Legitimacy is both a normative and empirical concept in political science.
Normatively, to ask whether a political system is legitimate or not is to ask whether the state, or government, is entitled to be obeyed. As such the idea of legitimacy is connected with the legal concepts of de jure and de facto power. Whatever the accepted grounds of political obligation may be, legitimacy refers to these. Its more interesting application, however, may be in the empirical usage, especially in political sociology. Here the concentration is principally on how any given political system comes to be seen as 'legitimate' by a majority of its citizens.