||The principle of semantic compositionality (PC) says, in a standard formulation: "The meaning of a complex expression is a function of the meanings of its parts and its mode of composition." It is a guiding principle in most of formal semantics. In the philosophy of language, as well as in linguistics more generally, it is controversial. Some think it is trivially true, or even empirically empty. Others think it is false (e.g. because of quotation, or belief sentences, or idioms). Yet others think it is true, or approximately true, and that it has explanatory value. Intuitions anticipating (PC) were expressed already in medieval times, but it was not stated in its modern form until the early 1980s.