Intensionalité

Intensionalité refers to a concept in logic and linguistics concerning the meaning or sense of linguistic expressions, particularly propositions and predicates. It contrasts with extensionality, which focuses on the set of things an expression refers to. An intensional approach considers not just what is true or false, but how it is true or false, or the conditions under which it is true or false.

For example, the proposition "The morning star is visible" and "The evening star is visible" might be considered extensionally equivalent if the morning star and the evening star are indeed the same celestial body. However, intensionally, they are distinct. Their truth depends on different conceptual contents or ways of thinking about the object. Intensionality is concerned with the meaning, understanding, or conceptual role of an expression, rather than its reference in the real world.

In modal logic, intensional contexts, such as those involving necessity and possibility, are crucial. If a statement is necessarily true, it is true in all possible worlds. This necessity is an intensional property, not merely an extensional one. The meaning of a sentence can be thought of as the set of conditions under which it is true, or the way it represents a state of affairs. This focus on meaning and conceptual content is the essence of intensionalité.