An Essay Concerning Human Understanding: all four books in a single file

According to Wikipedia: "John Locke (29 August 1632 – 28 October 1704), widely known as the Father of Liberalism, was an English philosopher and physician regarded as one of the most influential of Enlightenment thinkers. Considered the first of the British empiricists, he is equally important to social contract theory. His work had a great impact upon the development of epistemology and political philosophy. His writings influenced Voltaire and Rousseau, many Scottish Enlightenment thinkers, as well as the American revolutionaries. His contributions to classical republicanism and liberal theory are reflected in the American Declaration of Independence."