Against the Dogmatists

Before anyone can claim to know, there must be some way to tell a true impression from a false one. The two books against the logicians ask whether any such test exists, and find every candidate disputed.

The logical books open with a survey of what philosophers from Xenophanes to Carneades proposed as the judge of truth: reason, the senses, both, or the human being who uses them. Sextus spends longest on the Stoic answer, an impression stamped by its object so exactly that it could not have come from anything else. The stories told in its defence undo it, from Menelaus disbelieving the real Helen to Orestes seeing his sister as a Fury. Disputed tests cannot settle disputes, so judgment is suspended.

• epistemology
• perception
• truth
• knowledge
• mental representation
• stoicism
• reason

Can we reason from what we see to what we cannot, from sweat to hidden pores, from premises to a hidden truth? The second book against the logicians weighs every argument for doing so against an equal one.

Sextus separates two kinds of sign. Smoke recalls fire because the two have been seen together, and such reminders he leaves to everyday life, which the skeptic does not fight. His quarrel is with signs said to reveal what is hidden by nature, like the pores physicians inferred from sweat, and with proof, a sign of that kind. Both take the form 'if this, then that', so the unsettled dispute between Philo and Diodorus over such sentences reaches them too.

• signs
• demonstration
• inference
• logic
• argumentation
• evidence
• definition

Where did belief in gods come from, and can argument settle whether they exist? The first book against the physicists gathers the answers of believers and doubters and lets them cancel out.

Sextus first collects accounts of how people came to think of gods: that they deified the sun and rivers that fed them, or powerful rulers, or that lawgivers invented an all-seeing god to deter secret crimes. Then come the arguments for gods, from the agreement of all peoples and the order of the world, and those against, among them Carneades' puzzles about a god with every virtue. In practice the skeptic follows his country's custom, says there are gods and worships them, while committing himself to nothing in philosophical inquiry.

• theology
• cosmology
• existence
• skepticism

Do the things physics takes for granted, causes, bodies, motion, place, time and number, survive close questioning? The books against the physicists take each apart until it is no clearer than its opposite.

Sextus works through the building blocks of nature one at a time. A cause that precedes its effect is not yet a cause, and one that arrives with it has no better title than the effect. Nothing can move where it is, nor where it is not, as the logician Diodorus argued. Past time is gone, future time is not yet, and the present has no length. Each argument is set against the physicists' own, so that judgment is suspended rather than motion or time denied.

• causation
• motion
• time
• body
• change
• place
• number
• geometry
• metaphysics

If nothing is good or bad by nature, what is left to pursue, and would we be calmer for knowing it? The book against the ethicists argues that belief in natural goods is itself the source of trouble.

Fire warms everyone who comes near it, but no supposed good, whether pleasure, wealth, health or virtue, pleases everyone alike, so Sextus finds nothing good by nature. A person convinced that wealth is such a good suffers while pursuing it and again while guarding it, and the teacher who swaps that craving for a craving for virtue cures pleurisy by causing pneumonia. Nor, he argues, can an art of living be taught. Some scholars find this book closer to asserting its conclusion than suspended judgment strictly allows.

• ethics
• value theory
• virtue