The argument sometimes known as the Frege-Church argument that if a context is such that co-referring singular terms (names or descriptions) can be substituted for each other salva veritate, then sentences with the same truth-value can also be so substituted. This justifies semantic theory in holding that the reference of a sentence is its truth-value rather than anything more ‘fine-grained’ such as a situation or state of affairs. The argument works by manufacturing a definite description from a sentence, and substituting a co-referring definite description with another sentence of the same truth-value in it. Suppose two propositions p, q with the same truth-value. Then from ‘p’ we derive ‘(the number x such that 2x=6 & p)=3’; substituting for the referring term in parentheses we have ‘(the number x such that 2x=6 & q)=3’ from which we derive q. The attribution to Frege, based on some remarks in ‘On Sense and Reference’, is doubtful. The slingshot has been endorsed by many logicians, although a defence against it is provided if definite descriptions are treated not as themselves being referring expressions or names, but in accordance with Russell's theory of definite descriptions.