Combinatory Categorial Grammar (CCG) was originally advanced as a theory relating coordination and relativization. The claim was that these constructions can be analysed at the level of surface grammar, without rules of movement, deletion, passing of slash-features, or the syntactic empty category Wh-trace. Instead, CCG generalizes the notion of grammatical constituency to cover everything that can coordinate or result from extraction, via the use of a small number of operations which apply to adjacent lexically realised grammatical categories interpreted as functions.