We examined temporarily ambiguous coordination structures such as "put the butter in the bowl and the pan on the towel." Minimal Attachment predicts that the ambiguous noun phrase "the pan" will be interpreted as a noun-phrase coordination structure because it is syntactically simpler than clausal coordination. Constraint-based theories assume that interpretations are the result of a constraint-satisfaction process, which predicts that frequency or context can bias the parser to initially pursue a more complex interpretation. The results showed an initial preference for noun-phrase coordination, despite the fact that sentential coordination is more frequent in imperative structures. These data suggest that the parser uses a syntactic simplicity heuristic for building initial structural analyses. (Contains 7 figures, 3 tables, and 2 notes.)