The establishment of public education systems was the result of the Enlightenment, an intellectual movement in the 17th and I 8th centuries which espoused the power of human reason to improve society, and which promoted the use of science to understand the natural world and the place of humans in the world. Immanuel Kant defined the Enlightenment as the human transition from an era of ignorance to an era of reason with a consequent expansion in human freedom. Jean-Jacques Rousseau, one of the key philosophers of the Enlightenment, proposed the twin ideas that the legitimacy of a social contract depended on the extent to which it was accepted by those it governed, and the idea that education prepared people to accept the social contract or to build a new contract.