Descartes' evil demon and the Meditations

In 1641 the French philosopher René Descartes published Meditations on First Philosophy in Latin in Paris, with a set of objections by other thinkers and his replies. The book is written as six meditations over six days. In the first, he resolves to doubt everything that can be doubted, in order to find a foundation that cannot be shaken. The senses sometimes deceive, so he cannot trust them. Dreams show that waking life might be a dream. He then supposes that a supremely powerful and cunning evil demon is working to deceive him about everything, even simple arithmetic and the existence of the physical world.¹²

In the second meditation he finds one thing the demon cannot touch: even if he is being deceived, there must be an I that is deceived. The statement I am, I exist is certain each time he thinks it. This is the cogito. The phrase cogito ergo sum, I think, therefore I am, is not in the Meditations. It appears in French in the Discourse on Method of 1637 and in Latin in the Principles of Philosophy of 1644. Descartes then argues for the existence of God, claims that a good God would not let him be systematically deceived, and concludes that his clear and distinct perceptions are reliable. Critics, starting with Antoine Arnauld, said the argument runs in a circle. Others pointed out that Augustine had earlier argued that if I am mistaken, I exist.¹²

The Meditations set the agenda of modern philosophy: how can I know anything beyond my own mind, and how are mind and body related? Descartes defended mind-body dualism, which later thinkers found hard to explain. The demon has descendants in Putnam's brain in a vat and in films such as The Matrix.¹