ANCIENT SKEPTICISM

Tradition recognizes two schools of ancient skepticism: the Academics and the Pyrrhonists. The ancient Greek term "skeptic" was used by the Pyrrhonists to describe themselves. They denied that it described the Academics, but this point could be and was disputed, and later in antiquity the word may have been used as a common designation for both schools. Our use of the term in this way goes back to the seventeenth century.

The term itself is derived from a verb in common use meaning "to inquire" or "to investigate"—hence the skeptic as inquirer. This is a surprise. We take skepticism, roughly speaking, to imply a denial of the possibility of knowledge. Yet Sextus Empiricus, the second-century CE Pyrrhonist—and the only member of the school whose works have survived intact and in bulk—is quite firm on this point. In the opening chapter of his Outlines of Pyrrhonism, he distinguishes three types of philosophers: those who take themselves to have discovered the truth, those who hold that it cannot be apprehended, and those who persist in inquiring. Philosophers of the first type he calls "dogmatists," members of the last group "skeptics," and those of the middle tendency "Academics."

This is unfair. Even Academics like Philo of Larissa, who did hold that nothing can be apprehended, did not conclude from this that inquiry was pointless. Though they held that certain knowledge was unobtainable, they believed that it was possible to identify views that enjoyed a high degree of probability or verisimilitude—among them, the view that nothing can be known for certain—and they regarded inquiry for the sake of such discoveries as eminently worthwhile. What is more, Academics like Carneades and Clitomachus were no more convinced that nothing can be known than the Pyrrhonists, and they and deserved to be described as inquirers at least as much.

These facts only add to the puzzle, however. If not only the Pyrrhonists but also many Academics were skeptics in Sextus's sense, why the persistent tendency, beginning with the ancient skeptics' own contemporaries, to equate skepticism with one of the positions that Sextus expressly opposes to it? And why should a dedication to inquiry set the skeptics apart from members of other schools? Philo of Alexandria, who was active in the first century CE, was able to use the term "skeptikos" (in the sense of "inquirer") of philosophers quite generally.

Sextus's idea seems to be this: Inquiry into a particular question comes to a natural end either when the question that set the inquiry in train is resolved or when it becomes plain that it cannot be resolved. Absent either outcome, further inquiry is indicated. Dogmatists take themselves to have brought many inquiries to a successful conclusion in the first way. Negative dogmatists, or dogmatic skeptics as we may also call them, have satisfied themselves that the questions are beyond resolution. By contrast, skeptics, properly so called, find that question after question remains open and hence calls for further inquiry. On their view, dogmatists of both the positive and negative variety were guilty of calling off their inquiries prematurely. And the fault about which ancient skeptics complain most frequently is rashness or precipitate judgment.

The condition in which skeptics find themselves regarding the questions they investigate resembles that of negative dogmatists or dogmatic skeptics in being one of not knowing. But those who saw Academics and Pyrrhonists as skeptics in the modern sense were not simply confusing the condition of the inquirer with the dogmatic rejection of the possibility of knowledge. They were reacting to the fact that skeptics of both schools devoted far more time and energy to the case that nothing can be known than to arguments bearing on any other question.

The reason for this seems to be the following: It is possible to pursue unresolved inquiries into all sorts of questions without ever doubting that knowledge is, at least sometimes, achievable. But it is also possible to make the nature and possibility of knowledge an object of inquiry. If questions about knowledge remain stubbornly open, one of the things that one will not know, and that will require further study, is whether one can know at all; and from this central epistemological question the skeptical condition will spread to other inquiries, which can be brought to a conclusion only by justified claims to knowledge that the skeptic cannot make with confidence about anything. The inquiry into the possibility of knowledge remains open because of the persistent lack of satisfactory answers to the powerful arguments that knowledge is impossible. And ancient skeptics pursued the inquiry into the nature and possibility of knowledge chiefly by confronting the best theories of knowledge with these arguments.

Because the ancient skeptics consistently declined to make knowledge claims and constantly argued that nothing can be known, it is hardly surprising that outsiders took them to hold the position that nothing can be known and to hold it because they were convinced by the arguments they advanced in support of it. But if, in deference to tradition, we call this position the skeptical position and arguments supporting it skeptical arguments, for most ancient skeptics, being a skeptic was not a matter of holding the skeptical position in this traditional sense, and their reason for arguing skeptically was not to establish or defend the skeptical position. Rather, their skepticism was a matter of being unable to terminate the inquiries in which they were engaged—chiefly about the possibility of knowledge, but about the other matters as well.

Precursors

The history of ancient Greek philosophy before the emergence of the main skeptical schools contains many figures who expressed doubts about the possibility of knowledge. Some of these were collected by skeptical Academics in order to provide themselves with a distinguished lineage.

Already in the sixth century BCE, the pre-Socratic philosopher Xenophanes composed some verses about the impossibility of human beings ever knowing for sure whether they had hit upon the truth or not. Perhaps the most important pre-Socratic precursor of skepticism was Democritus, who observed that his theory of atomism, which he took to be based ultimately on the evidence of the senses, had the consequence that the senses were unreliable, since the colors and flavors with which they appear to put us in contact would have no real existence if he were correct. It was characteristic of Academic argument especially, but also of many Pyrrhonian arguments, to proceed in the same way by deducing consequences imperiling the possibility of knowledge from dogmatic theories about knowledge. Though we are not well informed about the details, it is clear that a tradition calling the possibility of knowledge into question arose among philosophers influenced by Democritus. They include Metrodorus of Chios (fourth century BCE), whose work on nature begins, "None of us knows anything, not even this, whether we know or do not know," and Pyrrho of Elis (circa 365–275 BCE), who is traditionally, though probably wrongly, viewed as the founder of the school which bears his name.

Unsurprisingly, skeptical Academics in search of illustrious antecedents appealed to the example of Socrates, who was the teacher of the Academy's founder, Plato, and well known for claiming that he knew nothing except perhaps that he knew nothing. This was Socrates' explanation for the pronouncement of the oracle in Delphi that he was the wisest man in Greece. The wisdom that set him apart from others, he conjectured, could only be his recognition that he lacked knowledge, whereas others, who were no more knowledgeable, deluded themselves and others into believing that they had knowledge.

Academic skeptics were inspired by at least two other characteristics of Socrates. First, though he set the highest possible value on knowledge and devoted his life to the pursuit of wisdom, Socrates lived an exemplary life without having attained it, thus providing the Academic skeptics with a model of the life they took themselves to be leading. Second, Socrates was a master of dialectic. A dialectical argument involves two parties: a questioner and an answerer. The answerer commits himself to a thesis, which it is his task to defend. The questioner aims to construct an argument to the contradictory of the answerer's thesis from grounds acceptable to the answerer, and he poses his questions with this end in view. When the questioner succeeds, it is through an argument all of whose premises have been conceded by the answerer. The answerer is thereby shown to lack the kind of understanding of the subject under discussion that Socrates' interlocutors typically claimed. The dialectical inquiry thus exposes problems inherent in the answerer's position or his defense of it or both. Since this kind of refutation can be accomplished by a questioner with no independent knowledge of the matters in contention, dialectical argument recommended itself to committed inquirers like Socrates, and it became the principal method of the Academic skeptics, who drew their inspiration from him.

Attempts were also made in the Academy to interpret Plato as a skeptic. The argument is based on his many expressions of caution and his manifest willingness in the dialogues to raise difficulties without resolving them. Whatever the merits of this claim, questions about the possibility of knowledge were not as prominent among Socrates' and Plato's concerns as they were among those of the Academics and Pyrrhonians.

Although book 9 of Diogenes Laertius's Lives and Opinions of Eminent Philosophers (the fullest treatment Pyrrhonism apart from Sextus Empiricus) includes a list of Pyrrhonists extending from Pyrrho to Sextus and beyond, the first part of it is almost certainly a construction. Pyrrho should probably not be viewed as the founder of a skeptical school. The modern scholarly consensus is that the Pyrrhonian school was founded in the first century BCE by Aenesidemus, who appears to have been an Academic dissatisfied with what he saw as the drift to dogmatism in the Academy of his time. He and his followers seem to have turned to Pyrrho in an effort to create an alternative history of skepticism that would make his school the legitimate heir of an older skeptical tradition.

Pyrrho wrote nothing but made a strong impression on his contemporaries, at least as much through his character as through his teachings. Figures with no sympathy for the positions he is thought to have held praised his imperturbability, lack of conceit, and tranquility. His views are elusive, however. Cicero seems to have known of him only as a moralist. He grouped Pyrrho together with figures like the heterodox Stoic Aristo of Chios (third century BCE). Such thinkers, he maintains, by making virtue the sole human good, fail to supply it with an object outside itself and so produce ethical theories incapable of furnishing practical guidance. The poet Timon of Phlius (c. 325–c. 238 BCE) became a follower of Pyrrho, whom he celebrated in a number of works that were probably the later Pyrrhonists' principal source of information about Pyrrho.

There was enough of an affinity between Pyrrho and Arcesilaus, the school leader of the Academy responsible for its skeptical turn, for their relationship to be the subject of a satirical verse by Aristo. Later on the characteristics of the Pyrrhonian school were imputed to Pyrrho. But whether and in what way Pyrrho was himself a skeptic remains subject to controversy. The most complete surviving account of his views is a late antique quotation of a first century CE citation of Timon. According to it, Pyrrho maintained that "things are equally indifferent, unmeasurable, and undecidable," and he went on to say that "neither our perceptions nor our opinions are true or false." According to one school of interpretation, the first claim is best viewed an epistemological thesis that Pyrrho deduced from the second, which, on this view, is an assertion about the apparent impossibility of distinguishing true from false beliefs. This interpretation would make him a skeptic, albeit probably a dogmatic one. But others have argued that the claim that "things are equally indifferent, unmeasurable, and undecidable" is a metaphysical thesis about the nature of reality from which Pyrrho inferred that perceptions and opinions cannot be true or false. In any case, he maintained that the proper response was to be without opinion, and he claimed that the result for those who attain this condition is tranquility.

Academic Skepticism

Arcesilaus (316/15–241/40 BCE) became the fifth head of the Academy after Plato and was responsible for the school's turn to skepticism. To mark this change in outlook, later ancient writers speak of Arcesilaus as the founder of the New Academy as opposed to the Old Academy of Plato and his earliest successors; sometimes the Academy of Arcesilaus and his successors is called the Middle or Second Academy to distinguish it from the New or Third Academy of Carneades and his followers. (None of these distinctions corresponds to changes in the Academy as an institution.)

Like Socrates, Arcesilaus wrote nothing but was distinguished by his mastery of dialectic in face-to-face conversation. Rather than expound or defend views of his own, he would let his interlocutors put forward a view that he would then subject to dialectical examination. His decision to make Stoic epistemology the principal object of his inquiries exerted a decisive influence on the subsequent history of ancient skepticism.

The Stoics took wisdom to mean a firm grasp of the truth, entirely free from error. They maintained that, though exceedingly rare and difficult of attainment, wisdom was nevertheless within the power of human beings. The key concept in the Stoics' account of wisdom, what they called cognitive impressions—their criterion of truth—which they define as impressions "from what is, stamped and impressed in exact accordance with what is, and such as could not be from what is not." In the paradigm case of perceptual impressions, this means that cognitive impressions arise in a way that ensures that they capture their objects with perfect accuracy, thus guaranteeing their truth, and at the same time impart to them a character that human beings can discern.

Assent to a cognitive impression is a cognition or apprehension, and, if further conditions are satisfied, it will qualify as knowledge. Assent to anything but a cognitive impression is opinion, and, according to the Stoics, the wise avoid error by remaining entirely free of opinion. Arcesilaus began the long Academic tradition of arguing that there are no cognitive impressions, which in the context of Stoic epistemology amounts to arguing that knowledge is impossible. He did this by arguing for indiscernibility—that is, he held that the character purportedly peculiar to cognitive impressions could also belong to impressions that did not arise in the required truth-guaranteeing way and were in fact false. His arguments were based as much as possible on considerations that the Stoics would have to acknowledge, either because they were drawn from Stoic theory or could be rejected only at a high cost in plausibility.

The idea that there are no cognitive impressions ("inapprehensibility" for short) was the first skeptical proposition with which the Academy came to be associated. The second, that it is incumbent on the wise to suspend judgment on all matters, Arcesilaus deduced from the first, along with the Stoic doctrine that wisdom is incompatible with opinion. Together they make up what we might call a skeptical position.

On a strictly dialectical interpretation of Arcesilaus's arguments, the conclusions he drew need tell us nothing about what views, if any, he held. The propositions that make up the skeptical position follow in the context of arguments dominated by Stoic assumptions about what is to count as knowledge and about the incompatibility of wisdom with opinion; these issues raise problems for the Stoics to solve. To be sure, Arcesilaus responded to Stoic arguments that action was impossible without assent, and assent senseless in the absence of cognitive impressions, by defending the possibility of a life in which all judgment is suspended. But this argument may only have shown that the Stoics were not in a position to easily escape the difficulties raised by his first set of arguments. And the fact that his response to the Stoics was based so closely on their theory of action as to have no force outside this debate lends support to this suggestion.

It is clear, however, that Academics after Arcesilaus interpreted him as endorsing the skeptical propositions in a certain way. This was their own view, and they may have been right about Arcesilaus. Thus a skeptical stance or outlook arose in the Academy as a result of a dialectical dispute with the Stoa that was expressed by means of the skeptical propositions. But the Academic followers of Arcesilaus seem not to have subscribed to the skeptical propositions in the ordinary way. Instead, their situation is akin to that of the skeptics described by Sextus: They were not in a position to conclude the inquiry into the nature and possibility of knowledge or other inquiries dependent on its resolution. And it is this condition that they described in terms borrowed from their debate with the Stoa—inapprehensibility and suspension of judgment—not the condition of being convinced by the arguments on their side of the debate.

We know little about Arcesilaus's successors before Carneades. Carneades was another exceptionally gifted dialectician and nonwriter. It is likely that he supplemented and refined the arguments against cognitive impressions that he inherited from his predecessors, but his most distinctive contribution was his response to the Stoics' argument that without cognitive impressions and assent, action and life are impossible. Whereas Arcesilaus's response stayed very close to Stoic theory, Carneades's did not. Instead he seems to have worked out a full-blown theory of so-called probable impressions (probabilis was Cicero's Latin translation of the Greek pithanos, meaning persuasive ). And he appealed to them to explain how life, even a life of wisdom, was possible without the perfectly secure foundation provided by cognitive impressions.

As Arcesilaus had done before him, Carneades defended the possibility of acting without assent. There is, he argued, a way of using or following probable impressions that does not amount to assent but is adequate for action and inquiry. But he also sometimes conceded that assent was essential in order to argue that even this consession did not vindicate Stoic claims about the cognitive impression. For, he suggested, it was permissible for the wise to form opinions by assenting to noncognitive impressions, opinions held in the full consciousness that they were only opinions and might be wrong.

This line of argument is behind the view that Carneades relaxed or weakened the more militantly skeptical stance of Arcesilaus. But perhaps the new features of Carneades's arguments are part of a broadly dialectical form of argument. The Stoics believe their views should win acceptance not because they are theirs but because they do justice to common assumptions about human nature—its needs and the resources available to it—as no others can. The challenge that Carneades accepted, then, was to show that the ready availability of equally sound or even better alternatives ought to discourage a premature embrace of the Stoic position.

This posture makes it hard to know whether Carneades actually subscribed to any of the views he defended. And his students and successors interpreted him in different ways. Clitomachus, his student and eventual successor, held that one should suspend judgment and that this had been Carneades's view. Philo of Larissa, who succeeded Clitomachus, contended that Carneades believed that the wise were permitted to form opinions in the absence of cognitive impressions and that one of the probable views deserving assent was inapprehensibility. Philo was, then, a dogmatic skeptic, who championed one of the skeptical propositions simply because he was convinced by the arguments for it. There is an air of paradox about this position, but it must be remembered that he did not claim to know for certain that nothing can be known for certain, but rather that it was highly probable, which, if nothing can be known for certain, is the most that can be said for it.

Pyrrhonism

It seems to have been Philo of Larissa's dogmatic skepticism that moved Aenesidemus to found or revive a competing school of Pyrrhonian skepticism in the first century BCE. The Pyrrhonian school he founded existed past the time of Sextus Empiricus, who is usually thought to have been active in the latter part of the second century CE. Although none of Aenesidemus's works have survived, a summary of eight books of his Pyrhhonian Arguments by Photius (ninth century CE) has. From it we learn that Aenesidemus, who had been an Academcie himself, charged the Academics of his time with being little more than Stoics fighting Stoics, disagreeing only about cognitive impressions while agreeing about many other issues. Though the decision by Aenesidemus and his followers to call themselves "Pyrrhonists" does not imply a direct line of descent from Pyrrho, it is probable that they were influenced by traditions about Pyrrho. Another important influence came from the Empirical school of medicine, with which Pyrrhonism maintained close ties and shared many members including Sextus Empiricus (whose name means "the Empiricist").

In view of the school's origins, it is not surprising to find many points of contact between it and Academic skepticism. The Pyrrhonists describe the skeptical condition with the aid of terms like "inapprehensibility" and "suspension of judgment," which have their origins in the epistemological debate between the Academy and the Stoa. They view this condition as the result of a standoff or impasse between their arguments and those of their dogmatic opponents, not as the result of being convinced by their own skeptical arguments. And they explain that they are able to act and to live despite suspending judgment on all questions. This argument hinges on a distinction between two senses of "belief" (Greek: dogma) that is indebted to Carneades's and Clitomachus's contrast between assenting to an impression and using or following it. In the former sense, the Pyrrhonists had no beliefs, but in the latter sense they did have beliefs, which were able to serve as a basis for action. The two works of Sextus that have come down to us, the Outlines of Pyrrhonism in three books and Against the Mathematicians in nine, are packed with arguments against dogmatic positions, many of which are of Academic origin.

There are, however, equally notable differences between the two schools, some of which may reflect other influences on Aenesidemus and his followers. The most striking and important of these is the positive value the Pyrrhonists seem to attach to the skeptical suspension of judgment about all matters. According to Sextus, Pyrrhonism has a telos, a supreme aim or goal in life: tranquility (and, where that is unattainable, moderation in one's emotions). Suspension of judgment is recommended because it gives rise to tranquility. This recommendation is not based on a theory of human nature that would explain why it finds fulfillment in tranquility. Rather the argument seems to presupposed that tranquility is humans' goal. This assumption commands greater credibility if viewed not as a claim about the essential nature of the best life for human beings, which would elicit vehement disagreement from some ancient philosophical schools, but as a weaker claim that such a life will somehow involve tranquility. And the Pyrrhonists do not pretend to be able to explain why suspension of judgment should give rise to tranquility; they claim to have made this discovery only by accident. Tranquility is supposed to arise in a manner exemplified by the famous story of Apelles the painter, who, despairing of being able paint the foam on the neck of a racing horse, gave up and threw his sponge at the painting, thereby producing by chance what he had been unable to achieve deliberately.

The idea of a correlation between freedom from opinion and tranquility may have been the Pyrrhonian school's truest debt to Pyrrho. This idea sets it clearly apart from the Academy. The Academy attached the highest value to knowledge and regarded the skeptical condition as a stop-gap, albeit a surprisingly congenial one. Asa we have seen, the Pyrrhonists were officially committed to the quest for knowledge. But the accounts of Pyrrhonism in Sextus and Diogenes Laertius give evidence of a positive attachment to suspending judgment as a means to tranquility. Arguments and argumentative strategies are recommended for their efficacy in bringing about equipollence, the condition in which arguments on either side of a question are of apparently equal force; and equipollence is cultivated not as a means to cognitive certainty but to the suspension of judgment that leads to tranquility. Thus there is a sense in which Academics like Arcesilaus and Carneades exemplified true "skepticism," in the sense of open-minded inquiry, more than the Pyrrhonists did.

There is also a difference in the kinds of arguments the two schools used. Sextus and our other sources give pride of place to the so-called modes or tropes of argument that bring about suspension of judgment. There is a set of ten such tropes, which seem to go back to Aenesidemus, and a later set of five ascribed to Agrippa, who may, however, be a fictional character in a Pyrrhonian work. (There is also a set of two tropes, and a further set of eight tropes concerning causal explanation, which is likewise credited to Aenesidemus). The ten tropes appear to be the oldest, and they draw on arguments and examples with a long history. Book Gamma of Aristotle's Metaphysics is already familiar, with arguments resembling those in the ten tropes. Most of the ten aim to demonstrate that there are undecidable conflicts between the appearances perceived by different species or different human beings or the different senses or by the same human being in different conditions or between the appearances presented by objects in different circumstances. The existence of such conflicts is illustrated by a wealth of examples, some of them fanciful. Left unclear are the exact arguments envisaged and how they relate to the official program, which calls for the production of equipollence by the balancing of arguments. The tropes seemingly aim to elicit from these conflicting appearances a thesis of undecidability thatrequires suspension of judgment. That is, it appears as though undecidability arises from an argument whose premises would command the assent of the skeptic. But perhaps the arguments for the undecidability of conflicts are meant to oppose arguments that they are decidable, and it is the equipollence between these arguments that is supposed to lead to suspension of judgment.

Even so, by comparison with Academic arguments, and with the arguments found elsewhere in Sextus, the trope-based arguments appear somewhat naive. Substantial assumptions about species, perceptual faculties, and the requisite conditions for the acceptance of an impression as true enter the argument without being marked as dialectical concessions or without comment of any kind about their status. Perhaps the material collected in the ten tropes arose from traditions of dogmatic skeptical thinking outside the Academy and maybe even from Pyrrho himself. There is a problem with the trope of relativity, which may suggest a similar conclusion about origins. According to this trope, since all things are relative, we must suspend judgment about their real natures. Though Sextus makes an attempt to correct for this, the conclusion of this argument is not, properly speaking, skeptical.

The five Agrippan modes are (i) disagreement, (ii) regress to infinity, (iii) relativity, (iv) hypothesis, and (v) circularity. Except for relativity, they form a system by means of which dogmatic attempts to justify a disputed claim can be counteracted. Any claim put forward invites disagreement. Further claims enlisted in support of it will lead to an infinite regress, by requiring justification themselves, unless the process is brought to an arbitrary halt with a hypothesis or the justification depends on the originally disputed claim. To judge from the enormous mass of arguments preserved by Sextus, neither set of tropes consistently guided the Pyrrhonists as they collected and composed arguments to further their skeptical purposes.

See also Aenesidemus; Agrippa; Aristo of Chios; Aristotle; Carneades; Cicero, Marcus Tullius; Diogenes Laertius; Dogma; Greek Academy; Leucippus and Democritus; Philo Judaeus; Philo of Larissa; Plato; Pyrrho; Sextus Empiricus; Skepticism, History of; Socrates; Stoicism; Timon of Phlius; Xenophanes of Colophon.

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James Allen (2005)