Scepticism

The position, or the practice, of holding that knowledge is not available - or of declining to settle whether it is.

Theme: Knowledge, truth and reason
Tradition: Greek
Term: σκέψις · skepsis
Term fixed: c. 200

In plain terms

Scepticism is not the claim that nothing is true. It is the claim - or, in its strictest form, the refusal to claim - that we are not in a position to tell.

The strategy is simple and hard to answer. For any belief, ask what supports it. Whatever is offered, ask what supports that. The chain either stops arbitrarily, circles, or runs on forever, and none of those looks like a good reason for anything. This is the same trilemma that justification faces, run in the opposite direction.

The distinction that matters is between global and local. Global scepticism doubts everything and is almost impossible to live; local scepticism doubts a particular class of claims for particular reasons, and is simply good practice. Most useful scepticism is local, and most memorable scepticism is global.

As a philosopher would put it

Pyrrhonism proceeds through the modes - the standard tropes by which any claim is met with an equally weighted opposing claim - producing suspension of judgement and, it is claimed, tranquillity. Crucially the Pyrrhonist asserts nothing, including that nothing can be known, since that would be a dogma; the Academic sceptics did make such claims, and the two ancient schools should not be run together.

The modern versions are targeted rather than global. Descartes's demon threatens the external world; Hume's problem of induction threatens all reasoning from observed to unobserved, and is the sharpest sceptical argument ever produced because it uses nothing but the premises everyone accepts.

Moore's response is to reverse the argument - he is more certain that he has hands than of any premise in a proof to the contrary, so the proof shows a premise is false. Wittgenstein's is structural: doubt needs hinges. Neither refutes the argument so much as declines it, which is roughly where the subject still stands.

Where you meet it

In 2015 the Open Science Collaboration published the results of attempting to replicate one hundred psychology studies drawn from three leading journals. Ninety-seven of the originals had reported statistically significant effects. Thirty-six of the replications did.

The project involved two hundred and seventy researchers, pre-registered protocols, and consultation with many of the original authors. Similar exercises followed in cancer biology and economics with comparable results. Nobody involved concluded that psychology is not a science, and the diagnosis that emerged was specific: small samples, flexible analysis, publication bias toward positive results.

That is scepticism working properly. It was local, aimed at a definite body of claims, motivated by a definite mechanism, and it produced changes - pre-registration, larger samples, registered reports. A global doubt about whether anything can be known would have produced nothing at all, which is the practical difference between the two kinds.

What is actually disputed

Whether scepticism can be lived, and whether it can be refuted.

The ancient objection is apraxia: a person who suspends judgement about everything cannot act, since acting requires taking something to be the case. The Pyrrhonist answer is that they follow appearances and custom without assenting to them as true, which critics have found either subtle or evasive for two thousand years.

On refutation, the record is poor. Hume's induction problem has no accepted solution; the external-world argument has been answered by declining it rather than by defeating it. What has changed is the ambition. Most contemporary epistemology treats global scepticism as a constraint to be accommodated rather than a position to be beaten, and fallibilism - accepting that any belief may be wrong while holding it anyway - is the standard settlement.

Commonly confused with

Doubt 1641 Doubt is a state. Scepticism is a position or a method built on it.
scientific scepticism That is a local practice of demanding evidence, which is compatible with holding a great many beliefs. The philosophical position is far more radical and much less useful.

Defined against

Knowledge The whole position is a denial that the relation obtains, or a refusal to say that it does

Philosophers

Pyrrho of Elis The practice, as far as it can be reconstructed
Sextus Empiricus The systematic handbook that transmitted it
René Descartes Scepticism as a method rather than a conclusion
David Hume The induction problem, and the mitigated scepticism he settled for
Al-Ghazali A sceptical crisis resolved outside philosophy
Nagarjuna A structurally similar attack from a different tradition

Works

Outlines of Pyrrhonism The primary source for the whole tradition
Meditations on First Philosophy The demon, and the attempt to answer it
A Treatise of Human Nature Induction, and the limits of reason
The Incoherence of the Philosophers Sceptical attack from within a religious tradition
Mulamadhyamakakarika The structurally similar Indian argument

Schools

Pyrrhonian skepticism Suspension as a way of life
Academic Skepticism The rival ancient school, which does assert
Cartesianism Where scepticism becomes a method
British Empiricism Where it re-emerges as a result rather than a method
Madhyamaka Buddhism The structurally similar Indian argument

Related concepts

Doubt 1641 · Knowledge c. 369 BC · Fallibility 1878 · Justification 1641 · Truth c. 330 BC

Pyrrho left no writings; Sextus Empiricus, around 200 CE, is the source for nearly everything known about the school, and his handbook is what the modern tradition actually argues with.