The term social contract describes a broad class of philosophical theories whose subject is the implied agreements by which people form nations and maintain a social order. In laymen's terms this means that the people give up some rights to a government in order to receive social order. Social contract theory provides the rationale behind the historically important notion that legitimate state authority must be derived from the consent of the governed. The starting point for most of these theories is an heuristic examination of the human condition absent any social order, termed the "state of nature" or "natural state". In this state of being, an individual's action is bound only by his or her conscience. From this common starting point, the various proponents of social contract theory attempt to explain, in different ways, why it is in an individual's rational self-interest to voluntarily subrogate the freedom of action one has under the natural state (their so called "natural rights") in order to obtain the benefits provided by the formation of social structures.
Common to all of these theories is the notion of a sovereign will which all members of a society are bound by the social contract to respect. The various flavors of social contract theory that have developed are largely differentiated by their definition of the sovereign will, be it a King (monarchy), a Council (oligarchy) or The Majority (republic or democracy). Under a theory first articulated by Plato in his Socratic dialog Crito, members within a society implicitly agree to the terms of the social contract by their choice to stay within the society. Thus implicit in most forms of social contract is that freedom of movement is a fundamental or natural right which society may not legitimately require an individual to subrogate to the sovereign will.