Intension and Extension
Intension and Extension describe two ways of indicating the meaning of a word or name. Intension assumes the word has an intrinsic meaning, perhaps simply by definition and thus "analytic." Extension is the set of objects in the world to which the word corresponds. There is a special kind of definition called "ostensive" which defines a word by pointing to those objects. Because extension involves things in the world it is called "synthetic." The mathematician Gottlob Frege distinguished intension and extension by the German words Sinn and Bedeutung (which translate usually as Sense and Meaning). Most logicians follow Frege’s distinction between the reference (denotation, name) and the sense (meaning) of a word. But few know that Frege limited the “sense” to the everyday meaning attached to a word by the users of the language. Frege also described the “idea” or “representation” (Vorstellung) that would form in the mind of the message receiver. This, he said, would be different in every mind, since it is dependent on the peculiar experiences of each person.
This fits perfectly with our experience recorder and reproducer (ERR) as a model of mind, memory, and knowledge. Vienna Circle philosophers, notably Rudolf Carnap described intension and extension as semantisch and pragmatisch (semantic and pragmatic). The idea that meaning is "semantic" captures perfectly the post-modern idea that words are trapped in a "circle of signifiers" and Derridean deconstruction. It is the fundamental ambiguity of words that makes them unacceptable as the basis for philosophy and science. We need to go "beyond language and logic." Willard van Orman Quine used the terms Meaning and Reference for intension and extension. Note the rough correlation between a priori and a posteriori and the ideas of intension and extension. Intensions are theoretical, "ideas" in minds." Extensions attempt to represent empirically what is "out there" in the external world. Thus intension/extension can thus be seen to be part of the "great dualism."