A Grammar of Projections

A sequence of nodes in a syntax tree, each the head of the next, is usually called a projection path, or simply a projection. Projections in this sense are fairly basic phrase-structural entities, though hardly of central importance in most accounts. There are a few exceptions. For example, varieties of projection that I called c-projection and s-projection were significant in my earlier work on the grammar of function words, and the distinction was further developed by Grimshaw under the rubric extended projections. And in quite a different direction, Kayne proposed g-projections to account for constraints on long-distance dependencies. Pesetsky, inspired by Kayne’s g-projections, proposed using paths as the basis for an account of locality; and his paths, in turn, are reminiscent of the feature-passing paths that figure prominently in intuitive accounts of attribute-value grammars. If there is more to this train of precedent than just free association and coincidences of terminology, it suggests that an account of both constituent structure and long-distance dependencies might be based on a single notion of projection. I would like to propose such an approach in the present work. As a point of departure, let me make another set of free associations, not obviously related to the first. Traditionally, there have been two broad approaches to phrase structure: immediate-constituent analysis and dependency analysis. American structuralists mostly assumed immediate-constituent analysis in preference to dependency analysis, and that prejudice was inherited by Chomsky and transformational grammar. But as transformational grammar has evolved, it has assigned an ever more central role to dependency concepts. Whereas dominance is the primitive structural relation in immediate-constituent analysis, government is the fundamental structural relation in dependency grammar. At least since the point at which the Extended Standard Theory evolved into Government-Binding Theory (GB), government has come to play a central role in Chomsky’s work. (Some related notions had a prominent place in the theory much earlier, including headship and command—the latter being definable as the transitive closure of government.) I think it is not far from the mark to say that GB reconstructs dependency structures as defined terms, atop an immediate-constituency substrate. And with the more recent introduction of ‘bare phrase structure’ [?], Chomsky’s phrase structures have all but abandoned the immediate-constituent substrate, and become nearly pure, if somewhat idiosyncratic, dependency stemmas. But let us return now to the relation between dependency structure and constituent structure, and the question of what it has to do with projections. There is something rather unsatisfying about the opportunistic mixture of constituent structure and dependency structure in GB. Constituent grammars (i.e.,