A term or denoting expression (e.g., name, description) has two distinct linguistic components:
- Extension: the reference, or what the thing refers to. The extension of a predicate is the set of things it applies to; the extension of a sentence is its truth value.
- Intension: the internal semantic meaning of the term that determines its extension.
A famous example is Frege’s “morning star” and “evening star.” These terms designate the same object, Venus, but have different meanings.