Skepticism

Any claim to know the hidden nature of things presupposes a criterion of the true; yet that criterion would itself need validating by another, and so on without end, or else guarantee itself, which begs the question. The skeptic therefore does not assert that nothing is knowable, which would still be a dogmatic thesis: he observes that for every proof advanced a contrary proof of equal force stands (the isostheneia), and that this unresolved conflict forces epochē. What sets him apart from dogmatists and Academics alike is that he concludes neither to knowledge nor to ignorance: he keeps inquiring, without closing the matter.

Sextus Empiricus, Outlines of Pyrrhonism, I, 8-10 · Diogenes Laertius, Lives, IX, 78-79

To name is to carve reality into opposed categories (great and small, true and false), yet the dao 道 (the Way) is the undivided ground from which those distinctions proceed: no word can grasp it without betraying it. Language fits bounded things, never the source that engenders them all. Zhuangzi draws from this a radical perspectivism: every judgment speaks from a situated standpoint, disputation merely sets two partialities against each other with no judge above them, and to claim a universal verdict is to mistake one's perch for the center of the world. Hence a skepticism that aims less to deny than to dissolve the claim to certain knowledge and to free one from the need to be right.

Laozi, Dao De Jing, ch. 1 · Zhuangzi, ch. 2 (On the Equality of Things)

No belief rests on a first, indubitable foundation: it is the error of dogmatism, and of Cartesian doubt, to seek outside inquiry a bedrock that would secure it from without. Peirce reverses the order: one never starts from scratch but from a fabric of inherited beliefs that only a real doubt, sprung from a concrete difficulty, can unsettle, never a feigned doubt posited on principle. Hence fallibilism: our best-assured opinions stay correctable by future experience, none escaping revision by right. The position thereby parts company both with the rationalist quest for a certain starting point and with the skepticism that, lacking such a point, would suspend action: one inquires from within revisable beliefs, with no outside to ground them.

Peirce, 'The Fixation of Belief' (1877) · Dewey, Logic: The Theory of Inquiry (1938)

Drawing all knowledge from experience forces one to accept its precariousness: what comes only from the senses cannot carry the necessity of a demonstration. Locke therefore confines certain knowledge to a narrow domain and files the rest under mere probability, and Hume strikes the decisive blow by showing that matters of fact rest on induction, which presupposes without being able to prove that the future will resemble the past. This lucidity about the limits of understanding sets the school against the rationalist claim to a complete deductive system, yet without lapsing into radical doubt: its skepticism stays mitigated, corrective rather than destructive.

Locke, Essay Concerning Human Understanding, book IV · Hume, Enquiry Concerning Human Understanding, sections IV and XII

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".

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.

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

The motto "What do I know?" is not a thesis but a question held open. In the Apology for Raymond Sebond, Montaigne takes up the whole arsenal of the Greek skeptics, the diversity of opinions, the weakness of the senses, reason's dependence on custom, to humble the pride of a reason that claims to ground everything. But his skepticism does not stop at Pyrrho: he refuses systematic epochē as a new dogma, keeps the use of beliefs in order to live, and turns doubt not toward an impassive ataraxia but toward modesty, self-inquiry and tolerance. It is an inhabited, fallibilist-before-the-word doubt, the goad from which Descartes, against him, would make his starting point.

Essays, II, 12, "Apology for Raymond Sebond"

There is no view from nowhere: all knowledge is the optics of a will, an interpretation in the service of some vital interest. The ideal of an « objective », disinterested truth is itself a value, and a rather life-hostile one. Yet this perspectivism is no flat relativism: perspectives can be ranked by their fruitfulness, and it is by multiplying viewpoints that one gains in « objectivity ».

Posthumous Fragments, autumn 1885-1886, 7[60] · Beyond Good and Evil, §34

Every judgment is made from a standpoint, and each standpoint has its "this" and its "that": what one party holds true the other holds false, and no neutral tribunal can settle them without itself being a party. Zhuangzi draws from this a scepticism about discursive knowledge: the controversies of the Confucians and the Mohists cancel out, dream cannot be securely told from waking, and one does not even know whether one knows anything. Yet this doubt is not the Greek suspension aimed at tranquillity: it is therapeutic and liberating, dissolving the anxiety of having to be right so as to leave room for a supple knowing attuned to the course of things.

Zhuangzi, ch. 2 (On the Equality of Things) · Zhuangzi, ch. 2 (the butterfly dream)

To silence an opinion presupposes that one knows it false, hence that one believes oneself infallible: yet no one is, and history is full of truths first persecuted. From this fallibility Mill draws the demand for debate: suppressing an opinion may rob us of a truth, and even a false one sharpens, by contradiction, the received truth, which without it decays into a dead dogma professed without grasp of its meaning. Doubt for him is thus no paralysing scepticism but the condition of living knowledge, which ranks him, without surrendering truth, on the side of fallibilism.

On Liberty, ch. 2 (the argument from fallibility and the dead dogma)

The human mind demands unity, clarity, ultimate certainties; the world answers with an unreasonable silence. From this divorce springs the absurd: the absolute truths reason craves lie beyond its reach, and any thought that promises them, religious or systematic, performs a leap away from the evidence. Yet Camus guards against wholesale skepticism, which refutes itself in asserting itself: at least two things remain certain, the absurd itself and the bare fact of existing. Lucidity holds to this middle ground, refusing both metaphysical hope and the surrender of knowing.

The Myth of Sisyphus, An Absurd Reasoning

After the Delphic oracle declared no one wiser than he, Socrates, convinced he knew nothing, set out to refute the god, and found that men reputed wise knew no more than he but believed they did. His superiority lies wholly in not imagining he knows what he does not: this learned ignorance is no skepticism that gives up on truth, but the mainspring of the elenchus, which dissolves false certainties to reopen the inquiry.

Plato, Apology, 20e-23b (the oracle and the inquiry)

"The Dao that can be named is not the constant Dao": ultimate reality eludes language and concepts, which carve up and fix what is fluid. Laozi mocks busy knowledge and exalts a "knowing not-knowing," but this is not the skepticism of suspended judgment: it is a higher, intuitive and silent knowledge, attuned to the Dao. The doubt bears on discursive knowledge, not on access to truth, hence a median position leaning toward distrust.

Dao De Jing, ch. 1 and 56 · Dao De Jing, ch. 48 and 71

Locke bounds the understanding: certain, demonstrative knowledge is rare, confined to mathematics and a few moral or metaphysical truths. About existing things and matters of fact we have only probable knowledge, resting on experience and testimony. Without lapsing into skepticism, he urges a measured distrust of our claims to certainty.

Essay Concerning Human Understanding, IV, ch. 2-3 (degrees and extent of knowledge) and ch. 15-16 (probability)