A person, institution, or organization is said to have authority when the power it exercises is supposed legitimate, that is, authorized by some system of norms to which the speaker assents. The emergence of such norms in human society is a complex matter, with convention, habit, custom, and tradition playing different roles. Social contract theory is one kind of solution to the problem of the basis of authority; the evident utility of some rule-governed systems is another. While it is common to find scepticism about particular claims to authority, the idea that human co-ordination (and hence even communication) could exist without it is usually regarded as fanciful.