He Doubted Everything.
He Found One Thing He Could Not Doubt.

You spend a single night alone in a heated room near Ulm — a young French soldier with time to think — and emerge with three dreams you believe are divine instruction to unify all human knowledge through a single method. You spend the next decade working out what that instruction required. The three dreams: Descartes recorded the dreams in a journal that was lost but summarized by his early biographer Adrien Baillet in "Vie de Monsieur Descartes" (1691). The account is detailed enough to be considered reliable. The philosopher Geneviève Rodis-Lewis has analyzed the dreams as consistent with the psychological state of someone on the edge of a major intellectual synthesis: the anxiety of the first dream (the whirlwind), the external validation of the second (thunder, taken as divine confirmation), and the third (the books — a dictionary, representing knowledge, and an anthology of poetry, representing inspiration) as representing the synthesis of reason and imagination. Whether the interpretation is correct, the functional effect is well-documented: Descartes emerged from the winter room with a clear sense of mission and began working on what became the Discourse on Method.

In November 1633, you hear that Galileo has been condemned for defending the Earth's movement around the Sun — the same position your manuscript "Le Monde" argues. You are in the Netherlands, unpublished, unthreatened. You suppress the manuscript anyway. It is published fourteen years after your death. The suppression of Le Monde: Descartes' letters from November-December 1633 describe his reaction to the Galileo condemnation. He writes to Mersenne: "I have been so astonished by this that I have almost resolved to burn all my papers." He did not burn them; he suppressed them. "Le Monde" was finally published in 1664, fourteen years after his death. The physical cosmology it contains is largely superseded (he rejected the void and developed his own vortex theory of planetary motion, which Newton later displaced), while the mathematical and physiological work he published during his lifetime (the Discourse on Method and its appendices — including the Geometry, which invented coordinate geometry) proved more durable. The strategic calculation was not wrong.

You publish your method of reasoning as an essay with three scientific appendices. One appendix, almost as an aside, introduces a system for representing any geometric curve as an equation and any equation as a curve. Every student who has ever graphed a line or plotted a point on an x-y axis is using what you set down here, though you did not announce it as particularly important. The Geometry and coordinate systems: The mathematical historian Carl Boyer, in "A History of Mathematics," describes the publication of Descartes' Geometry as one of the pivotal moments in the history of mathematics: "In the history of mathematics there is perhaps no other work which has had such far-reaching influence as Descartes' Géométrie." The coordinate system (x and y axes, arbitrary naming of coordinates) appears almost casually in the course of solving specific geometric problems — Descartes didn't announce it as a major innovation but used it as a tool. Later readers — particularly Leibniz and Newton — recognized that the tool was more significant than the specific problems it was used to solve, and built calculus on it.

You publish a thought experiment asking whether an all-powerful demon might be deceiving you about everything you perceive — the external world, other minds, your own memory and reasoning. You mean it as a genuine philosophical challenge, not a curiosity. Philosophy has spent four centuries trying to answer it satisfactorily. The evil demon and modern philosophy: The philosopher Bernard Williams, in "Descartes: The Project of Pure Enquiry" (1978), argues that the evil demon thought experiment is the founding move of modern epistemology: it poses the question of how the mind can know anything about a reality external to it in its sharpest possible form. Descartes' own resolution (God as guarantor) was rejected by Hume (there is no certain knowledge of God either) and by Kant (but we can establish the conditions of possible experience without appealing to God). Contemporary philosophy of mind and epistemology (the "brain-in-a-vat" thought experiment in Hilary Putnam; the simulation hypothesis in Nick Bostrom) are all updated versions of the evil demon. The question is still genuinely open. Descartes posed it in the sharpest possible form, which is the most important thing a philosopher can do with an unsolved problem.

A princess in exile writes to ask you how your non-physical mind moves your physical hand — since you have defined mind and body as entirely different substances with no common properties. You are the most rigorous philosopher in Europe. You never adequately answer her. Neither has anyone since. Elisabeth and the mind-body problem: The Descartes-Elisabeth correspondence has been published in full and is considered philosophically significant independent of the Meditations. Elisabeth's first letter (May 16, 1643) poses the question with unusual precision: if the soul is merely a thinking substance, without extension or materiality, by what property can it move the body's material mechanisms? Descartes' responses acknowledge the difficulty and propose the pineal gland as the locus of mind-body interaction — an answer generally considered unsatisfactory even in the 17th century. Contemporary philosophy of mind (consciousness studies, philosophy of neuroscience) describes the "hard problem of consciousness" (David Chalmers, 1995) as the same problem: how does subjective experience arise from physical processes? Elisabeth asked it in 1643; we still don't have a satisfying answer.

You have slept until noon every day for twenty years, considering it essential to your best thinking. Queen Christina of Sweden summons you to Stockholm for philosophy lessons at 5 AM in a cold library in winter. You accept the invitation. You are dead four months later. The working conditions you spent two decades protecting turned out to be load-bearing. The Stockholm death: Descartes' correspondence from Stockholm, November 1649 through January 1650, shows increasing discomfort with the cold, the early hours, and the pace of court life. He wrote to Chanut (the French ambassador who had facilitated the invitation) that he was not thriving but felt obligated to the Queen. He developed pneumonia in late January after apparently treating a sick French diplomat, and declined rapidly. The doctor whom Queen Christina sent prescribed a treatment (bleeding) that Descartes refused, preferring to try tobacco and wine (his preferred remedies). He died February 11, 1650. He was fifty-three. His manuscripts were later collected and taken to France; his body was originally buried in Stockholm and moved to Paris in 1667, where it now rests in the church of Saint-Germain-des-Prés.

Your skull was separated from your body during the transfer of your remains from Stockholm to Paris. Multiple skulls were subsequently offered for sale as yours; one is now in the Musée de l'Homme. Your complete works were placed on the Index of Forbidden Books in 1663, thirteen years after your death. The mind-body problem you identified in 1643 is still philosophically unsolved. Descartes' intellectual legacy: The philosopher Richard Rorty, in "Philosophy and the Mirror of Nature" (1979), argues that the entire tradition of Western epistemology since Descartes has been organized around what he calls the "Cartesian anxiety" — the worry that if we can't establish certain foundations for knowledge, we can't know anything. This anxiety, posed by the evil demon and partially resolved by the cogito, is the generating problem of modern philosophy. Locke, Berkeley, Hume, Kant, Husserl, and Wittgenstein are all responses to Descartes' problem. The philosopher who creates the problem that others respond to for four centuries has done something philosophically significant regardless of whether their own proposed solutions are correct.

You sleep until noon every day of your adult productive life, calling the morning hours spent lying in bed your most intellectually active time. When you violate this condition — rising at 5 AM in a cold Stockholm library — you are dead within four months. The conditions that sustained your best work required protection, and you did not protect them from a queen. Descartes' working conditions: The historian Steven Nadler, in "A Book Forged in Hell" and other works, has analyzed the working conditions of 17th-century Dutch philosophers and notes that Descartes' long morning hours in bed were not idiosyncratic — many educated Europeans of his era remained in bed late, reading and corresponding, before rising for the day. What was unusual was his systematic protection of this time from interruption and professional obligation. The contrast with Leibniz (who worked in courts and bureaucracies, wrote mostly in travel coaches and waiting rooms) or Newton (who worked with frenzied intensity in concentrated bursts) suggests that the specific conditions were individual. What Descartes, Leibniz, and Newton share is the protection of thinking time from social demands — by different means but for the same purpose.