Sextus Empiricus (fl. during the 2nd and possibly the 3rd centuries AD), was a physician and philosopher, and has been variously reported to have lived in Alexandria, Rome, or Athens. His philosophical work is the most complete surviving account of ancient Greek and Roman skepticism.

In his medical work, tradition maintains that he belonged to the "empiric" school (see Asclepiades), as reflected by his name. However, at least twice in his writings, Sextus seems to place himself closer to the "methodic" school, as his philosophical views imply.

Sextus' Writings

Sextus Empiricus's three known works are the Outlines of Pyrrhonism (Pyrrhoneioi hypotyposeis), and two distinct works preserved under the same title, Against the Mathematicians (Adversus Mathematicos), one of which is probably incomplete.

The first six books of Against the Mathematicians are commonly known as Against the Professors, but each book also has a traditional title (Against the Grammarians (book I), Against the Rhetoricians (book II), Against the Geometricians (book III), Against the Arithmeticians (book IV), Against the Astrologers (book V), Against the Musicians (book VI)). It is widely believed that this is Sextus's latest and most mature work.

Books VII-XI of Against the Mathematicians form an incomplete whole; scholars believe that at least one, but possibly as many as five books, are missing from the beginning of the work. The extant books have the traditional titles Against the Logicians (books VII-VIII), Against the Physicists (books IX-X,) and Against the Ethicists (book XI).

Against the Mathematicians VII-XI is sometimes distinguished from Against the Mathematicians I-VI by giving it the title Against the Dogmatists (in which case Against the Logicians are called books I-II, Against the Physicists are called books III-IV, and Against the Ethicists is called book V, despite the fact that it is commonly believed that the beginning of the work is missing and it is not known how many books might have preceded the extant books).

Note that none of these titles except Adversus Mathematicos (Against the Mathematicians) and Outlines of Pyrrhonism, are found in the manuscripts.


Sextus Empiricus advises that we should suspend judgment about virtually all beliefs, that is, we should neither affirm any belief as true nor deny any belief as false. This view is known as Pyrrhonian skepticism, as distinguished from Academic skepticism, as practised by Carneades, which, according to Sextus, denies knowledge altogether.

Sextus did not deny the possibility of knowledge. He criticizes the Academic skeptic's claim that nothing is knowable as being an affirmative belief. Instead, Sextus advocates simply giving up belief: that is, suspending judgment about whether or not anything is knowable. Only by suspending judgment can we attain a state of ataraxia (roughly, 'peace of mind'). Sextus did not think such a general suspension of judgment to be impractical, since we may live without any beliefs, acting by habit.

Sextus allowed that we might affirm claims about our experience (e.g., reports about our feelings or sensations). That is, for some claim X that I feel or perceive, it could be true to say "it seems to me now that X." However, he pointed out that this does not imply any objective knowledge of external reality. For while I might know that the honey I eat tastes sweet to me, this is merely a subjective judgment, and as such may not tell me anything true about the honey itself.

Interpretations of Sextus' philosophy along the above lines have been advocated by scholars such as Myles Burnyeat, Jonathan Barnes, and Benson Mates.

Michael Frede, however, defends a different interpretation, according to which Sextus does allow beliefs, so long as they are not derived by reason, philosophy or speculation; a skeptic may, for example, accept common opinions in the skeptic's society. However, the content of such beliefs is purely conventional or subjective. Thus, on this interpretation, the skeptic may well entertain the belief that God does or does not exist or that virtue is good. But he may not believe that such claims are true by nature.

Sextus' Legacy

An influential Latin translation of Sextus' "Outlines" was published by Henricus Stephanus in Geneva in 1562. Petrus and Jacobus Chouet published the Greek text for the first time in 1621. Stephanus did not publish it with his Latin translation either in 1562 or in 1569, nor was it published in the reprint of the latter in 1619. Sextus's "Outlines" were widely read in Europe during the 16th, 17th and 18th centuries, and had a profound impact on Michel de Montaigne, David Hume, and Hegel, among many others. Another source for the circulation of Sextus's ideas was Bayle's Dictionary.

The legacy of Pyrrhonism is described in Richard Popkin's The History of Skepticism from Erasmus to Descartes and High Road to Pyrrhonism. The transmission of Sextus's manuscripts through antiquity and the Middle Ages is reconstructed by Luciano Floridi's Sextus Empiricus, The Recovery and Transmission of Pyrrhonism. Oxford: Oxford University Press, 2002.