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René Descartes (1596–1650) is widely regarded as the father of modern philosophy. A French mathematician, scientist, and philosopher, Descartes broke decisively with the medieval Aristotelian-Thomistic tradition and sought to rebuild human knowledge from the ground up on a foundation of absolute certainty. His philosophical method of radical doubt, his discovery of the cogito, his substance dualism, and his arguments for God’s existence are all central to AQA A-Level Religious Studies. His principal philosophical works are the Meditations on First Philosophy (Meditationes de Prima Philosophia, 1641), the Discourse on Method (1637), and the Principles of Philosophy (1644).
In the Meditations, Descartes set out to find a proposition that is absolutely certain — immune to any possible doubt. To do this, he employed a method of systematic, hyperbolic doubt: he resolved to reject as false anything that could conceivably be doubted, no matter how unlikely the grounds for doubt. His aim was not to become a sceptic but to find an indubitable foundation on which to build the edifice of knowledge.
Descartes identified three progressively more radical grounds for doubt:
The evil demon hypothesis represents the most extreme form of scepticism. If even mathematics and logic can be doubted, what — if anything — survives?
In the Second Meditation, Descartes discovered the one proposition that survives even the most radical doubt:
“But there is a deceiver of supreme power and cunning who deliberately and constantly deceives me. In that case, I too undoubtedly exist, if he deceives me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So, after considering everything very thoroughly, I must finally conclude that the proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind.” — Descartes, Meditations, II
This is the famous cogito (from the Latin cogito, ergo sum — “I think, therefore I am”, a formulation that appears in the Discourse on Method). The argument is deceptively simple but profoundly powerful:
Descartes concluded that the cogito provides an Archimedean point — a fixed, immovable foundation on which all other knowledge can be rebuilt. He also concluded that he is, in his essential nature, a thinking thing (res cogitans) — a mind or consciousness whose existence is more certain than anything in the physical world.
From the cogito, Descartes developed his theory of substance dualism — the view that reality consists of two fundamentally different types of substance:
Descartes argued that mind and body are really distinct — each can exist without the other:
Despite their distinctness, Descartes acknowledged that mind and body are intimately united in human beings. In the Sixth Meditation, he wrote that the mind is not lodged in the body “as a sailor in a ship” but is “very closely joined and, as it were, intermingled with it.” He suggested that the pineal gland in the brain is the point of interaction between mind and body, though this proposal was widely criticised even in his own time.
Descartes’s dualism faces a formidable philosophical objection known as the interaction problem, raised most forcefully by Princess Elisabeth of Bohemia in her correspondence with Descartes (1643):
“How can the soul of a man determine the spirits of his body so as to produce voluntary actions, given that the soul is only a thinking substance?” — Princess Elisabeth to Descartes, 6 May 1643
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