compositionality

Compositionality is a principle in semantics and formal linguistics stating that the meaning of a complex expression is determined by the meanings of its parts and the way those parts are syntactically combined. It is closely associated with the idea that meanings are built up from smaller pieces in a systematic way, so that knowing the parts and the structure suffices to determine the whole.

In linguistics, compositionality underpins many formal theories of meaning, such as Montague semantics and categorial grammar. A canonical claim is that the semantic value of a sentence can be computed by function application to the semantic values of its constituents. For example, the sentence “John loves Mary” is interpreted as the application of the love relation to the two individuals, yielding a truth-conditional meaning. This framework also handles modifiers, quantifiers, and other functional expressions through higher-order functions and lambda abstraction.

In computer science, compositionality guides the design of programming language semantics. Denotational and operational approaches seek to assign meanings to programs in a way that preserves structure: the meaning of a compound construct is determined by the meanings of its parts and the rules of combination. This enables modular reasoning, program transformation, and formal verification.

Limitations and challenges include idioms, context-dependent expressions, and certain use-theory phenomena where literal compositional analysis fails. Extensions such as dynamic semantics, presupposition theory, and context-sensitive approaches broaden the scope beyond strict compositionality. Despite limitations, the principle remains a foundational tool for systematic analysis of meaning.