On an Argument for Truth-Functionality
ROBERT C. CUMMINS, Dale Gottlieb · 1972
A WELL-KNOWN argument of Quine's1 is ** supposed to show that any context of a sentence admitting (without change of truth value) sub? stitution of logically equivalent sentences and co? extensive individual descriptions is a truth func? tional context of that sentence. The argument is as follows. Let */>' represent any sentence, and let C(p) represent any sentence containing the sentence represented by lp It is assumed that the sentence represented by C(p) retains its truth value if (i) the sentence represented by 'p' is replaced by any sentence logically equivalent to it, or if (2) any individual description in the contained sentence is replaced by a coextensive individual description. We notice that regardless of what sentence 'p9 happens to represent, it is logically equivalent to