Speech is produced incrementally. The Incremental Parallel Formulator (De Smedt, 1996) is a computational model of grammatical encoding that takes this notion of incrementality into account. It predicts that the order and time-scale with which conceptual fragments activate lexical segments affect the syntactic shape of an utterance. We derived predictions firom this model and tested these in two online experiments. In these experiments, participants described computer animations in which two objects moved in upward or downward directions. We manipulated the availability of pieces of the conceptual input by withholding either the information about the movement direction, or about the identity of one of the objects for various amounts of time. The experiments showed that both the type and the temporal availability of conceptual information strongly affect the syntactic shape of an utterance.