Skepticism

⬅️ Hub: 60.9 Philosophy · Related: Epistemology (MOC) · Foundationalism · Münchhausen trilemma - Agrippa's Trilemma

Skepticism is not one claim that “nothing can be known.” It is a family of challenges asking whether a class of beliefs has enough justification—and, in the Pyrrhonian tradition, a practice of suspending judgment when reasons appear evenly balanced.

A map of the notebook argument

Humean skepticism about induction

Induction moves from observed regularities to unobserved cases: the sun has risen each day, so it will rise tomorrow. The difficult premise is the uniformity of nature—roughly, that relevant future cases will resemble past cases.

• It is not deductively certain: a different future is logically possible.
• Defending it inductively—“induction has worked before”—uses the very method under challenge.
• Hume’s psychological diagnosis is that expectation arises through custom or habit, even if reason cannot supply a non-circular proof.

The challenge does not show that prediction is useless. It shows that ordinary predictive confidence is not grounded in deductive necessity.

Cartesian skepticism and closure

Cartesian scenarios press a different target: even vivid experience might occur while the external world is radically unlike how it appears.

The closure principle is often stated:

If I know P, and I know that P entails Q, then I can know Q.

Suppose I claim to know that I have hands. Having hands entails that I am not a handless brain in a vat. If I cannot know that I am not such a brain, closure seems to threaten the ordinary claim. Responses may reject a premise, restrict closure, argue that skeptical possibilities are irrelevant in ordinary contexts, or defend perceptual entitlement without first disproving every alternative.

Agrippa’s trilemma

When a belief is challenged, its supporting reason can appear to lead to one of three outcomes:

1. Infinite regress — every reason needs another reason without end.
2. Circularity — the chain eventually depends on the original claim.
3. Stopping point — some belief is accepted without further inferential support.

This is best treated as a map of the burden, not a one-line proof that justification is impossible.

Main families of response

Foundationalism

Some beliefs are non-inferentially justified or properly basic; other beliefs inherit justification from them. Pain experience is an intuitive candidate, but the difficult issue is whether experience justifies only a claim about one’s mental state or also a claim about the external cause.

Coherentism

A belief is justified by its role in a mutually supporting system rather than by a one-directional chain. The major objection is isolation: two internally coherent systems might fit together well while only one, or neither, tracks reality.

Infinitism

Justification can consist in an indefinitely extendable, non-repeating chain of reasons. It avoids arbitrary foundations and circles, but raises questions about finite agents who can never possess or survey the whole chain.

Epistemic entitlement or hinge commitments

Some starting commitments may be rationally unavoidable conditions of inquiry rather than conclusions proved by prior reasons. The manuscript itself labels a related view “Positism.” Because that word is clearly written on the page, it is not an OCR error; it is either the notebook’s source terminology or a nonstandard label. The underlying idea is preserved here without silently changing it to positivism or treating the label as settled terminology.

Pyrrhonism as a practice

Pyrrhonists differ from the dogmatic assertion that knowledge is impossible. Their characteristic sequence is:

1. opposed considerations reach isostheneia—rough equality of force;
2. the inquirer practices epochē—suspension of judgment;
3. tranquility or ataraxia may follow when the demand for dogmatic certainty relaxes.

This stance is itself meant to remain non-dogmatic. It keeps questioning rather than making “nothing can be known” into one more doctrine.

A disciplined practical stance

The useful middle position is neither gullibility nor performative doubt:

• scale confidence to the quality of evidence;
• distinguish certainty, knowledge, reasonable belief, and useful working assumption;
• name the skeptical alternative that actually matters;
• ask what observation would discriminate between live explanations;
• suspend judgment when the evidence does not warrant a verdict, but do not confuse absence of certainty with absence of reason.

Handwritten Notebook Pages

Source

• Open Skepticism notebook pages — start at notebook p. 29 (file not included in this release)
• Open Skepticism notebook pages — start at notebook p. 60 (file not included in this release)

Retrieval questions

• Why can induction not be justified by saying that it has worked before?
• How does closure generate the brain-in-a-vat problem?
• What are the three horns of Agrippa’s trilemma?
• How do Pyrrhonists differ from people who assert that knowledge is impossible?
• Which objection most directly pressures coherentism?