The English philosopher and political theorist John Locke (1632-1704) laid much of the groundwork for the Enlightenment and made central contributions to the development of liberalism. Trained in medicine, he was a key advocate of the empirical approaches of the Scientific Revolution. In his “Essay Concerning Human Understanding,” he advanced a theory of the self as a blank page, with knowledge and identity arising only from accumulated experience. His political theory of government by the consent of the governed as a means to protect the three natural rights of “life, liberty and estate” deeply influenced the United States’ founding documents. His essays on religious tolerance provided an early model for the separation of church and state.