals fire has, from this point of view, a function and
structure that is similar to a proof. The target of the Five Modes
might be sign-inferences in general. If this is so, then their target
might include what we would call inductive reasoning and causal
explanations (when Sextus introduces a further set of modes, the
Causal Modes, he says that they are not really needed, because the
relevant work can be done by the Five Modes; *PH*
1.180-86). Taken together, the Five Modes deny all "proof,
criterion, sign, cause, movement, learning, coming into being, and
that there is anything by nature good or bad." (DL 9.90). This
is notably more than just proof. Indeed, it is an excellent summary of
the key topics in Sextus' discussions of logic, physics, and
ethics.


### 4.4 Sextus Empiricus



Sextus' (ca. 160-210 CE) epithet, Empiricus, indicates
that he belonged to the empiricists, a medical school (cf.
Svavarson 2014 for a brief conspectus of Sextus' philosophy).
The empiricist medical school argued against rationalistic tendencies
in medicine (Frede 1990; Allen 2010). Rationalism in medicine aims to
give causal explanations as a basis for therapies. Empiricism, on the
contrary, confines itself to observation and memory. Somewhat
confusingly (considering his name), Sextus discusses differences
between Pyrrhonism and empiricism, and says that skepticism is closer
to medical methodism than to empiricism (Allen 2010). On the whole, it
may be safest to think of Sextus as rejecting medical rationalism as
well as other trends within medicine that by Sextus' lights are
dogmatic. Methodism follows appearances, and derives from them what
seems beneficial. No explanations are attempted, no underlying
substances postulated, and no regularities assumed--these are
some of the rationalistic methods that both methodism and empiricism
argue against. Methodism also makes no statements to the effect that
such explanations cannot be given, or that underlying substances and
regularities do not exist, as Sextus says empiricism does (SE
*PH* 1.236-241). Beyond the fact that Sextus was a
doctor and wrote on medicine (M 7.202, M 1.61), his philosophical
thinking seems shaped by engagement with medical writers. Scholars
have long been interested in the relationship between medicine and
skeptical arguments that pertain to be therapeutic (Voelke 1990). More
recently, scholars explore ways in which medical writings, in
particular by Galen, inform Sextus' thinking, even on specific
issues such as how to conceive of and solve sophisms (Schmitt,
forthcoming). It has also been argued that the skeptics'
application of the modes should be interpreted in light of the
methodological commitments of non-rationalist medicine (Sienkiewicz
2019, 2021).



Sextus' philosophical writings are traditionally divided into
two groups. The *Outlines of Pyrrhonism* [*PH*] consists
of three books. *PH* 1 is the only general account of
Pyrrhonism that survives. *PH* 2 and 3 discuss questions of
logic, physics, and ethics. The other writings are summarily referred
to, traditionally, as *Against the Mathematicians*
[*M*]. In fact, they oppose not just mathematical, but also
other theorists: the title really means *Against the
Theoreticians*, or *Against the Learned* (Bett 2012). In a
sense, only *M* 1-6 should go by that title. It is a
complete work, and *M* 7 does not seem to be its continuation
(Bett 2012, "Introduction"). *M* 1-6 discuss
grammar, rhetoric, geometry, arithmetic, astrology, and music theory.
They argue against theoretical 'learning' in these fields.
*M* 7-11 discuss core questions of the three
philosophical disciplines, logic, physics, and ethics, and could
plausibly be referred to as *Against the Logicians* (*M*
7-8), *Against the Physicists* (*M* 9-10),
and *Against the Ethicists* (*M* 11). Scholars disagree
on whether *M* is earlier (Bett 1997) or later than *PH*
(Janacek 1948 and 1972). Scholars also disagree on whether we can
evaluate different strands of skepticism within Sextus as more or less
sophisticated. Those who consider *PH* as later often do so
because they think it shows greater philosophical sophistication,
either by avoiding claims that a certain matter cannot be known
(sometimes described as negative dogmatism), as found in *M*
1-6 and *M* 11, or by streamlining discussions from
*M* 7-10 (Bett 1997; Brunschwig 1980).



These questions are complicated further by Sextus' attempt to
incorporate diverse material, such as different sets of Modes, into
his skepticism. According to recent interpretations, the
different sets of modes are part of an integrated philosophical
approach (Powers 2010). Morison (2018) argues that the Ten Modes and
Five Modes both serve the same purpose: to produce equal and opposing
arguments to arguments in support of philosophical or scientific
views. Arguably, two kinds of consistency are at work in Sextus'
writings. On the one hand, Sextus aims at the consistency of one
philosophical outlook. On the other hand, he aims at the consistency
of having a response to every objection. These two aims overlap
greatly, but they can also come apart. A given argument might refute a
particular critic. This argument may go back to various earlier
versions of Pyrrhonism. Similarly, the critical objection that is
refuted may be traced to dogmatic theories formulated over the course
of several centuries. As a result, a given argument in Sextus may be
effective against a given objection he has in mind. It may thus
preserve consistency in the sense of leaving the skeptic unharmed by
dogmatic criticism. But at the same time, this argument may have
implications that are in tension with the way in which Sextus explains
skepticism in other passages. Such tensions are particularly important
with respect to the way in which Sextus uses core concepts. For
example, it is not clear that Sextus uses the notion of appearances
(*phainomena*) in a consistent fashion (*PH*
1.8-9; 1.15; 1.22; for the view that Sextus employs the notion
consistently throughout, see Barney 1992). At times, he draws on the
contrast between appearances and thoughts (*noumena*). But for
the most part, the term refers to all cases where something seems
so-and-so to the skeptic, either perceptually or in thought. In some
contexts, Sextus draws on the idea that appearances are impressions,
invoking the dogmatic assumption that impressions are passive. In
other contexts, he does not envisage appearances as entirely passively
experienced (Vogt 2012b).



It is thus no surprise that the interpretation of Sextus'
Pyrrhonism is quite controversial. This applies in particular to the
question of whether the skeptic has any beliefs, or beliefs of any
kind. In the past 40 years, scholars have paid attention to this
question more than to any other interpretive issue. Insofar as the
texts may contain different strands of Pyrrhonian argument, exegesis
is to some extent shaped by the philosophical interests we bring to
the texts. Two ideas are particularly prominent here. First, some
scholars find in Sextus an account of action that challenges standard
ancient and modern theories of agency. These theories might portray
ordinary agents as all-too-rational, as if every action involved an
actively formed belief that such-and-such is good. Scholars explore
how far we can draw on Sextus, asking whether a life guided by
appearances (as Sextus says the skeptic's life is) might after
all be rather ordinary (Frede 1979 [1997]). Second, one might on the
other hand embrace those aspects of Sextus' texts that make
Pyrrhonism look radically different from ordinary life. From this
perspective, Sextus' writings invite reflection on the question
of whether it would be possible to live without belief (Burnyeat 1980
[1997]; Barnes 1982 [1997]; Burnyeat 1984 [1997]).



*PH* 1, which figures most prominently in scholarly
discussions, is a *tour de force*. Sextus gives a general
account of what skepticism is, including skeptical investigation,
suspension of judgment, the skeptic's end, action, and language;
he gives lists and illustrations of various sets of Modes; he explains
the so-called skeptical formulae (*phonai*), such as
"I determine nothing," "non-assertion,"
"maybe," and so on; and he compares skepticism to
relevantly similar philosophies.



Sextus emphasizes that the skeptic is an investigator. Others either
arrive at theories (dogmatism) or at claims about inapprehensibility
(negative dogmatism--that the matter investigated is beyond
one's capacity to decide, and so is unknowable). But the skeptic
continues to investigate (*PH* 1.1-4). Investigation is
described as setting appearances and thoughts into opposition
(*PH* 1.8) (Morison 2011 offers a reconstruction of skepticism
that takes its starting-point from this description), and as the
application of the various sets of Modes (*PH* 1.36-186).
Skepticism does not have teachings, but it is an approach in
philosophy (Smith 2022). Many of the thoughts the skeptics arrive at
are expressed in the skeptical formulae (*PH* 1.13-15;
187-209). The starting-point (*arche*) of
skepticism is divergency--*anomalia*. The
proto-skeptics are disturbed by the discrepancies they encounter, and
begin to investigate (PH 1.12). They hope to gain quietude by settling
what is true and what is false. But then they have a surprising
experience. Encountering disagreement where several views appear to be
of equal weight (*isostheneia*), they find themselves unable to
decide things, give up, and experience tranquility (*ataraxia*)
(Striker 1990 [1996]; Nussbaum 1994). The skeptic's end
(*telos*) is tranquility in matters of belief (*kata
doxan*) and moderate affection (*metriopatheia*) in matters
that are forced upon us (*PH* 1.25-29). That is, skeptics
can free themselves from those kinds of turmoil that come with holding
beliefs. They cannot free themselves from freezing, thirst, or pain.
But they suffer less than others, for they do not add the belief
(*prosdoxazein*) that, for example, pain is bad. The skeptic
must explain how, without belief (*adoxastos*), they can
be active. Sextus says that skeptics follow appearances, and that is,
that they adhere to the fourfold ways of life (*PH*
1.21-24). Nature supplies them with perception and thought;
necessary affections compel them (for example, thirst guides them to
drink); they go along with traditions and customs; and they can do
technical things by having been instructed in skills. The notion of
appearances is also central to Sextus' account of how the
skeptic can speak. Without making assertions, a skeptic reports
(*apangellein*) like a chronicler (*historikos*)
what appears to them now (*PH* 1.4).



I shall discuss the following aspects of Sextus' skepticism: (i)
investigation and tranquility, (ii) concepts and inference rules,
(iii) belief, (iv) the formulae, (v) appearances, (vi) language, (vii)
action, and (viii) the so-called special arguments (that is, arguments
that do not explain the nature of Pyrrhonism, but engage with specific
dogmatic theories in logic, physics, and ethics).



(i) Investigation and tranquility. Investigation must aim at discovery
of the truth, otherwise it is not genuine investigation. However, a
skeptic seems to mechanically apply the skeptical Modes, in order to
generate suspension of judgment and tranquility. Scholars disagree on
whether the skeptics genuinely aim at the truth (Palmer 2000;
Striker 2001; Perin 2006; Veres 2020b), while they (also) aim at
tranquility. Note that this objection, unlike the other problems
central to contemporary engagement with ancient skepticism, was not
raised in antiquity. If ancient skepticism is approached in the
context of the larger study of ancient philosophy, we might first of
all note that the skeptics in a sense agree with Socrates, Plato,
Aristotle, Epicurus, and the Stoics. All these philosophers defend, in
so many formulations, a life of reason, of contemplation, of wisdom,
or of inquiry as the best or at least a very good human life (on
affinities between the skeptics' commitment to inquiry and
Aristotle, cf. Olfert 2015). The objection that skeptical inquiry
seems insincere, then, may not have come up in antiquity in quite the
way in which it is discussed today because a commitment to inquiry
would be common ground among most philosophers. Further, we might
observe that aiming at the truth includes two aims: to accept truths,
and to avoid falsehoods. The Modes are tailored to keep us from
assenting to something that could be false. Insofar as the
skeptic's effort to avoid falsehoods expresses a valuation for
the truth, the skeptic might be a genuine investigator (Vogt 2012a,
ch. 5; Olfert 2014).



A related objection calls into question the actual practice of
skeptical inquiry. Does Sextus rely on the assumption that, in any
given case of putting several arguments into opposition, these
arguments are equally persuasive for the skeptic? This seems
unrealistic: at least in some cases, skeptical inquirers are bound to
be more strongly attracted to one view than to another. How then do
they arrive at suspension of judgment? One skeptical strategy is to
remind oneself that additional arguments will be formulated in the
future (*PH* 1.33-34, 89, 96-97; 2.38-41;
3.233-34). Another strategy is to consider that different
arguments are persuasive to different people (Svararsson 2014).
Relatedly, skeptics may find themselves in a position comparable to a
student who takes a seminar on freedom and determinism: it is possible
to be more attracted to one view rather than another, and at the same
time be aware that as far as the arguments are concerned, there is
unresolved disagreement among several views, to the effect that
neither of the views seems compelling in ways that warrant assent (cf.
Vogt 2012a, ch. 5, on how the skeptical expression "as far as
the argument is concerned" bears on this question; for general
discussion of this expression, cf. Brunschwig 1990).



(ii) Concepts and rules of inference. If skeptics do not assent, then
how can they understand the terms philosophers use (*M*
8.337-332a)? Even more radically, how can they even think
(*PH* 2.1-12)? This objection, which Sextus says is
continually raised against the skeptics, proceeds on the assumption
that possession of concepts involves the acceptance of assumptions.
For example, in order to examine a given theory of proof, the skeptic
must have a notion of what proofs are. This involves assumptions: for
example, the assumption that a proof contains premises and a
conclusion. Sextus' response to this objection invokes the
Epicurean and Stoic theories of preconceptions. Human beings are not
born with reason (Frede 1994, 1996). The acquisition of reason is a
nature-guided process of concept acquisition. At a given age, children
have completed this process. They have become rational, which means
that they can perceive and think in a conceptual way. Only now, they
have rational impressions to which they can assent. The acquisition of
preconceptions did not involve assent, simply because the child was
not yet rational (Brittain 2005).



Sextus invokes dogmatic ideas about the acquisition of reason (or: the
abilities of conceptual thought) in his response to the Apraxia Charge
(*PH* 1.23-4). Skeptics are, first of all, active because
nature has equipped them with perception and thought (Vogt 1998,
2010). More generally, the skeptics' ability to think and
investigate depends on the fact that they have acquired concepts as
part of growing up. This process did not involve assent, and
accordingly, Sextus argues that the skeptic's ability to think
does not violate suspension of judgment (cf. Brunschwig 1988; Vogt
2012a ch. 6; Grgic 2008; Fine 2011). It is conceivable, though, that
the skeptic's ability to understand involves some knowledge,
namely a kind of knowledge that does not entail any belief (Corti
2009, part III; Corti 2015). This option appears counterintuitive
given today's premises in epistemology, according to which
someone who knows that p also believes that p. The relevant notion of
belief in skeptical discussions, *doxa*, as well as the
relevant ancient notions of knowledge, however, may behave quite
differently (cf. Vogt 2012a and Moss and Schwab 2019 on belief;
Burnyeat 1980c, Frede 2008 and Schwab 2016 on knowledge). Insofar as
*doxa* is an inherently deficient activity and attitude, and
insofar as knowledge is conceived in elevated ways, knowledge without
belief is a rather intuitive option within ancient epistemology. If
understanding concepts and arguments involves knowledge that does not
entail beliefs, the skeptics may be taken to have such knowledge.
Modern critics raise the further question of whether the skeptic must
endorse logical laws (such as the Principle of Non-Contradiction) and
rules of inference. In particular, they ask whether a skeptic is
committed to the logical validity of the conditionals they formulate
when arguing against the dogmatists (Sorensen 2004). Sextus records no
ancient version of this complaint, and accordingly no direct
response. Relatedly, one may ask whether Sextus' method, in
particular regarding the Five Modes, is systematic in a way that is in
tension with suspension of judgment (cf. Sienkiewicz 2021, who defends
Sextus against this charge).



(iii) Belief. Bury, in his Loeb translation, translates
*adoxastos* as "undogmatically," for example,
when Sextus speaks (*PH* 1.15) of skeptics as saying that
"nothing is true." This translation suggests that Sextus
bans dogmatism from the skeptic's life, where this still leaves
room for other, non-dogmatic beliefs. But *adoxastos*
means non-doxastically or 'without belief' (cf. Burnyeat
1980 [1997]). As noted above, the skeptic's end is tranquility
in matters relating to belief--*kata doxan*. A skeptic
lives *adoxastos*. And even more confusingly, the
skeptics assent *adoxastos*, when they act.



Contemporary interest in Pyrrhonian skepticism was much spurred by
Michael Frede's paper "The Sceptic's Beliefs"
(1979 [1997]). Frede argues that ancient skepticism was traditionally
dismissed too easily as vulnerable to the Apraxia Charge, the charge
that, without belief, the skeptic cannot act. The skeptics seem to be
confident that they have replies to this objection. Thus, it seems
uncharitable not to look closely at these replies. Further, insofar as
these replies respond to the charge that without belief one cannot
act, we should focus on what the skeptics say about the role of belief
in their lives. Frede cites *PH* 1.13, and claims that in this
passage we find a distinction between two kinds of belief:



> 
> When we say that the skeptic does not dogmatize, we are not using
> 'dogma' in the more general sense in which some say it is
> dogma to accept anything (for the skeptic does assent to the
> experiences forced upon him in virtue of this-or-that impression: for
> example, he would not say, when warmed or cooled, 'I seem not to
> be warmed or cooled'). Rather, when we say he does not
> dogmatize, we mean 'dogma' in the sense in which some say
> that dogma is assent to any of the non-evident matters investigated by
> the sciences. For the Pyrrhonist assents to nothing that is
> non-evident. (*PH* 1.13; trans. Burnyeat (1984) [1997] with
> changes)
> 



Following Frede, several scholars focus on *PH* 1.13 when
discussing skeptical belief (with the notable exceptions of Barnes
1980 [1997] and Barney 1992). They take it to be obvious that, in this
paragraph, Sextus distinguishes between two kinds of belief, one which
he bans from the skeptic's life, and one which he allows into
the skeptic's life. Barnes (1982 [1997]) employs a distinction
between rustic and urbane skepticism. The rustic skeptic suspends on
all matters. The urbane skeptic suspends on scientific matters, but
holds ordinary beliefs. The clause "non-evident matters
investigated in the sciences" in *PH* 1.13 might be taken
as a point of reference for the urbane interpretation. However, Barnes
points out that this cannot be right. Everything can be considered as
a non-evident matter, even such things as whether honey is sweet.



Against Barnes, Frede argues that the relevant distinction must be
drawn between two kinds of assent, such that "having a view
involves one kind of assent, whereas taking a position, or making a
claim, involves another kind of assent, namely the kind of assent the
sceptic will withhold" (1984 [1997], 128). Sextus characterizes
skeptical assent in three ways. He speaks of forced assent (PH
1.23-24), involuntary assent (PH 1.19), and
*adoxastos* assent (PH 2.102). Frede does not explore the
details of how Sextus uses these notions. The core of his proposal is
that Sextus allows for a kind of assent that does not involve a claim
as to how things are in actual fact.



In (1979 [1997]), Frede is predominantly concerned with the
skeptic's reply to the Apraxia Charge. In (1984 [1997]) his
focus is on skeptical pronouncements such as "nothing can be
known." His distinction between two kinds of assent, and
accordingly two kinds of belief, is explored with respect to such
sentences. Frede writes that "[t]o be left with the impression
or thought that p [...] does not involve the further thought that
it is true that p" (133). This is the sense in which, on his
interpretation, the skeptic might think "nothing is
known." The thought counts as a belief, but not as a claim that,
in actual fact, nothing is known by anybody. Contrary to Frede's
interpretation, one might argue that to believe simply is to hold
true, at least according to the notions of belief that the skeptics
invoke in discussions with their contemporary critics (Vogt 2012b). It
is thus not clear that Frede's distinction is genuinely one
between two kinds of beliefs (Burnyeat 1980 [1997]). Perhaps it is a
distinction between two different propositional attitudes, only one of
which is belief. As Striker (2001) points out, there is a danger that
debates over this issue become merely terminological. We might thus
draw a distinction between two issues. It is one thing to disagree
with Frede on what should or should not be called belief, and another
to dispute whether he identifies and characterizes a phenomenon in the
skeptic's mental life. As Frede argues, skeptics find themselves
with a rather persistent thought, without having accepted it as true
in actual fact. This appears to capture a core element of skepticism:
the way in which the skeptic thinks such thoughts as "everything
is inapprehensible."



(iv) The Skeptical Formulae. *PH* 1.13, the passage in which
scholars find a distinction between two kinds of belief, occurs in a
chapter entitled "Does the Skeptic dogmatize?" One angle
from which we might disagree with Frede is to insist that *PH*
1.13 addresses the status of the core thoughts of skeptical
philosophy, rather than the question of skeptical belief. Consider the
rest of the chapter:



> 
> Not even in uttering the skeptical formulae about unclear
> matters--for example, "In no way more," or "I
> determine nothing," or one of the other formulae which we shall
> later discuss--do they dogmatize (*dogmatizein*). For if
> you dogmatize, then you posit as real the things that you are said to
> dogmatize about; but skeptics posit these formulae not as necessarily
> being real. For they suppose that, just as the formula
> "Everything is false" says that it too, along with
> everything else, is false (and similarly for "Nothing is
> true"), so also "In no way more" says that it too,
> along with everything else, is no more so than not so, and hence
> cancels itself along with everything else. And we say the same of the
> other skeptical formulae. Thus, if people who dogmatize posit as real
> the things they dogmatize about, while skeptics utter their own
> phrases in such a way that they are implicitly cancelled by
> themselves, then they cannot be said to dogmatize in uttering them.
> But the main point is this: in uttering these formulae they say what
> appears to themselves and report their own feelings without any belief
> *(adoxastos*), affirming nothing about external objects.
> (*PH* 1.14-15; trans. Annas-Barnes with changes)
> 



When explaining in *PH* 1.13 how the skeptic does not
dogmatize, Sextus may have a particular issue in mind: that some
skeptical formulae look like doctrines, and have traditionally been
turned against themselves due to their dogmatic surface-structure. For
example, "all things are indeterminate" looks like a
straightforward dogmatic statement. There is a long history of
skeptical attempts to explain the nature of such pronouncements so
that they no longer undermine themselves. Sextus arguably mentions
several solutions to this problem (*PH* 1.13-15 and
1.187-209; cf. Pellegrin 2010). In *PH* 1.15, Sextus
identifies the following as his main point: the skeptic merely reports
what appears to them. Along these lines, Sextus calls indeterminacy an
affection of thought (*pathos dianoias*; *PH* 1.198), a
state that the utterance "all things are indeterminate"
aims to capture. The other solution mentioned in *PH*
1.14-15 is somewhat more problematic: the skeptical formulae
cancel themselves out. That is, one can say them and convey something
through them. But then, once one has made a point, they as it were
turn back upon themselves and eat themselves up--as fire first
burns combustible materials and then destroys itself. This idea became
famous through another comparison Sextus uses (invoked by Wittgenstein
1922, 6.54): the skeptical pronouncements are like a ladder that
one climbs up; once one is on top, one can throw the ladder away
(*M* 8.481). Scholars disagree on whether Sextus in some sense
admits that these statements are self-refuting (McPherran 1987), or
whether he defuses their self-refutational structure (Castagnoli 2010,
III.14).



(v) Appearances (*phainomena*). While it is difficult to
establish a clear distinction between two kinds of belief in Sextus,
there is a comparatively more explicit distinction between two ways of
engaging with appearances. Sextus says that, while things
appear *X* to the skeptic, the skeptic does not affirm that
they are *X*. Questions that are traditionally discussed in
terms of whether the skeptic has beliefs thus might be addressed in
terms of whether the way things appear to the skeptic has a
judgment-component. Arguably, "*A* appears *X* to
me now" can be construed in different ways. Certain examples
(say, the way in which it makes sense to say both that the moon
appears small and that it appears large) may suggest that appearance
can but need not involve something like a judgment (Barney 1992). Some
formulations in Sextus seem to insist on a significant difference
between the mental activity of something appearing to a cognizer on
the one hand, and on the other hand the mental activity that, on the
level of language, is represented by assertion. This suggests that,
for Sextus, *A* appearing *F* to me now does not entail
that I hold it to be true that *A* is *F* (Vogt
2012b).



(vi) Language. Another approach to the question of whether the skeptic
has beliefs looks at skeptical language. Sextus insists that the
skeptic does not accept or reject any impression, and associates the
absence of these mental acts with the fact that the skeptic does not
affirm or deny anything (e.g., *PH* 1.4, 7, 10). Arguably, we
can infer from Sextus' account of the skeptic's utterances
what Sextus wants to say about the skeptic's mental states and
acts. That is, the question of language immediately bears on the
question of belief. The report on Pyrrhonian skepticism in Diogenes
Laertius is particularly instructive in this respect. Contrary to
scholarly focus on belief in reconstructing skepticism, it barely
mentions belief. Discussion of the skeptics' attitudes is almost
entirely conducted in terms of skeptical language and the skeptical
formulae (for detailed discussion of the relevant paragraphs, DL
9.74-7, cf. Corti 2015). If Sextus is read in light of the
report in DL IX, *PH* 1.13 may appear to be more of an isolated
passage than scholarly debates imply. Sextus too devotes much space to
accounts of skeptical expressions and language. It may thus be asked
whether scholars should reframe discussions, and pay more attention to
skeptical language then they previously have. As of now, there is one
monograph on skeptical language, Corti (2009), and one approach to
belief that focuses on language, Vogt (1998). Both scholars pursue
further ideas put forward by Barnes (1982 [1997]), who compares the
skeptic's utterances to avowals. The skeptic lays open their
state of mind, they announce or record (*apangellein*) it (Fine
2003a). In order to do this, the skeptic must misuse language
(Burnyeat 1984 [1997]). Some strategies to avoid assertion are given
in the context of the skeptical formulae ("non-assertion,"
"I determine nothing," and so on). (i) Skeptical
expressions can be used as signs, which reveal a state of mind
(*PH* 1.187). (ii) Expressions like "*ou
mallon*" (no more) and "*ouden mallon*"
(nowise more) can be used indifferently (in the sense of
interchangeably) (*PH* 1.188). (iii) As is the practice in
ordinary language, the skeptic can use expressions elliptically; for
example "no more" for "no more this-than-that"
(*PH* 1.188). (iv) People often use questions instead of
assertions and the other way around. Similarly, "no more"
can be construed as a question: "Why more this-than-that?"
(v) The skeptic misuses language and uses it in a loose way
(*PH* 1.191).



In *M* 1 and *M* 2, Sextus says that the skeptic goes
along with ordinary ways of using language (M 1.172, 193, 206, 218,
229, 233; M 2.52-3, 58-9). This seems to be a key resource
in construing skeptical ways of speaking: the skeptic exploits the
ways in which ordinary speakers can diverge from grammatically correct
speech, and still be understood. Apart from using their skeptical
formulae, and apart from conducting philosophical investigations,
which they can do in a dialectical mode, referring to theses,
arguments, and inferences, the skeptic also has to talk in everyday
contexts. It is here where we see best how skeptical utterances are
tailored to reveal a state of mind in which nothing is accepted or
rejected. Sextus takes great pains to construe his examples of
skeptical utterances according to the following schema:
"*X* appears *F* to me now." This will
generally be understood as an elliptical version of "*X*
appears *to be* *F* to me now." However, Sextus
consistently avoids "to be" (Vogt 1998; for the view that
"*X* appears F" avoids reference to external
objects, see Everson 1991). The peculiar form of skeptical utterances
suggests that Sextus sees a relevant difference between
"*X* appears to be *F* to me now" and
"*X* appears *F* to me now." The former
might imply reference to a state of affairs, and an epistemic usage of
"to appear" that could be rendered as "It appears to
me, that p," or, "I take it that p." This, however,
would be assertoric: the skeptic would state that it appears to them
that such-and-such is the case. But the skeptic's elliptical
utterances about what appears to them aim to be purely
phenomenological. They aim to report a condition of the
skeptic's mind, without expressing a judgment of any kind
(Burnyeat 1984 [1997]; Annas-Barnes 1985, 23-4; for an
assessment of these strategies in terms of modern philosophy of
language, cf. Pagin 2020). As part of the skeptics' way of life,
language can also be seen as an activity. That is, how the skeptics
can speak can be considered a sub-question of how the skeptics
can act. Skeptical utterances have been compared to Wittgensteinian
confessions, arguably a kind of speech act that is consistent with the
skeptics' avoidance of belief (Corti 2009, Parts I and II).
Moreover, the skeptics not only speak. They presumably also understand
what others say. A persuasive account of skeptical language must
explain both speaking and understanding (Corti 2009, Part III).



(vii) Action. Sextus says that appearances (*phainomena*) are
the practical criterion of the skeptic (*PH* 1.23-24). By
adhering to appearances, the skeptic is prevented from inactivity
(*anenergesia*). Note that Sextus does not describe the
skeptic as performing actions in the sense of dogmatic theory of
action, which involves belief and choice (cf. *M*
11.162-166). Contrary to the Academic skeptic, a Sextan skeptic
does not view themselves as a rational agent, who chooses one course
of action over another. Sextus claims an active life for the skeptic,
but not the life of a rational agent, as conceived by dogmatic
philosophers (Vogt 2010; Schwab 2020). This attitude has been
critically discussed for a long time, for example, with respect to its
ethical (Bett 2019) and political upshots (Marchand 2015) and with
respect to the skeptics' relation to the law (Marchand
2021).



The skeptic's forced assent is situated in the domain of action
(*PH* 1.13, 19, 29-30, 193, 237-8). Thirst, for
example, necessitates assent, and that means, it moves the skeptic to
drink. This kind of assent may be genuinely unrelated to
belief-formation of any kind. Rather, forced assent generates the
movement of action. But what about more complex kinds of activities,
such as applying a medication, or attending a festival? Sextus argues
that the skeptic adheres to custom, convention, and tradition, and to
what they have been trained to do. In explaining how adherence to
appearances in these domains generates activity, Sextus does not
mention assent. However, he might have to concede that, like drinking
when thirsty, more complex actions also involve some kind of assent.
In *PH* 2.102, Sextus says that the sceptic assents
non-doxastically (*adoxastos*) to the things relied on in
ordinary life. In *PH* 1.19, he mentions involuntary assent.
Accordingly, non-doxastic and involuntary assent may figure in those
domains of skeptical action that do not involve necessitation by
bodily affections. Non-doxastic assent is, from the point of view of
the Stoics, a contradiction in terms, just like forced and involuntary
assent. Assent is defined as in our power, and as that by which
beliefs are formed. If Sextus intends skeptical assent to be genuinely
non-doxastic and involuntary, then it does not have the core features
of assent as defined by the dogmatists.



(viii) Logic, Physics, Ethics, and the "disciplines." The
special arguments of the skeptic are directed against particular
theories in the three disciplines of Hellenistic philosophy: logic,
physics, and ethics. In addition, they address the so-called
disciplines, namely grammar, rhetoric, geometry, arithmetic,
astrology, and music-theory. Sextus' treatments of logic divide
up into two main topics: sign and criterion (cf. Bett 2005 on signs).
This structure reflects central concerns of Hellenistic epistemology
as well as of ancient skepticism. Skepticism looks for a
'decider' between conflicting appearances and thoughts. A
decider could be something evident. Dogmatic philosophers associate
the evident with the criterion of truth. For something to serve the
role of criterion, it cannot be equally disputed as the matters it
helps to decide. Or something non-evident could take on the role of
decider. For that to be the case, the skeptics argue, it would have to
be conclusively revealed by a sign or proof. If there is no compelling
theory of the criterion and no compelling account of sign and proof,
then there is nothing that can decide between several conflicting
views. Sextus' treatises on logic thus are not simply a
collection of individual arguments against various dogmatic theories.
Their main line of thought sketches a route into
skepticism. Along these lines, Vlasits (2020b) argues that
Sextus' treatment of logic in PH 2 is unified. Sextus'
argument is structured such as to lead to suspension of judgment on
the methodologies of the dogmatists. The final section of M 8 (463-81)
formulates a challenge for the skeptic that scholars interested in
self-refutational arguments have examined (Castagnoli 2010): does the
skeptic aim to prove that proof does not exist (Sienkiewicz
2022)?



Sextus' discussions of ethics also focus on issues that
plausibly lead into skepticism. Again, there are two central
questions: whether there is anything good and bad by nature; and
whether there is an art of life (Bett 2010, 2011 and 2019),
as the Epicureans and Stoics claim there is. If we could settle what
is good and what is bad, some of the most disturbing anomalies would
be resolved. If there were an art of life, there would be a teachable
body of knowledge about the good and the bad. In both cases, questions
that can cause a great deal of puzzlement would be resolved.
Sextus' discussions of ethics are in part famous because Sextus
ascribes outlandish and shocking views to the Stoics. As Sextus
construes his arguments, the contrast between 'ordinary
life' and philosophical views leads to suspension of judgment
(Vogt 2008a, ch. 1). In the modern tradition, a number of philosophers
including Hegel and Nietzsche have engaged with aspects of
Sextus' outlook and in particular with the skeptical adherence
to ordinary life (Berry 2010 and 2020; Bett 2020a). Recently,
scholars have asked how ethical a skeptic can be, to use a phrased
employed by Bett (2019), given that it may seem that suspension of
judgment on grave ethical challenges can seem facile. At the same
time, scholars point out that some dimensions of ethical frameworks
went unquestioned a long time, for example, with respect to gender;
here suspension of judgment may appear innovative (Olfert
forthcoming).



The books on physics discuss god, cause, matter, bodies, mixture,
motion, increase and decrease, subtraction and addition, whole and
part, change, becoming and perishing, rest, place, time, and number.
Notably, god is one of the topics explored in physics. This stands in
stark contrast to medieval and early modern discussions, where the
quest for knowledge of God often frames and motivates engagement with
skepticism. In PH 3, Sextus prefaces his discussion of arguments
for and against the existence of gods by saying that the
skeptics' ordinary life without opinions
(*adoxastos*) includes the following: the skeptics say
that there are gods, are pious toward the gods, and say that the gods
are provident. Scholars discuss how this relates to Sextus'
discussions of theology qua topic in physics on the one hand (PH
3.2-12, M 9.11-194), and to his portrayal of the skeptics'
ordinary life in PH 1 on the other hand (Annas 2011, Veres 2020a). The
skeptics come to suspend judgment on all central questions in ancient
physics (Bett 2012). This means, they come to suspend judgment on
whether, for example, there are causes, time, place, and bodies (cf.
Bobzien 2015 and Warren 2015). Their suspension does not merely mean
that they have not yet found a satisfying theory of, say, body. It
means that they find themselves unable to say whether there is body
(Burnyeat 1997). (On the cumulative force of these arguments, see
section 5.4.)



The six books entitled *Against those in the Disciplines*
(*M* 1-6) have traditionally received less attention.
Only in the last few years have scholars begun to explore them with
the kind of philosophical subtlety that has been brought to bear in
the study of ancient skepticism in recent decades. *M*
1-6 skeptically examine six fields of study, namely grammar,
rhetoric, geometry, arithmetic, astronomy, and music-theory. Sextus
begins with an astonishing move. Contrary to his usual strategy of
emphasizing the distance between skeptics and dogmatists, he admits
that Pyrrhonians and Epicureans share much in viewing standard
disciplines as useless (*M* 1.1-7; cf. Thorsrud 2019).
Generally speaking, increased attention to *M* 1-6 may
provide additional occasion to modify the long-standing assumption
that the Stoics are Sextus' most important dogmatic
interlocutors. Throughout *M* 1-6, resonances between
Epicurean and Pyrrhonian philosophy are remarkably visible (Bett 2018,
"Introduction"). Engagement with Epicurean philosophy
shapes Sextus' approach deeply, to the extent that both schools,
Stoics and Epicureans, should be considered fundamental points of
reference.



After his remarks on how Pyrrhonians and Epicureans take issue with
the presumed usefulness of the disciplines, Sextus lays out general
arguments, suitable for skeptical examination of any field. He argues
that, for there to be a discipline, there must be the matter being
taught, the teacher, the learner, and the means of learning. If,
however, neither of these things exists, then the discipline
doesn't exist. This is how Sextus proceeds. He argues, or seems
to argue, for the non-existence of the disciplines (*M* 1.9).
Already in the very first sentence of *M* 1, Sextus describes
his own approach as one of putting forward counterarguments, a
strategy that he mentions repeatedly throughout *M*
1-6.



These moves give rise to the most contentious question regarding
*M* 1-6. Are these books negatively dogmatic? Or do they
fit in with Sextus's outlook in *PH* 1-3, where
skeptical arguments are described as leading up to suspension of
judgment? Bett (2018, "Introduction") argues that, with
some qualifications, Sextus' approach is to be explained as
follows. Sextus lays out counterarguments based on the assumption that
the arguments of the dogmatists have already been formulated. For
there to be arguments of equal weight on both sides, only the
anti-dogmatic arguments need to be adduced. The intended effect is
that jointly, these opposing sets of arguments lead us to suspend
judgment. In addition, Bett notes that the remarkable emphasis on
counterarguments, non-existence, and uselessness suggests that some of
the material in *M* 1-6 goes back to an earlier phase of
Pyrrhonism.



In four of the six fields, namely grammar, rhetoric, music, and
astrology, Sextus admits non-technical versions into the
skeptic's life, while subjecting all theoretical claims to
skeptical examination. For example, he distinguishes between the
ordinary ability to read and write on the one hand and grammar as a
technical discipline on the other, or the ability to play a musical
instrument on the one hand and music theory on the other (cf. Corti
2015b on why this kind of contrast does not come up in the books on
arithmetic and geometry, Corti 2015c on Sextus' attack on
the Platonic-Pythagorean notion of the Two, and Corti
forthcoming).



It is remarkable that, qua theoretical field, Sextus examines
astrology rather than astronomy. The latter would make for a more
typical sequence: apart from the fact that in Sextus, logic is
considered part of philosophy rather than a "discipline,"
the six fields otherwise correspond to the so-called trivium of
grammar, logic, and rhetoric and quadrivium of arithmetic, geometry,
astronomy, and music theory. Sextus' attention to astrology
rather than astronomy highlights a deep feature of his philosophy
(Corti 2015, Bett 2018). Astronomy, from Sextus' point of view,
is concerned with appearances; and hence there is a sense in which the
skeptic does not object to it. Astronomy, then, is the
"version" of astrology that skeptics can admit into their
adherence to ordinary life (*M* 5.1-3). Presumably,
astronomy is concerned with predicting things like droughts, floods,
earthquakes, and plagues based on appearances. Astrology, on the other
hand, is concerned with matters of great obscurity.


## 5. Ancient and Modern Skepticism: Transitions


### 5.1 Augustine: Re-Conceiving Skepticism in a Theological Framework



Historians of philosophy sometimes argue that Henri Etienne's
rediscovery of Sextus in 1562 initiated an era of epistemology. Early
modern engagement with skepticism is here seen as a turn to arguments
found in Sextus (Annas-Barnes 1985, 5-7; Bailey 2002,
1-20). Via Cicero, early modern and modern philosophers seem to
have engaged also with Academic arguments (for a recent analysis of
Academic skepticism in Hume and Kant, cf. Gonzalez Quintero
2022). In particular the beginning of Descartes'
*Meditations* may display a kind of Socratic spirit: a
commitment to calling into question all one's beliefs. However,
early modern philosophers work within a theologically framed tradition
that importantly begins with St. Augustine (354-430) (cf. Menn
1998 and Lagerlund 2009; on the history of medieval skepticism cf.
Lagerlund ed. 2009; cf. Carriero 2009 on Descartes' engagement
with Aquinas; for an analysis of the transformation of skepticism that
turns immediately to Descartes, cf. Williams 2010).



A major part of Augustine's early education consisted in the
study of Cicero's writings. He was thus closely acquainted with
Academic skepticism (Cicero was one kind of Academic skeptic).
Augustine sees the force of ancient skeptical strategies. Even though
he does not become a skeptic, he integrates distinctively skeptical
moves into his thought. This has a long-standing effect on the history
of theology and science. For example, Galileo Galilei is able to cite
Augustine when he defends himself against the charge that his physics
is in opposition to the Bible (*Letter to the Grand Duchess*,
in Drake 1957). Augustine supplies arguments to the effect that we
should keep an open mind. Both our physical theories and our
interpretations of the Bible are likely to evolve. This idea figures
importantly in Pyrrhonism. Past experience tells us that, on every
given issue, someone eventually came up with a new argument.
Accordingly, even if the skeptics cannot find an objection to a given
claim right now, they expect that in the future, a conflicting view
will be formulated.



However, such traces of skepticism are integrated into an ultimately
non-skeptical philosophy. In *Contra Academicos*, Augustine
recognizes a core feature of ancient skepticism, namely that it is a
commitment to ongoing inquiry (cf. Nawar 2019 on Augustine's
defense of knowledge against the skeptics in *Contra
Academicos* 3). The question that Augustine considers vital, then,
is whether a life devoted to inquiry can be compelling, if seemingly
there is no prospect for ever attaining truth (cf. Lagerlund 2009). It
is as a philosophy of inquiry that skepticism makes a lasting
contribution to ethics, continuing, as it were, a Socratic legacy
(Vogt 2017).



Augustine creates the framework that will become characteristic of
early modern discussions. First, in his work skeptical arguments are
explored in order to be refuted. Second, the key issue is whether we
have knowledge, not whether we should hold anything to be true. In
Augustine, the background for caring so much about knowledge is the
pressing question of whether we can know God: whether we can know that
he exists and what his properties are. This might also be the reason
why knowledge of testimony gains importance (*De Trinitate*,
15.12; in Schoedinger 1996). The Bible, or parts of it, might be
considered testimony about God, and accordingly as one possible way of
attaining knowledge of God.



Third, in the process of asking whether we can have knowledge of God
it makes sense to distinguish between kinds of knowledge (sensory,
rational, by testimony, etc.). If we know God, then we do so via one
of the kinds of knowledge. This becomes a standard feature of
discussions of skepticism. Philosophers go through the different kinds
of knowledge that are conceivable, and examine them in turn. In
Augustine as well as later authors, this includes mathematical
knowledge (Nawar 2022). Though Sextus wrote on geometry and
arithmetic, questions about knowledge in mathematics do not shape
Hellenistic debates between skeptics on the one hand and Epicureans
and Stoics on the other hand. Fourth, Augustine conceives of what he
calls 'inner knowledge.' He envisages a skeptical
scenario. Suppose we have no sensory knowledge, no rational knowledge,
and no knowledge of testimony. We still know that we think, love,
judge, live, and are (*De Trinitate* 15.12). In the *City of
God* 11.26, Augustine uses his well-known phrase "*si
enim fallor, sum*" (even if I err, I am). That is, Augustine
suggests that we have knowledge of our mental acts (cf. Nawar 2022 on
Augustine's concern with self-knowledge). However, Augustine
does not consider these pieces of knowledge foundational. While he
points to them when he discusses the challenges of Academic
skepticism, he does not systematically build upon them in refuting
skepticism about sense perception, rational knowledge, and knowledge
of testimony. Rather, he refutes skepticism by stating that God
created us and the things that are known to us; God wanted these
things to be known to us (*De Trinitate* 15.12). In later
epistemology, the idea of the turn into one's mind and an
introspective access to one's mental acts becomes a secular
idea. Augustine is a transitional figure in the philosophy of mind,
and thereby re-conceives skepticism. By focussing on a gap between
'what is in the mind' and the world outside, he as it were
invites external world skepticism (Vogt 2014a). But Augustine is
concerned with the path to God: the mind turns into itself and
from there it moves further, toward God (e.g., *Confessions* 7.
17,23).



Next to Augustine, Al-Ghazali (1085-1111) plays a major role in
re-conceiving the questions relevant to skepticism (Menn 2003,
Kukkonen 2009). In *The Rescuer From Error*, Al-Ghazali
literally describes God as the rescuer from error (in Khalidi 2005).
Like Augustine before and Descartes after him, Al-Ghazali moves
through different cognitive faculties. Do the senses or reason allow
us to gain knowledge? These questions are framed by the quest for
knowledge of God. While Augustine thinks that knowledge of God comes
through a combination of seeking God on the one hand and God's
grace on the other, Al-Ghazali thinks it comes through spiritual
exercises. However, once confidence in God is secured, trust in the
more familiar ways of gaining knowledge--sense perception,
rational reasoning, and so on--is restored (for a detailed
treatment of skepticism in Classical Islam, cf. Heck 2014).



One key difference between ancient skepticism on the one hand, and
medieval as well as Cartesian skepticism on the other, is that ancient
skepticism is not framed by theological concerns. Note that in
Cartesian skepticism, God is not only invoked when it comes to
refuting skepticism. More importantly, the skeptical problems arise in
a way that depends on God as creator. Our cognitive faculties are seen
as created faculties, and the world as a created world. A kind of
'faculty-skepticism' that asks whether our cognitive
faculties are built so as to be erroneous is formulated, and a
potential gap between our minds and the world opens up. Perhaps God
made us in such a way that we are fundamentally wrong about everything
(or, as later secular versions have it, a mad scientist experiments on
a "brain in a vat").



These are important steps away from the non-theological ancient
construal of skepticism. The theological premises of early modern
skepticism are not only foreign to ancient debates; they would be seen
as misguided. From the Hellenistic point of view, theology is part of
physics. An account of god is part of an account of the natural world
(as such, it is unrecognizable as 'theology' from the
point of view of later theologies). Human beings and their cognitive
faculties are natural parts of a natural world. They are organic and
functional parts, interconnected with the other parts of the large
whole which the universe is. A mind-world-gap (of the kind envisaged
in the Cartesian tradition) is inconceivable. Each 'mind,'
and that is, rational soul, is an integrated physical part of the
physical world. Like a part of a complex organism, it would not exist
were it not for the interrelations it has with the other parts. A
physiological account of the mind makes the stark divide between mind
and world that figures in early modern skepticism unimaginable.


### 5.2 Skepticism About Induction



Contemporary discussions inherit long-standing problems from early
modern philosophy. Among them, external world skepticism, skepticism
about other minds, and skepticism about induction are particularly
prominent. In assessing ancient skepticism, we might ask whether the
ancients saw these problems.



Among the skeptical problems of modern philosophy, skepticism about
induction stands out. Its early formulation in Hume does not depend on
the idea that our faculties are created by God, who also created the
world. Hume takes himself to engage with Pyrrhonian skepticism
(Ainslie 2003). Induction proceeds from particular observations to a
general conclusion. Skepticism about induction points out that, no
matter how many particulars were observed, the general claim
pronounces also on what has not been observed. In this respect, the
inference seems unwarranted and so we should suspend judgement on its
effectiveness. Induction can concern the ascription of properties to
some kind of entity as well as causal claims. In the latter, the
skeptic observes that what regularly precedes a type of event may not
be its cause. Perhaps we cannot infer anything from the fact that
certain properties or events regularly occur together (Vlasits 2020a;
for a related argument in Al-Ghazali, cf. Kukkonen 2009).



Relevant ideas can be traced in various aspects of Sextus'
philosophy. First, Sextus sides with anti-rationalist tendencies in
medicine. According to these schools, a doctor remembers that, in
earlier cases, symptom *A* was alleviated by medication
*B*. They do not infer that medication *B* makes symptom
*A* disappear, or that the illness *C* is the cause of
symptom *A*. Second, the Five Modes do not exclusively target
proof. They address everything that lends credibility to something
else. They may thus also call into question signs that are taken as
indicative of their causes. Sextus' skeptic does not accept such
indicative signs. Third, Sextus discusses the role of so-called
commemorative signs in the skeptic's life (*PH*
2.100-102; Allen 2001). For example, a scar is a commemorative
sign of a wound. Both were co-observed in the past. A skeptic will
think of a wound when seeing a scar. But they do not commit to causal
or explanatory claims. Fourth, Sextus records a set of Causal Modes
(*PH* 1.180-86), which are specifically targeted toward
causal explanations (Corti 2014; on the relation between the Causal
Modes and Hume cf. Garrett 2020). He does not ascribe the kind of
relevance to them that the Ten Modes and the Five Modes have. Indeed,
he thinks the Five Modes can do the work of Causal Modes (that is,
call into question causal and explanatory theses and theories).
However, the Causal Modes go into great detail on how the skeptic
investigates any kind of causal thesis or theory.


### 5.3 Subjectivity and Other Minds



The distinction between subjectivity and objectivity is central to
modern discussions of skepticism. It is not envisaged in ancient
thought. However, this does not mean that ancient philosophers do not
reflect on questions relevant to this distinction. Arguably,
Pyrrhonism conceives of the affections of the mind in ways that
anticipate later thought about subjectivity (Fine 2003a and 2003b).
Sextus describes the skeptic's states of
'being-appeared-to' as affections of the mind. A skeptic
can report these states in their utterances. Illustrating this point,
Sextus uses expressions associated with the Cyrenaics, a Socratic
school of thought. These expressions literally mean something like
'I am being heated' or 'I am being whitened.'
They aim to record affections without claiming anything about the
world. Fine argues that the skeptic's beliefs are beliefs about
these affections (2000). With this proposal, Fine turns against two
prominent positions in scholarly debate about skeptical belief (see
section 4.4), that skeptics have no beliefs whatsoever, and that they
have beliefs that fall short of holding true. Fine envisages
reflective beliefs: beliefs about one's states of mind (on
related issues in contemporary epistemology, cf. Feeney and
Schellenberg 2020 and Gluer 2020).



Whether or not Sextus' account of the skeptic's mental
life includes reflective beliefs about one's mental states, we
should note an important difference to later proposals of that kind.
Later philosophers focus on the particular kind of certainty attached
to reflective knowledge. Reflective knowledge is sometimes seen as a
stepping-stone towards greater confidence in our cognitive powers, and
our ability to also attain other kinds of knowledge. But it may not be
obvious that reflective knowledge can take on this important role. In
this respect, Augustine is still closer to ancient than to modern
intuitions. He says that such pieces of knowledge as "I know
that I think" are not what we are looking for. Augustine
envisages that reflective knowledge-claims can be iterated, so that we
would have infinitely many pieces of knowledge ("I know that I
know that I think..."). But from his point of view, this
kind of knowledge leads nowhere. When we ask whether we can have
knowledge, we are interested in knowledge of the world and of God
(*De Trinitate* 15.12).



Modern philosophers also pay great attention to the privileged access
cognizers have to their own cognitive activities. Augustine introduces
a distinction that paves the way for this idea. He argues that the
mind cannot know what kind of stuff it is (*De Trinitate* 10.10
and 15.12). The mind does not know its substance, but it knows its
activities. For Augustine, this means that the mind knows itself. The
mind is precisely what it knows itself to be: in knowing that one
thinks, judges, lives, and so on, one knows the mind (Vogt 2014a).
Note that this argument indicates that knowing that one lives and is
are not pieces of knowledge about one's bodily existence, but
about the activities of the mind.



Finally, modern philosophers conceive of the special kind of access to
one's own mind not only in contrast with our access to the
world. They also compare it to our access to what goes on in other
minds. One of their core problems is skepticism about other minds. If
our own minds are accessible to us in the way nothing else is, then we
might not be able to ascribe mental states to others. For example, we
might not know that someone who looks as if she is in pain really is
in pain. The ancient skeptics envisage nothing of this kind (Warren
2011). This suggests that, insofar as they draw a distinction between
affections of the mind and the world, this distinction is construed
differently than in modern skepticism.


### 5.4 External World Skepticism



In its early modern versions, external world skepticism involves the
idea that there is a creator--someone who made the world and our
faculties, and the fit or misfit between them. If this assumption is
crucial to external world skepticism, then the ancients do not
conceive of this skeptical problem. From the point of view of modern
philosophy, ancient skepticism may appear limited by not addressing
some of the most radical skeptical scenarios (Burnyeat 1980 [1997] and
1982; Williams 1988; Fine 2003a and 2003b). From the point of view of
ancient skepticism, early modern skepticism and the long life that its
problems enjoy, however, would seem to originate in a flawed
theology.



Contemporary philosophers sometimes discuss external world skepticism
in terms of a paradox: one thinker finds herself torn between the
strength of skeptical arguments and her ordinary convictions. For
example, she thinks that *this is her hand.* But she concedes
that the skeptical hypothesis that a mad scientist might have set
things up so that she has such perceptions and thoughts (the so-called
brain in a vat scenario) is hard to refute. This way of framing
discussions of skepticism is foreign to antiquity. In antiquity,
skeptics and their opponents are different thinkers, each of them with
one set of intuitions, arguing against each other. It is also foreign
to ancient skepticism insofar as it inherits the early modern idea
that some greatly powerful agent sets things up, and in a sense
creates the thinker's faculties and the world as it appears to
them.



However, the ancient skeptics might conceive of their own kind of
external world skepticism. One way to explore this question is to turn
to the way in which Sextus describes that which is outside of the
skeptic's mind (Fine 2003 and 2003(2)). Throughout his work,
Sextus employs the distinction between appearances and what really is
the case. Consider some of the detail of how he characterizes the
latter. One phrase in the Ten Modes is "*ta ektos*
*hupokeimena*," the externally underlying things
(*PH* 1.61, 127, 128, 134, 144). Other phrases, meant to
demarcate roughly the same contrast with appearances, are how things
are in their nature (*phusei*) (*PH* 1.78, 123, 140),
"the underlying things" (*hupokeimena*)
(*PH* 1.106), as well as a combination: "the nature of
the underlying external things" (*PH* 1.117, 163). The
expressions which contain the word "external" might read
as if Sextus was talking about the external world in a sense familiar
to us from early modern skepticism.



But what are the underlying or external objects, as Sextus conceives
of them? For example, Sextus speaks of the underlying reality of
whether honey really is sweet (*PH* 1.19). In such a case, it
is assumed that there are ordinary objects. But we do not have access
to the properties they really have (Fine calls this Property
Skepticism, 2003b). However, external objects in Sextus' sense
also include objects that later philosophers would not obviously see
as part of the external word. For example, an answer to the question
of what kind of life really is good would count as a claim about
external or underlying reality (cf. Pellegrin 2010).



Another approach to the question of whether Sextus envisages some kind
of external world skepticism is to turn to his discussions of physics.
Ordinarily we take ourselves to live in a world in which there are
bodies, movement, place, time, and so on. But as Sextus argues, we do
not have compelling accounts of any of these core conceptions of
physics. This leads to suspension of judgment on whether there are
bodies, movement, place, time, and so on. Sextus' discussions of
physics might add up to a rather far-reaching skepticism about the
natural world.