compositionality

The concept of compositionality in semantics states that the meaning of a complex expression is determined by the meanings of its simpler constituents. Natural languages are characterized by their productivity, meaning they can generate an unlimited number of grammatical and meaningful expressions from simpler ones through various devices like concatenation and relativization.1

A compositional semantic theory explains how these complex meanings are predictable from the meanings of their parts. This contrasts with ideational semantics, which suggests meaning is purely mental and associated with ideas in an individual's mind. This view is problematic because it fails to account for the public nature of meaning, how different speakers can share and understand meanings, and crucially, it cannot explain compositionality, as an individual might associate a complex expression with an idea not derivable from its individual components.2