Editing Fitch's paradox of knowability (section)

{{More footnotes needed|date=April 2024}}
'''Fitch's paradox of knowability''' is a puzzle of [[epistemic logic]]. It provides a challenge to the ''knowability thesis'', which states that every truth is, in principle, knowable. The [[paradox]] states that this assumption implies the ''omniscience principle'', which asserts that every truth is known. Essentially, Fitch's paradox asserts that the existence of an unknown truth is unknowable. So if all truths were knowable, it would follow that all truths are in fact known.

The paradox is of concern for [[verificationist]] or [[anti-realist]] accounts of truth, for which the ''knowability thesis'' is very plausible,<ref>{{Cite book|url=http://philpapers.org/rec/MLLETO|title=Epistemic theories of truth: The justifiability paradox investigated|date=1996|last=Müller|first=Vincent C. W.|author2=Stein, Christian|pages=95–104 |publisher=Universidade de Santiago de Compostela }}</ref> but the omniscience principle is very implausible.

The paradox appeared as a minor [[theorem]] in a 1963 paper by [[Frederic Brenton Fitch|Frederic Fitch]], "A Logical Analysis of Some Value Concepts". Other than the knowability thesis, his proof makes only modest assumptions on the [[modal operator|modal]] nature of [[knowledge]] and of [[subjunctive possibility|possibility]]. He also generalised the proof to different modalities. It resurfaced in 1979 when [[W. D. Hart]] wrote that Fitch's proof was an "unjustly neglected logical gem".