Broken agreement.

The subjects and verbs of English sentences agree in number. This superficially simple syntactic operation is regularly implemented by speakers, but occasionally derails in sentences such as The cost of the improvements have not yet been estimated. We examined whether the incidence of such errors was related to the presence of subject-like semantic features in the immediate preverbal nouns, in light of current questions about the semantic versus syntactic nature of sentence subjects and the interactivity of language processing. In three experiments, speakers completed sentence fragments designed to elicit erroneous agreement. We varied the number and animacy of the head noun and the immediate preverbal (local) noun, as well as the amount of material separating the head noun from the verb. The plurality of the local noun phrase had a large and reliable effect on the incidence of agreement errors, but neither its animacy nor its length affected their occurrence. The latter findings suggest, respectively, that the semantic features of sentence subjects are of minimal relevance to the syntactic and morphological processes that implement agreement, and that agreement features are specified at a point in processing where the eventual length of sentential constituents has little effect on syntactic planning. Both results follow naturally from explanations of language production that emphasize the segregation of sentence formulation processes into relatively autonomous components.