After more than a millennium of medieval scholasticism, philosophy was reborn in the seventeenth century with René Descartes (1596–1650), often called the Father of Modern Philosophy. In his Meditations on First Philosophy, Descartes introduced Cartesian doubt, a method of systematic skepticism in which he set aside every belief that could possibly be doubted — including the possibility raised by his Evil Demon hypothesis that a powerful deceiver might be causing all sensory experience to be false. From this wholesale doubt emerged the one indubitable certainty: "Cogito, ergo sum," I think, therefore I am. The very act of doubting, Descartes argued, proves the existence of the thinking self. Building on this foundation, he proposed Cartesian dualism, the view that mind and body are two fundamentally different substances — the non-physical res cogitans and the physical res extensa.
Across the English Channel, John Locke (1632–1704), the Father of Liberalism and a founder of British empiricism, approached the same modern questions from a different direction. His Essay Concerning Human Understanding argues for tabula rasa, the blank slate: the mind at birth has no innate ideas, and all knowledge comes from experience, both sensation and reflection. Locke even grounded personal identity in continuity of consciousness, defined through memory rather than the soul or body. Politically, his social contract theory argued that governments derive their authority from the consent of the governed and exist to protect natural rights to life, liberty, and property — rights that precede any political arrangement.
David Hume (1711–1776) pushed British empiricism to its skeptical limits. In his Treatise of Human Nature, Hume insisted that all knowledge derives from sense experience and applied that principle with devastating rigor. His problem of induction asks how we can rationally justify believing the future will resemble the past — inductive reasoning, he concluded, rests on habit, not logic. Hume's Fork distinguishes relations of ideas (analytic truths like mathematics, certain but uninformative about the world) from matters of fact (synthetic claims about empirical reality, probable but never certain). Examining causation, Hume denied that we ever observe any necessary connection between events; what we call cause is merely constant conjunction, one event regularly following another. His Bundle Theory of the Self carries the same logic inward: there is no enduring self, only a bundle of perceptions — impressions and ideas — in constant flux.