Gesture is typically produced with speech, forming a fully integrated system with that speech. However, under unusual circumstances, gesture can be produced completely on its own — without speech. In these instances, gesture takes over the full burden of communication usually shared by the two modalities. What happens to gesture in these two very different contexts? One possibility is that there are no differences in the forms gesture takes in these two contexts — that gesture is gesture no matter what its function. But, in fact, that’s not what is found. When gesture is produced on its own, it assumes the full burden of communication and takes on a language-like form, with sentence-level ordering rules, word-level paradigms, and grammatical categories. In contrast, when gesture is produced in conjunction with speech, it shares the burden of communication with speech and takes on a global imagistic form, often conveying information not found anywhere in speech. Gesture thus changes its form according to its function.