Rousseau was well versed in music, and wrote ballets and operas; he could easily have been successful as a composer, but the stage made his Swiss Calvinist sensibilities uneasy. One day he was walking to visit his friend and fellow philosopher Denis Diderot, who was in jail, and he had an epiphany: modern progress had corrupted rather than improved mankind. He became famous overnight upon publication of his essay A Discourse on the Sciences and the Arts (1750). The essay informed nearly everything else he wrote, and eventually he would turn away completely from music and the theater to focus on literature.
In Discourse on the Origin of Inequality (1755) he continued to explore the theme that civilization had led to most of what was wrong with people: living in a society led to envy and covetousness; owning property led to social inequality; possessions led to poverty. Society exists to provide peace and protect those who owned property, and therefore government is unfairly weighted in favor of the rich. In it, he wrote: “The first man who, having enclosed a piece of ground, bethought himself of saying This is mine, and found people simple enough to believe him, was the real founder of civil society. From how many crimes, wars, and murders, from how many horrors and misfortunes might not any one have saved mankind, by pulling up the stakes, or filling up the ditch, and crying to his fellows: Beware of listening to this imposter; you are undone if you once forget that the fruits of the earth belong to us all, and the earth itself to nobody.” His next two books, a criticism of the educational system (Émile) and a treatise of political philosophy (The Social Contract), both published in 1762, caused such an uproar that he fled France altogether. His work would prove inspirational to the leaders of the French Revolution, and they adopted the slogan from The Social Contract: Liberty, Equality, Fraternity.
He grew increasingly paranoid in his later years, convinced that his friends were plotting against him. He spent some time in England with David Hume, but his persecution complex eventually alienated him from most of his associates, and he found comfort only with Thérèse, whom he finally married in 1768.