 Compositionality is the principle that the meaning or content of a complex expression is a function of the meanings of its constituent expressions. It’s commonly taken to be a mandatory feature of any adequate theory of meaning and content. The argument is that, as competent speakers of a language, we are in principle capable of grasping the meanings of a potentially infinite number of sentences. And since we’ve learnt the meanings of a limited number of words, this is possible only if the meanings of complex sentences are obtainable recursively from the meanings of their constituent parts (Davidson 1965). 