Living without certainty

The testimony of Aristocles, gathered from Timon, reduces all wisdom to three questions: how are things by nature, what attitude should we take toward them, and what follows from this for us. The answer to the first is what makes Pyrrho original: things are indeterminate, unstable and indiscriminable, so that neither our sensations nor our opinions tell the true or the false. From this verdict about the object, and not from an examination of our faculties, he concludes that we should place no trust in them and remain without opinion. More radical than fallibilism, which revises its beliefs, he refuses even to assert that nothing is knowable, and is content to say that things are "no more this than that".

Things are no more this than that, nor both at once, nor neither.Aristocles, cited by Eusebius, Preparation for the Gospel, XIV, 18

Aristocles (after Timon), cited by Eusebius, Preparation for the Gospel, XIV, 18 · Diogenes Laertius, Lives of the Philosophers, IX, 61-108

The skeptic observes that to every assertion an assertion of equal strength can be opposed: this is the equipollence (isostheneia) of contrary reasons. Having no means to decide, he suspends judgment (epoche), not by choice but because the unresolved conflict compels him to. Sextus systematizes this mechanism in the modes inherited from Aenesidemus and Agrippa, which drive every claim to knowledge toward infinite regress, circularity, or an arbitrary stopping point. Where Descartes would make doubt a stage toward a foundation, Sextus makes it a dwelling: no definitive certainty is attainable, and the skeptic carries caution so far as not even to assert dogmatically that there is no certainty.

To every argument an equal argument is opposed.Outlines of Pyrrhonism, I, 12

Outlines of Pyrrhonism, I, 8 and 12 · Outlines of Pyrrhonism, I, 164-169 (the five modes of Agrippa)

The problem of induction brings Hume to the edge of skepticism: if no reasoning justifies expecting the future to resemble the past, our most assured beliefs rest on custom, an instinct, not on reason. But the argument does not end in Pyrrhonian paralysis, and that is its point: nature is stronger than doubt, compelling us to believe and act the moment we leave the study. Hume therefore opposes to thoroughgoing Pyrrhonism, untenable in life, a mitigated (academical) skepticism, a moderate reserve that confines inquiry to what experience can reach.

Enquiry Concerning Human Understanding, sect. IV-V and sect. XII (of the academical or sceptical philosophy) · A Treatise of Human Nature, I, part IV, sect. 1-2

Against the Cartesian craving for indubitable foundations, Peirce erects fallibility into a principle: we can never reach absolute certainty nor perfect exactitude about anything. Yet far from sliding into skepticism, he draws from it the strength of science, which advances only by knowing itself correctable: a belief is worth holding not because it is safe from doubt, but because it belongs to a process able to detect and repair its own errors. Fallibilism is not a concession wrung from the skeptic, it is the very engine of inquiry, which would be missing in anyone who believed himself already arrived. Hence an assumed middle position, leaning slightly toward the skeptical avowal of uncertainty, yet without renouncing knowledge.

Collected Papers, I, 8-14 (Fallibilism) · The Fixation of Belief (1877)