John Locke was born in 1632 in England to a lawyer. He studied at Westminster School and Oxford University, where he was introduced to new philosophies and sciences. He worked as a physician for prominent politicians, including the Earl of Shaftesbury. After Shaftesbury was tried for treason, Locke fled to Holland for safety. It was there that he wrote his masterpiece "Essay Concerning Human Understanding," in which he argued that the limits of human knowledge are defined not by what exists in reality, but by what the human mind is capable of apprehending through our senses and reason.