Abstract

The semantic puzzles posed by propositional attitude contexts have, since Frege, been understood primarily in terms of certain substitution puzzles. We will take as paradigmatic of such substitution puzzles cases in which two coreferential proper names cannot be intersubstituted salva veritate in the context of an attitude verb. Thus, for example, the following sentences differ in truth value: (1) Lois Lane believes Superman can fly. (2) Lois Lane believes Clark Kent can fly. despite the fact that "Superman" and "Clark Kent" pick out the same individual.1 Equivalently, the following sentence may be true: (3) Lois Lane believes that Superman can fly, but that Clark Kent cannot fly. despite the coreferentiality of the names. (It will at times be convenient to appeal to this conjunctive attitude report in order to fix a single context of utterance.) Substitution failures such as these create a puzzle when conjoined with the assumptions (a) that attitude reports report a binary relation between an individual and some object of that individual's attitude and (b) that that object of the attitude is determined by the content of the complement sentence in the attitude report. If all of the terms in two complement sentences (e.g., "Superman can fly" and "Clark Kent can fly") have the same semantic content, then, prima facie, they ought to generate the same object of believe and, a fortiori, materially equivalent attitude reports. Frege, famously, attempts to defuse the puzzle by positing a semantic value of sense in addition to that of reference, and thereby distinguishing the semantic contents of the two complement sentences.