We review the evidence for principled processing differences between open- and closed-class morphemes and discuss a range of new evidence in the same light. The principle new evidence consists of a series of cross-modal priming experiments (Shillcock & Bard, 1993) which suggest that the perception of closed-class words strongly interacts with the syntactic processing. This is in contrast to all ambiguity resolution studies of open-class words to date, none of which has shown an influence of syntactic context. We develop the claim that the closed-class morphemes substantially embody the syntactic relations which obtain between between words in sentences. We summarize the development of formal syntactic theory over the past decade, in terms of Chomsky's Principles and Parameters model (Government and Binding Theory), and show it to be characterized by the placing of more structural responsibility onto the closed-class morphemes, bound and free. We claim that agrammatism may be captured, in formal terms, as the impairment of functional project. We present data in the form of judgments by syntacticians which demonstrate the close comparability of agrammatic language with this formal characterization.