René Descartes
1596–1650, France, the Dutch Republic and Sweden
Rationalism
Doubt everything you can, and see what survives.
“I think, therefore I am.”
The life
Descartes was born in a small town in Touraine now named after him, and educated at the Jesuit college of La Flèche, which gave him a thorough scholastic training he later spent his career dismantling.
After studying law he enlisted as a gentleman soldier during the Thirty Years' War. On 10 November 1619, quartered in a stove-heated room near Ulm, he had three vivid dreams he took as a sign that he should reconstruct knowledge on mathematical foundations.
He moved to the Dutch Republic and stayed about twenty years, working in relative isolation and moving house constantly. When Galileo was condemned in 1633 he suppressed his own physics treatise rather than risk the same. His daughter Francine died at five, which he called the greatest sorrow of his life. In 1649 he went to Stockholm to tutor Queen Christina, who wanted lessons at five in the morning. He died there within months, probably of pneumonia.
What shaped the ideas
The certainty of the medieval picture had collapsed. Copernicus had moved the earth, Montaigne had revived ancient scepticism, and religious war had made competing authorities lethal. The question was whether anything could be known at all.
Descartes' response was to stop appealing to authority entirely and rebuild from a single indubitable point, using a method modelled on geometry. He was also a working mathematician and physicist: Cartesian coordinates are his, and the philosophy was meant to ground the science.
Core arguments
- 01
Methodic doubt
To find certainty, provisionally reject anything that admits any doubt at all.
A single rotten foundation stone compromises the building. Rather than examine beliefs one at a time, attack their sources: the senses sometimes deceive, dreams are indistinguishable from waking while they last, and even mathematics could be manipulated. Whatever survives all of that is genuinely secure.
- 02
The evil demon
Suppose a powerful deceiver is faking every experience you have.
This is a device to push doubt to its limit, covering even beliefs that survive dreaming, such as arithmetic. It is the ancestor of the brain in a vat and the simulation argument, and its role is methodological rather than a claim that any such demon exists.
- 03
The cogito
Even total deception proves a deceived thinker exists.
To be deceived, you must be something. The demon can falsify the content of every thought but cannot make it the case that nothing is thinking while thinking is occurring. The certainty is available only in the first person and only while you are actually thinking it.
- 04
The real distinction
Mind and body are two different kinds of substance.
I can clearly conceive of myself existing as a thinking thing while doubting that any body exists, so thought does not depend on extension. Body is extended and divisible; mind is unextended and indivisible. Two things with contradictory essential properties cannot be one thing.
Commonly got wrong
- The cogito is not a syllogism with a suppressed premise. Descartes insists it is grasped in a single act of intuition, not inferred from "everything that thinks exists".
- He is not a sceptic. Doubt is a method he uses deliberately and then exits; by Meditation VI he has argued his way back to an external world.
- Dualism's fatal problem was raised in his lifetime by Princess Elisabeth of Bohemia: how can an unextended mind move an extended body? His answer, involving the pineal gland, satisfied nobody, including him.
Works
Discourse on the Method 1637
Published in French, not Latin, so ordinary readers could follow. Contains the cogito in its famous form.
Meditations on First Philosophy 1641
Six meditations, published with objections from Hobbes, Gassendi and Arnauld, plus his replies.
Principles of Philosophy 1644
The complete system, intended as a university textbook to replace the Aristotelian ones.
Passions of the Soul 1649
His late work on emotion, written partly in response to Princess Elisabeth's questions.
Meditations I and II. Roughly fifteen pages, and they contain the doubt, the demon and the cogito.
Why they still get taught
He made the first-person point of view the starting place for philosophy, which is why the mind-body problem is still framed his way. Modern epistemology is largely a long argument with Meditation I.
Chapters
- I Think, Therefore I Am · The Modern Turn
- The Mind-Body Problem · The Hard Problem