Every account of communication involves assumptions about action, in particular about the bases for action's coherence and intelligibility. This chapter and the next discuss two alternative views of action. The first, adopted by most researchers in artificial intelligence. locates the organization and significance of human action in underlying plans. At least as old as the Occidental hills, this view of purposeful action is the basis for traditional philosophies of rational action and for much of the behavioral sciences. It is hardly surprising, therefore, that it should be embraced by those newer fields concerned with intelligent artifacts. particularly cognitive science and information-processing psychology. On the planning view, plans are prerequisite to and prescribe action, at every level of detail. Mutual intelligibility is a matter of the reciprocal recognizability of our plans, enabled by common conventions for the expression of intent and shared knowledge about typical situations and appropriate actions. The alternative view, developed in Chapter 6 of this book, is that although the course of action can always be projected or reconstructed in terms of prior intentions and typical situations, the prescriptive significance of intentions for situated action is inherently vague.