The relationship between grammar and language behavior is not entirely clear-cut. One classic view (Chomsky 65, Bresnan & Kaplan 82, Stabler 83, Steedman 89) holds that grammars specify a time-independent body of knowledge, one that is deployed on-line by a processing mechanism. Determining the computational properties of this mechanism is thus a central problem in cognitive science. This talk demonstrates an analytical approach to this problem that divides the job up into three parts: parser = control * memory * grammar. Time-dependent sentence processing predictions then follow mechanically from the conjunction of assumptions about each of the three parts (cf. Kaplan 72). Certain combinations accord with known phenomena and suggest new experimental directions. But more broadly the approach offers an explicit, positive proposal about how human sentence comprehension works and the role grammar plays in it.