Skeptics those ancient thinkers who developed sets of arguments to show either that no knowledge is possible (Academic Skepticism) or that there is not sufficient or adequate evidence to tell if any knowledge is possible. If the latter is the case then these thinkers advocated suspending judgment on all question concerning knowledge (Pyrrhonian Skepticism).
Academic Skepticism gets its name from the fact that it was formulated in Plato’s Academy in the third century B.C., starting from Socrates’ statement, ‘All I know is that I know nothing.’ It was developed by Arcesilaus (c.268–241) and Carneades (c.213–129), into a series of arguments, directed principally against the Stoics, purporting to show that nothing can be known. The Academics posed a series of problems to show that what we think we know by our senses may be unreliable, and that we cannot be sure about the reliability of our reasoning. We do not possess a guaranteed standard or criterion for ascertaining which of our judgments is true or false. Any purported knowledge claim contains some element that goes beyond immediate experience. If this claim constituted knowledge we would have to know something that could not possibly be false. The evidence for the claim would have to be based on our senses and our reason, both of which are to some degree unreliable. So the knowledge claim may be false or doubtful, and hence cannot constitute genuine knowledge. So, the Academics said that nothing is certain. The best we can attain is probable information. Carneades is supposed to have developed a form of verification theory and a kind of probabilism, similar in some ways to that of modern pragmatists and positivists. Academic Skepticism dominated the philosophizing of Plato’s Academy until the first century . . While Cicero was a student there, the Academy turned from Skepticism to a kind of eclectic philosophy. Its Skeptical arguments have been preserved in Cicero’s works, Academia and De natura deorum, in Augustine’s refutation in his Contra academicos, as well as in the summary presented by Diogenes Laertius in his lives of the Greek philosophers. Skeptical thinking found another home in the school of the Pyrrhonian Skeptics, probably connected with the Methodic school of medicine in Alexandria. The Pyrrhonian movement traces its origins to Pyrrho of Elis (c.360–275 B.C.) and his student Timon (c.315–225 B.C.). The stories about Pyrrho indicate that he was not a theoretician but a practical doubter who would not make any judgments that went beyond immediate experience. He is supposed to have refused to judge if what appeared to be chariots might strike him, and he was often rescued by his students because he would not make any commitments. His concerns were apparently ethical. He sought to avoid unhappiness that might result from accepting any value theory. If the theory was at all doubtful, accepting it might lead to mental anguish. The theoretical formulation of Pyrrhonian Skepticism is attributed to Aenesidemus (c.100– 40 B.C.). Pyrrhonists regarded dogmatic philosophers and Academic Skeptics as asserting too much, the former saying that something can be known and the latter that nothing can be known. The Pyrrhonists suspended judgments on all questions on which there was any conflicting evidence, including whether or not anything could be known. The Pyrrhonists used some of the same kinds of arguments developed by Arcesilaus and Carneades. Aenesidemus and those who followed after him organized the arguments into sets of ‘tropes’ or ways of leading to suspense of judgment on various questions. Sets of ten, eight, five, and two tropes appear in the only surviving writing of the Pyrrhonists, the works of Sextus Empiricus, a third-century A.D. teacher of Pyrrhonism. Each set of tropes offers suggestions for suspending judgment about any knowledge claims that go beyond appearances. The tropes seek to show that for any claim, evidence for and evidence against it can be offered. The disagreements among human beings, the variety of human experiences, the fluctuation of human judgments under differing conditions, illness, drunkenness, etc., all point to the opposition of evidence for and against each knowledge claim. Any criterion we employ to sift and weigh the evidence can also be opposed by countercriterion claims.
Given this situation, the Pyrrhonian Skeptics sought to avoid committing themselves concerning any kind of question. They would not even commit themselves as to whether the arguments they put forth were sound or not. For them Skepticism was not a statable theory, but rather an ability or mental attitude for opposing evidence for and against any knowledge claim that went beyond what was apparent, that dealt with the non-evident. This opposing produced an equipollence, a balancing of the opposing evidences, that would lead to suspending judgment on any question. Suspending judgment led to a state of mind called ‘ataraxia,’ quietude, peace of mind, or unperturbedness. In such a state the Skeptic was no longer concerned or worried or disturbed about matters beyond appearances. The Pyrrhonians averred that Skepticism was a cure for a disease called ‘dogmatism’ or rashness. The dogmatists made assertions about the non-evident, and then became disturbed about whether these assertions were true. The disturbance became a mental disease or disorder. The Pyrrhonians, who apparently were medical doctors, offered relief by showing the patient how and why he should suspend judgment instead of dogmatizing. Then the disease would disappear and the patient would be in a state of tranquillity, the peace of mind sought by Hellenistic dogmatic philosophers.
The Pyrrhonists, unlike the Academic Skeptics, were not negative dogmatists. The Pyrrhonists said neither that knowledge is possible nor that it is impossible. They remained seekers, while allowing the Skeptical arguments and the equipollence of evidences to act as a purge of dogmatic assertions. The purge eliminates all dogmas as well as itself. After this the Pyrrhonist lives undogmatically, following natural inclinations, immediate experience, and the laws and customs of his society, without ever judging or committing himself to any view about them. In this state the Pyrrhonist would have no worries, and yet be able to function naturally and according to law and custom. The Pyrrhonian movement disappeared during the third century A.D., possibly because it was not considered an alternative to the powerful religious movements of the time. Only scant traces of it appear before the Renaissance, when the texts of Sextus and Cicero were rediscovered and used to formulate a modern skeptical view by such thinkers as Montaigne and Charron. See also SEXTUS EMPIRICUS, SKEPTICIS. R.H.P.