Active around AD 200

Sextus Empiricus

Ask for the reason behind any claim, then the reason behind the reason. The Pyrrhonian sceptics showed that the questioning can end in only three ways, all of them bad, and drew the conclusion that we should stop believing.

The view

Almost nothing is known about Sextus except that he was a physician and wrote in Greek. His Outlines of Pyrrhonism is the fullest surviving account of ancient scepticism, a tradition that traced itself to Pyrrho of Elis some five centuries earlier.

Scepticism, as Sextus describes it, is a skill and not a doctrine: the ability to set against any appearance or argument another of equal weight. Faced with two cases he cannot choose between, the sceptic suspends judgement, a state called epochē. And then something unexpected follows: peace of mind. Sextus tells the story of the painter Apelles, who could not get the foam on a horse's mouth right, flung his sponge at the picture in disgust, and found that the splash had painted it for him. The sceptics went looking for calm by settling what is true. They found it when they gave up.

The sceptic still lives an ordinary life. He eats when hungry, follows the customs of his city and practises a trade. He goes by how things appear and declines to say how they really are.

The argument

The sharpest weapons are the five modes that Sextus attributes to "the more recent sceptics" and that an earlier source credits to Agrippa. Two of them, disagreement and relativity, raise the challenge: on every question people differ, and things appear differently from different positions. The other three block every exit.

What is offered as support for a claim itself needs support, and that another, without end. The mode of regress, Outlines I.166, paraphrased

If you do not go on for ever, you either stop at something you simply assume, which your opponent may deny with equal right, or you circle back to what you were trying to prove. Regress, assumption, circle: the German philosopher Hans Albert, a follower of Popper, later named this the Münchhausen trilemma, after the baron who pulled himself out of a swamp by his own hair.

Where he meets Deutsch

The trilemma is sound, and Deutsch accepts it without reservation. No belief can be justified: not by the senses, not by reason, not by authority. Certainty is not available. Every philosopher who has tried to refute the sceptic by finding the secure foundation has failed, and Descartes is the grandest failure.

Sextus also has the right enemy. He calls his opponents dogmatists: people who think the matter is closed. Deutsch uses the same word for the same fault.

Where they part

Sextus and his opponents share one premise: that a claim deserves acceptance only if it is justified. The dogmatist says some claims are; the sceptic shows that none is, and so accepts none. Deutsch, following Popper, rejects the premise. Theories are not held because they have been justified. They are guesses, held tentatively, and kept for as long as they survive criticism better than their rivals. The trilemma destroys justification and leaves criticism untouched.

The practical difference is large. The Pyrrhonist's reward is tranquillity, and a life lived by custom and appearance. He will never be wrong, because he asserts nothing. He will also never build a telescope. Deutsch wants error, found and corrected: without bold claims about how things really are, there is nothing to correct and nothing to learn.

See every view compared →

Further reading

• Sextus Empiricus, Outlines of Scepticism, translated by Julia Annas and Jonathan Barnes (Cambridge, 2000). Book I.164–177 for the five modes.
• Hans Albert, Treatise on Critical Reason (1968; English translation Princeton, 1985), for the Münchhausen trilemma.
• Sextus Empiricus and Ancient Skepticism, Stanford Encyclopedia of Philosophy.