Meditations on First Philosophy — who's who

Born 1596 in La Haye en Touraine (now Descartes, Indre-et-Loire). Educated by the Jesuits at La Flèche — a thorough scholastic training he would spend his life trying to escape. Settled in the Netherlands in 1628 to write in peace. The Discourse on the Method appears in 1637; the Meditations in 1641; the Principles of Philosophy in 1644. Invited to Stockholm by Queen Christina of Sweden in 1649; required to give philosophy lessons at five in the morning in the Swedish winter; catches pneumonia and dies in February 1650 at fifty-three. The Meditations is the work he himself wished to be judged by.

The voice of the Meditations — the I who sits in the room, undertakes the doubt, finds the cogito, and builds outward to God and the world. Descartes writes carefully in the first person and present tense so that the reader is invited to perform the meditation rather than read a treatise about it. The meditator is, formally, Descartes himself; functionally, whoever the reader is willing to become for the duration. The literary device is part of the philosophical method: the certainty of the cogito is supposed to be felt, not merely understood, and felt only by someone who has actually gone through the doubt that produced it.

Introduced at the end of the First Meditation. Suppose there exists not a benevolent God but a powerful and malicious spirit — a malin génie, sometimes translated evil genius or evil demon — who has devoted all his power to deceiving me. Suppose he has so constructed my mind that everything I perceive, including the simplest arithmetic, is part of the deception. The hypothesis is the strongest form of doubt Descartes can conceive, and the one he must defeat to recover any knowledge at all. The cogito defeats it: even if the deceiver makes me wrong about everything else, he cannot make me wrong that I, the deceived, exist. The evil deceiver is the direct ancestor of every later philosophical scenario — brains in vats, computer simulations — in which the reliability of the external world is put in question.

Theologian and philosopher of the Port-Royal Jansenist circle. His objections are the sharpest in the set that accompanied the published Meditations, and they contain the formal statement of what came to be called the Cartesian Circle: Descartes seems to need clear and distinct perception to establish God's existence, and God's existence to validate clear and distinct perception. Descartes's reply is patient and precise, distinguishing the certainty of clear and distinct perception in the moment from the validation of memory across time. The Fourth Objections and Replies are, by themselves, one of the great short philosophical exchanges of the seventeenth century.

Not a character in the Meditations itself but the most acute philosophical correspondent of Descartes's later years. Elisabeth — exiled Bohemian princess living in The Hague — read the Meditations and wrote to Descartes in 1643 with the question that would haunt the system: if mind and body are really distinct substances, how can the mind move the body and the body affect the mind? Descartes's letters to her are the most personal of his philosophical writings, and they show him trying, and not entirely succeeding, to answer her. She made the interaction problem famous and pushed Descartes to confront the limits of his own dualism.

The dean and doctors of the sacred faculty of theology in Paris, to whom Descartes formally dedicates the Meditations. The dedication is a deferential letter explaining that the book provides philosophical demonstrations of God's existence and the soul's distinctness from the body — two propositions the Lateran Council of 1513 had urged Christian philosophers to prove by natural reason. The political purpose is unmistakable: Descartes had watched what happened to Galileo in 1633. The dedication did not secure their endorsement; the Meditations was placed on the Index of Forbidden Books in 1663, thirteen years after Descartes's death.