Skepticism is the Pyrrhonian discipline of suspending judgment: for every argument an equal argument stands opposed, and the skeptic, ceasing to dogmatize, finds the tranquility that eluded the believers.
Skepticism as a school descends from Pyrrho of Elis, who traveled with Alexander to India and returned teaching indifference to appearances' disputes. Preserved by Sextus Empiricus, whose Outlines of Pyrrhonism is the school's surviving handbook, it resurfaced in the Renaissance to trouble a dogmatic age — Montaigne took its motto, 'What do I know?', and modern philosophy begins in Descartes's attempt to answer it.
Ultimate Reality
The skeptic makes no claim about ultimate reality: things in their real nature are, for all we can establish, indeterminable. This is not the dogma that nothing can be known — that too would be a claim — but a report of the inquirer's position: opposed accounts balance (isostheneia), and where they balance, judgment suspends itself (epoche).
The Human Condition
The human trouble is disturbance (tarache) produced by belief: those who hold that things are good or bad by nature suffer twice, from the thing and from the opinion. The skeptic began, like everyone, seeking tranquility through truth, and found it instead as a byproduct — as Apelles, flinging his sponge at the painting in frustration, achieved the horse's foam he could not paint on purpose.
Knowledge and Truth
The skeptic lives by appearances (phainomena) without assenting to them as truths: the fourfold observance of ordinary life — nature's guidance, the feelings' compulsion, custom and law, and the arts — suffices for action. The Ten Modes of Aenesidemus and the Five Modes of Agrippa are the school's instruments, regress, circularity, and hypothesis among them, still recognizable in every modern critique of foundations.
Right and Wrong
Following appearances, the skeptic conforms outwardly to the customs and laws of their place, worshipping with the city and eating with the household, while inwardly withholding the assent that makes customs into torments. Moderation in feeling (metriopatheia) replaces the sage's impossible impassivity: the skeptic is cold when cold comes, but does not add the opinion that cold is evil.
Human Destiny
Skepticism promises no destiny beyond the tranquility available in this life to the one who stops demanding that reality sign its name. Death, the afterlife, and providence fall under the same suspension as everything else non-evident; the skeptic neither affirms nor fears them, and reports the resulting quiet as the school's whole eschatology.
The Conversation
Skepticism asks every system the question it cannot enjoy: by what criterion is your criterion certified, and who certified the certifier? The systems answer with the self-refutation charge — that the skeptic dogmatizes about doubt — and Sextus's school replies that its phrases purge themselves along with the rest, like a medicine that expels itself with the disease.