The principle of compositionality is the claim that the meaning of a complex expression is determined by its structure and the meanings of its constituents. Normally the thesis is taken to be about some particular language; questions of structure and constituency are then settled by the syntax of that language. By extension, we can talk about compositionality in other representational systems—thoughts, traffic signs, musical notation, and so on—as long as they have their own syntax.

Varieties of Compositionality

The principle is not committed to a specific conception of syntax and semantics, which is why it can be employed in debates between proponents of different conceptions (see, by way of comparison, Partee 1984). Still, if we reject all constraints on either structure or meaning, compositionality becomes trivial. As T. M. V. Janssen (1986) has shown, we can turn any meaning function on a recursively enumerable set of expressions into...