Colin Phillips and Shevaun Lewis
Standard generative grammars describe language in terms that appear distant from considerations of everyday, real‐time language processes. To some this is a critical flaw, while to others this is a clear virtue. One type of generative grammar defines a well‐formed sentence as a static, structured representation that simultaneously satisfies all relevant constraints of the language, with no regard to how the representation is assembled (e.g., Sag, Wasow, & Bender, 2003). Another type of generative grammar defines a well‐formed sentence as a derivation, or sequence of representations, that describes how the sentence is gradually assembled, often including various transformations that move words or phrases from one position to another in a structure. In the most popular current version of the derivational approach, derivations proceed ‘upwards’, starting from the most deeply embedded terminal elements in the sentence, which are often towards the right of a sentence (e.g., Chomsky, 1995; Carnie, 2006). Such derivations tend to proceed in a right‐to‐left order, which is probably the opposite of the order in which sentences are assembled in everyday tasks such as speaking and understanding. Since these theories make no claim to being accounts of such everyday processes, the discrepancy causes little concern among the theories' creators. Generative grammars are typically framed as theories of speakers’ task‐independent knowledge of their language, and these are understood to be distinct from theories of how specific communicative tasks might put that knowledge to use.
Set against this background are a number of recent proposals that various linguistic phenomena can be better understood in terms of derivations that incrementally assemble structures in a (roughly) left‐to‐right order. One can evaluate these proposals based simply on how well they capture the acceptability judgments that they aim to explain, i.e., standard conditions of 'descriptive adequacy'. But it is hard to avoid the question of whether it is mere coincidence that left‐to‐right derivations track the order in which sentences are spoken and understood. It is also natural to ask how left‐to‐right derivations impact the psychological commitments of grammatical theories. Are they procedural descriptions of how speakers put together sentences in real time (either in comprehension or in production)? Do they amount to a retreat from linguists’ traditional agnosticism about ‘performance mechanisms’? These are questions about what a grammatical theory is a theory of, and they are the proverbial elephant in the room in discussions of left‐to‐right derivations in syntax, although the issues have not been explored in much detail. Here we summarize the current state of some of the evidence for left‐to‐right derivations in syntax, and how this relates to a number of findings by our group and others on the nature of real‐time structure building mechanisms. Some of these questions have been aired in previous work (e.g., Phillips 1996, 2004), but we have come to believe that the slogan from that earlier work (“the parser is the grammar”) is misleading in a number of respects, and we offer an updated position here.