Legitimacy
Legitimacy is the right and acceptance of an authority, usually a governing law or a regime. Whereas authority denotes a specific position in an established government, legitimacy denotes a government system wherein government denotes the "sphere of influence." An authority viewed as legitimate often has the right and justification for exercising power. Political legitimacy is considered a primary condition for governing, without which a government will suffer legislative deadlock(s) and collapse. In political systems where this is not the case, unpopular regimes survive because they are considered legitimate by a small, influential elite [Dahl, p.124].
The principle indicates the acceptance of the decisions of government leaders and officials by (most of) the public because these leaders' acquisition and exercise of power have followed society's generally accepted procedures and political or moral values. Legitimacy may be conferred upon power holders in various ways in different societies, usually involving solemn, formal rituals of a religious or quasi-religious nature -- royal birth and coronation in monarchies, popular election and "swearing in" in democracies, and so on. "Legitimate" rulers typically require less use of physical coercion to enforce their decisions than rulers lacking in legitimacy because most people are apt to feel a moral obligation to obey the former but not the latter. Consequently, people who gain or hold power by illegitimate means tend to work very hard to discover or create ways of endowing themselves with legitimacy after the fact, often by inventing a new ideology or religion and attempting to indoctrinate the people with its legitimating formulas through various forms of propaganda, thus creating moral incentives for the citizenry to obey their government.
Dahl, Robert A. (1971). Polyarchy: Participation and Opposition. New Haven, London: Yale University Press. Legitimacy. A Glossary of Political Economy Terms. Retrieved from: http://webhome.auburn.edu/~johnspm/gloss/legitimacy.phtml