The determination of content

I identify a notion of compositionality at the intersection of the different notions philosophers, linguists, and psychologists are concerned with. The notion is compositionality of expression content: the idea that the content of a complex expression in a context of its utterance is determined by its syntactic structure and the contents of its constituents in the contexts of their respective utterances. Traditional arguments from productivity and systematicity cannot establish that the contents of linguistic expressions are compositionally determined in this sense. I present a novel argument for this thesis.