A little history, to begin with: the phenomena that come under the heading ‘English auxiliaries’ were instrumental in bringing about the contemporary era in syntax, and, beyond syntax, in linguistics as a field. In Chomsky's watershed 1957 monograph Syntactic Structures, these phenomena were perhaps the key setpiece for the pivotal argument in the book that context-free phrase structure rules, of the sort that we first formulated to capture basic phrasal constituency in English, get crucial facts about the language wrong. Chomsky's point was not that such rules cannot summarize our observations about what we find in English, but rather that, implicitly, they deny the existence of a certain kind of pattern that can in fact be shown to exist, and therefore are wrong, not about the data, but about recurrent patterns in the data. The new kind of rule that Chomsky proposed to deal with this difficulty (a more user-friendly version of a kind of mechanism that certain logicians and linguists of the preceding generation (in particular Emil Post and Zelig Harris) had devised and experimented with) had the apparent virtue of being able to express these patterns easily. A good deal of the development syntax has experienced in the last quarter of a century reflects a somewhat belated counting of the costs incurred by Chomsky's innovation, and a gradual realization that there were far simpler, more economical solutions to the problem he pointed out with empirical coverage considerably better than what he had proposed in 1957.

The particular virtue of Chomsky's approach, then, is not the particular solution he advanced, which has become progressively less attractive as time has passed (even independently of framework-internal changes in the specific theory he inaugurated), but rather the enhanced scope of the linguist's intellectual responsibilities that it assumed. Recording the facts correctly no longer had the status of a sufficient activity, even with a convenient classification and organization of those facts; what was now essential was motivating those facts, by showing how they were manifestations of underlying patterns and their interaction. One could characterize most previous work in linguistics as at best proto-scientific, in the sense that recording and classification are crucial to the actual business of science, but are not themselves that business, which is to identify a domain of phenomena and discover the general principles governing the behavior of the phenomena in that domain.