## Definition **Cartesian Doubt** is the systematic method of epistemic scepticism introduced by René Descartes in the *Meditations on First Philosophy* (1641): to find any certain foundation for knowledge, Descartes resolved to reject as false every belief he could not be absolutely certain of — treating as uncertain anything that could possibly be doubted. The method yields a single indubitable certainty: **"Cogito ergo sum"** ("I think, therefore I am") — the very act of doubting proves that a thinking thing exists. ## The Method of Doubt Descartes observed that the senses sometimes deceive (illusions, dreams) and that he could not rule out a powerful deceiving demon manipulating all his perceptions. He therefore suspended judgment on all beliefs that depended on the senses or on external reality. What survives this radical sceptical assault? The one thing he cannot doubt is the existence of his own act of doubting. Even if a demon is deceiving him about everything else, there must be a "him" being deceived. Hence the *cogito*: $\text{cogito ergo sum}$ This is not a syllogism but an immediate, self-validating insight: the thinking itself guarantees the existence of the thinker. ## Rationalist Foundations From the *cogito*, Descartes attempted to rebuild knowledge on purely rational grounds, without reliance on the senses. He argued that clear and distinct ideas — grasped by the intellect alone — are reliably true, that God exists and is not a deceiver, and that the external world therefore broadly corresponds to what reason tells us. This project places Descartes at the origin of Continental Rationalism: the view that reason, not experience, is the primary source of knowledge. ## Mind-Body Dualism The *cogito* establishes the mind as a thing whose entire essence is thinking (*res cogitans*), entirely distinct from the body, which is a material, extended thing (*res extensa*). This substance dualism raises what remains an open question in philosophy of mind: how does an immaterial mind causally interact with a material body? Warburton's book treats Descartes' move as foundational to the rationalist tradition and to modern debates about consciousness and personal identity. ## Historical Significance Descartes' method broke decisively with scholastic reliance on Aristotelian authority. By making the individual reasoning mind the ultimate arbiter of certainty, the *Meditations* inaugurated the modern philosophical project — the subject-centred epistemology that runs through Locke, Hume, and Kant. ## Related - [[Empiricism vs Rationalism]] - [[Plato's Theory of Forms]] - [[The Categorical Imperative]] ## Sources - [[A Little History of Philosophy (Warburton 2011)]]