Combinatory categorial grammar

In formal linguistics, combinatory categorial grammar (CCG) is an efficiently parsable, yet linguistically expressive, grammar formalism. It has a transparent interface between surface syntax and underlying semantic representation, including predicate–argument structure, quantification, and information structure. The formalism generates constituency-based structures (as opposed to dependency-based ones) and is therefore a type of phrase structure grammar (as opposed to a dependency grammar).

CCG relies on combinatory logic, which has the same expressive power as the lambda calculus, but builds its expressions differently. The first linguistic and psycholinguistic arguments for basing a grammar on combinators were put forth by Steedman and Szabolcsi.

More recent prominent proponents of CCG include Pauline Jacobson and Jason Baldridge, who have continued development therein. In these new approaches, the combinator B (the "compositor") is found to be useful in creating long-distance dependencies—as in, e.g., "Who do you think Mary is talking about?"—and the combinator W (the "duplicator") is useful for the lexical interpretation of reflexive pronouns, as in "Mary talks about herself". Together with I (the identity mapping) and C (the "permutator"), these form a set of primitive, non-interdefinable combinators. Jacobson interprets personal pronouns as the combinator I; their binding is aided by a complex combinator Z, as in "Mary lost her way". Z is definable using W and B.