 Natural language is   compositional: complex  linguistic expressions are built from simpler linguistic expressions, and the meaning of a complex expression is a function of the meanings of its constituents together with the way those constituents are combined. Compositional semantics describes in a systematic way how semantic properties of a complex expression depend upon semantic properties of its constituents and the way those constituents are combined. For example, the truth-condition of a conjunction is determined as follows: the conjunction is true iff both conjuncts are true.