Structure-induced equilibrium and legislative choice

In the area of legislative choice, social choice theorists have focused on the equilibrium properties of pure majority rule (PMR), operating according to the implicit belief that whatever is true about the PMR mechanism also applies to institutions based upon it. This view has encouraged the study of what seemed to be the general case, thereby avoiding the narrower study of special cases such as those that might be observed in prominent real-world legislatures, e.g., the U.S. Congress. Over the past decade, the literature has marched toward increasingly general results about the nearly complete instability of PMR; a very detailed review of these developments is found in Schofield (1980). These results in the context of the operating belief noted above seem to imply that the stability of legislative outcomes is tenuous at best. In this paper, we develop an alternative view of institutions based upon majority rule and show that PMR is a special subset of this category, if not an extreme special case. By focusing upon the manner in which institutions transform PMR into a different legislative game (such as one with a committee system), we can show the properties of legislative institutions necessary for the existence of equilibrium. The paper proceeds as follows. In Section I, we briefly review the recent literature on voting that focuses on the instability of majority rule. In Section II, we demonstrate how stability may be induced in appropriate institutional circumstances and illustrate these circumstances with several examples. In Section III, we develop the theory behind these examples, showing the general