To what extent are the grammatical conventions of human languages shaped by performance? In particular, can rules and principles of the syntax be explained by considerations of processing, and by the temporal sequencing of speech? There has been some discussion of this question in the past, among linguists and psychologists, and the consensus seems to be: only to a limited extent. That is, processing may nibble at the edges of the grammar but does not appear to be a major determinant of syntactic conventions.

I believe that this consensus is mistaken. It comes from looking at insufficient data from too few languages, and from accepting too uncritically certain common assumptions in theories of grammar and in theories of performance. When we expand the data and the language sample, and pursue other theoretical assumptions, we reach a very different conclusion: namely, that grammars are profoundly shaped by processing. I believe that even highly abstract and fundamental properties of syntax can be derived from simple principles of processing that are needed anyway, in order to explain how language is used.

This conclusion has been reached after a close analysis of linear ordering in performance and in grammars. It is further motivated by the correspondences between on-line procedures for recognizing constituent structure and the grammatical devices that make such recognition possible. It is also supported by grammatical constraints on relativization, on movement, and on various other phenomena across languages. As a result, performance now joins the core of an explanatory model of syntax.