 Anything that deserves to be called a language must contain meaningful expressions built up from other meaningful expressions. How are their complexity and meaning related? The traditional view is that the relationship is fairly tight: the meaning of a complex expression is fully determined by its structure and the meanings of its constituents—once we fix what the parts mean and how they are put together we have no more leeway regarding the meaning of the whole. This is the principle of compositionality, a fundamental presupposition of most contemporary work in semantics.