Rousseau argued in his "Discourse on the Origin of Inequality" (1755) that humans are naturally free and roughly equal, and that the deep inequalities of civil society arose historically through the invention of private property rather than from nature. In "The Social Contract" (1762) he argued that legitimate political authority can only derive from the "general will" of the people, so that individuals who submit to laws they have collectively authored remain free even under binding common rules.
Intellectual setting
Rousseau wrote as a contributor to and later sharp critic of the French Enlightenment's faith in progress through arts and sciences, and both "Emile" and "The Social Contract" were banned and publicly burned in Paris and Geneva shortly after publication, forcing him into exile.
Key ideas
The general will
Rousseau argued that legitimate political authority rests on a social contract in which each person submits to the collectively formed "general will" aimed at the common good, so that obedience to law made this way is compatible with, and even constitutes, genuine freedom.
Natural goodness corrupted by society
Rousseau argued that human beings in a hypothetical state of nature were free and largely equal, and that the deep inequalities and moral corruption of civilized life resulted from the historical emergence of private property and the social comparisons it generates, not from natural human depravity.
Legacy
Rousseau's theory of popular sovereignty profoundly shaped the political thought of the French Revolution, his account of moral autonomy influenced Kant's ethics, and "Emile" shaped modern theories of child-centered education.