Sextus Empiricus

Life

Almost nothing is known about Sextus Empiricus' life. He was active around 160–210 CE. His cognomen 'Empiricus' suggests he belonged to the Empirical school of medicine (which relied on experience rather than theoretical speculation about hidden causes — a natural fit for a Pyrrhonian skeptic). He may have practiced medicine in Rome, Alexandria, or Athens. He is the last known member of the Pyrrhonian skeptical tradition.

Pyrrhonian Skepticism

Sextus systematized Pyrrhonian skepticism as a philosophical practice (agōgē) rather than a doctrine. The skeptic does not assert that nothing can be known (that would be a dogmatic claim); instead, the skeptic describes an ongoing process:

1. Investigating any question with genuine openness
2. Finding equally strong arguments on both sides (equipollence/isostheneia)
3. Suspending judgment (epochē) — neither affirming nor denying
4. Experiencing, unexpectedly, the tranquility (ataraxia) that follows from release from dogmatic commitment

Sextus carefully distinguishes the Pyrrhonist from the Academic skeptic (who asserts that nothing can be known) and from the dogmatist (who asserts positive knowledge). The Pyrrhonist is a perpetual inquirer who has not yet found grounds for commitment.

The Ten Modes (Tropoi)

Sextus preserves and organizes the Ten Modes attributed to Aenesidemus — a battery of argument patterns designed to produce suspension of judgment. They include arguments from:
1. Differences among animals in perception
2. Differences among human beings
3. Differences among the senses
4. Differences due to circumstances (health, age, emotion)
5. Differences due to position, distance, and location
6. Admixtures (nothing is perceived in isolation)
7. Differences in quantity and composition
8. Relativity (all things are relative)
9. Frequency of occurrence affecting judgment
10. Differences in customs, laws, myths, and beliefs

All ten modes converge on a single conclusion: since things appear differently under different conditions, and we have no criterion for privileging one appearance over another, we should suspend judgment about how things really are.

Against the Dogmatists

In Against the Mathematicians (the title means 'Against the Professors' or 'Against the Learned'), Sextus applies skeptical arguments to every branch of knowledge. Against the logicians, he attacks the criterion of truth. Against the physicists, he challenges claims about causation, god, motion, and change. Against the ethicists, he questions whether anything is good or bad by nature. He also devotes separate books to demolishing the claims of grammar, rhetoric, geometry, arithmetic, astrology, and music.

Legacy

Sextus' works survived in Greek manuscripts and were largely unknown in the Latin West until the Renaissance. In 1562, Henri Estienne published a Latin translation of the Outlines of Pyrrhonism, triggering what Richard Popkin called the 'crisis of Pyrrhonism' — a profound intellectual upheaval that shaped the course of modern philosophy. Montaigne's Essays are saturated with Sextus. Descartes' method of radical doubt in the Meditations directly responds to Pyrrhonian arguments. Hume's skepticism about causation echoes Sextus. The entire modern epistemological project — from Descartes' quest for certainty to Kant's critical philosophy — can be understood as a sustained response to the skeptical challenge that Sextus preserved.