Abstract
In Le Contrat Social, attempting to "consider if, in political society, there can be any legitimate and sure principle of government" , Jean-Jacques Rousseau (1712-1778) took up the problem of legitimacy which has remained a burning issue throughout history, especially when people talk about "the global crisis of legitimacy of liberal democracy". However, before trying to determinate how power may be rendered legitimate, the concept of legitimacy itself should be carefully defined. As Jean-Marc Coicaud said, "the idea of legitimacy concerns first and foremost the right to govern". In Latin, legitimus meant "lawful, according to the law", this "right to govern" should not be assimilated to legal validity. A power should be established in conformity to the law to be legitimate but a power lawfully established is not necessary legitimate since "belief in legality presupposes the legitimacy of the legal order that lays down the law".
