Williamson's Anti-Luminosity Argument
No condition is such that whenever it obtains, one knows it obtains
First published: T. Williamson, *Knowledge and Its Limits* (2000), ch. 4.
Feeling cold "luminously" means: whenever you feel cold, you know you feel cold. Williamson argues no condition is luminous in this sense.
A condition C is *luminous* iff whenever C obtains, one is in a position to know that C obtains. Williamson argues no non-trivial condition is luminous, by exploiting safety constraints on knowledge: if at very nearby times t_i and t_{i+1} you have only slightly different feelings, then if you knew C at t_i you would believe C at t_{i+1} unless you adjusted on grounds you don't have. A sorites-style argument propagates the failure across the day. The argument is the central pressure-point on Cartesian privileged access to inner states and shapes the modern debate over self-knowledge.
Formulation
Suppose condition C is luminous: ∀t (C(t) → KnowsC(t)). Consider a series of moments t_0, ..., t_n where C's strength gradually changes. Safety condition on knowledge: if Knows-C(t_i), at nearby t_{i+1} one still believes C. But adjacent moments may differ in whether C holds. Contradiction: knowledge propagates where C doesn't. Hence no luminous C.
Dimensions Engaged
Observer
Targets Observer · Knowledge Retainment: even paradigmatic inner-state knowledge has structural limits.
Information
Bears on Information · Granularity: continuous transitions defeat sharp knowledge of one's own continuous states.
Responses — How Schools Engage
Affirms / takes the bait 2
Empirically congenial: self-knowledge is mediated by error-prone cognitive processes, not by transparent introspective access.
A formal vindication of skeptical caution about even the most apparently secure knowledge claims.
Denies / rejects the premise 2
Cartesian privileged access: the mind's access to its own occurrent states is constitutive, not error-prone. The safety condition does not apply to self-knowledge.
First-person givenness of experience is not the inference-from-evidence Williamson treats it as. The argument trades on a third-person framing of self-knowledge.
Reframes the question 1
Sharpens the operational specification of "knowledge": knowledge must be safe under small perturbations of the situation, which non-trivially restricts what can be known.
Holds it inconclusive 1
A foundational argument in contemporary epistemology; defenders of privileged access have produced detailed responses (some accepting margin-of-error structure, some rejecting safety).
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Further reading
- Williamson, *Knowledge and Its Limits* (2000)
- Berker, "Luminosity Regained", *Phil. Studies* 138 (2008)
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