Ancient Skepticism (Part 2)

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. They take pride in arguing in a persuasive fashion for both sides of an issue. Similarly, they develop an agonistic art of refuting any claim put forward, exploiting the premises of their interlocutors and leading them into inconsistencies. 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 (§§61–73). 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). The context of the dialogue allows us to read this pronouncement as unproblematical. Socrates knows that he does not know about important things. Interpreted in this manner, Socrates does not appear to be a skeptic in the sense that he would profess to know nothing. Even though some readers (ancient and modern) found such an extreme statement in the Apology, a more plausible reading suggests that Socrates 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).

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).

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 overtly 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 eikôs 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 immediately 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 forthcoming).

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. 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.)

(End of Part 2)


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