Political theories based on the spatial model have enjoyed a dual existence. As reflected in the title of Duncan Black's (1958) famous volume, the spatial model provides a foundation for the analysis of electoral phenomena and committee decision making. It does this by providing an abstract characterization of the outcomes and preferences common to electoral and committee choice. In each setting, outcomes are represented by points in a Euclidean space. Preferences over outcomes are represented by voter (legislator) utility functions defined on points in this space. Whether an actor is called a “voter” or “legislator,” and whether a point in the space is designated a “voter's [legislator's] preferred policy,” the “policy of a candidate,” or a “legislative bill,” is little more than a labeling convention. It indicates the substantive domain of interest to the researcher.

The spatial theory of elections and the spatial theory of committees, however, have followed different paths of development as subfield-specific scholars have charted distinctive research agendas. And yet, a question pursued in one subfield – for example, is there a spatial location for a candidate that cannot be beaten by a candidate at any other location? – typically has a dual in the other subfield – for example, is there a motion that cannot be successfully amended? It is from this perspective that we explore multicandidate competition and entry in spatial models of elections. We see these phenomena as duals to agenda-setting activities in legislatures.