The Source of Intensionality

Abstract

In (1) we can replace Dean by any other coextensional term and preserve truth value; also, from (1) we can infer that there is someone Mary is talking to. Such behavior breaks down in (2): neither intersubstitution of coextensional terms nor existential generalization guarantee preservation of truth value in a sentence like (2). (1) is purely extensional; (2) is intensional. The typical examples of intensional contexts are sentences subordinated to modal operators or to verbs of propositional attitude. It is quite common to refer to expressions like it is necessary, it might have been the case, believes, wishes, etc., as intensional operators. In fact, the notion of intensional context has been used in semantics in two different ways. On the one hand, contexts that are embedded under the scope of a modal operator or a verb of propositional attitude are classified as intensional. But, in general, any context that exhibits a failure of substitutivity or a failure of existential generalization is classified as intensional. The underlying assumption behind the liberal use of these two modes of classification is that they both amount to the same thing, namely, that the so called intensional operators are the cause of the failure of substitutivity and existential generalization. The purely extensional behavior of sentences like Cicero was a Roman orator or number of planets is greater than seven is altered when, and because, those sentences are embedded under the scope of certain expressions that create an intensional environment. The underlying assumption, in other words, is that embedding (under the scope of a modal operator or a verb of propositional attitude) is the cause and the source of