Philosophers, including Jean-Jacques Rousseau, Voltaire, and Denis Diderot, developed new social ideas during the Enlightenment period that were based on reason and methods of scientific inquiry. Jean-Jacques Rousseau in this time played a significant role in social theory. He revealed the origin of inequality, analyzed the social contract (and social compact) that forms social integration and defined the social sphere or civil society. Jean-Jacques Rousseau also emphasized that man has the liberty to change his world, an assertion that made it possible to program and change society.