Philosophy is the discipline concerned with questions of how one should live (ethics); what sorts of things exist and what are their essential natures (metaphysics); what counts as genuine knowledge (epistemology); and what are the correct principles of reasoning (logic). Modern philosophy is usually considered to begin after the philosophy of Immanuel Kant at the beginning of the 19th-century. German idealists, such as Hegel, expanded on the work of Kant by maintaining that the world is entirely rational and its nature is fundamentally knowable. Rejecting idealism, other philosophers, many working from outside the university, initiated lines of thought that would occupy academic philosophy in the early and mid-20th century. [Picture: Rodin's Thinking Man against a modern backdrop...more >>]