ellauri096.html on line 204: Frederic Fitch (1963) reports that in 1945 he first learned of this proof of unknowable truths from a referee report on a manuscript he never published. Thanks to Joe Salerno’s (2009) archival research, we now know that referee was Alonzo Church.
ellauri096.html on line 206: Assume there is a true sentence of the form ‘p but p is not known’. Although this sentence is consistent, modest principles of epistemic logic imply that sentences of this form are unknowable.
ellauri096.html on line 221: is unknowable.
ellauri096.html on line 223: The cautious draw a conditional moral: If there are actual unknown truths, there are unknowable truths. After all, some philosophers will reject the antecedent because they believe there is an omniscient being.
ellauri096.html on line 229: The conclusion that there are unknowable truths is an affront to various philosophical theories, but not to common sense. If proponents (and opponents) of those theories long overlooked a simple counterexample, that is an embarrassment, not a paradox. (2000, 271)
ellauri096.html on line 233: Those who believe that the Church-Fitch result is a genuine paradox can respond to Williamson with paradoxes that accord with common sense (and science –and religious orthodoxy). For instance, common sense heartily agrees with the conclusion that something exists. But it is surprising that this can be proved without empirical premises. Since the quantifiers of standard logic (first order predicate logic with identity) have existential import, the logician can deduce that something exists from the principle that everything is identical to itself. Most philosophers balk at this simple proof because they feel that the existence of something cannot be proved by sheer logic. Likewise, many philosophers balk at the proof of unknowables because they feel that such a profound result cannot be obtained from such limited means.
ellauri096.html on line 236: Church’s referee report was composed in 1945. The timing and structure of his argument for unknowables suggests that Church may have been by inspired G. E. Moore’s (1942, 543) sentence:
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