"Social contract" is the name given to a group of related and overlapping concepts and traditions in political theory. Like other such aggregations in philosophy and intellectual history, it has at its center an extremely simple conceptual model, in this case that the collectivity is an agreement between the individuals who make it up. This model suggests that it is proper to ask whether the agreement was or is voluntary in character and whether, therefore, the individual can decide to withdraw either because he no longer agrees or because the conditions that are or were understood in the agreement are not being maintained. It suggests furthermore that the individual should be thought of as logically prior to the state or to society, and that it is meaningful to speculate on situations in which individuals existed but no collectivity was in being. From a historical point of...