On this night in 1619, after a night in which he swears he was not carousing, René Descartes went to bed in an overheated, stuffy room in Ulm, and had three vivid dreams to which he later attributed the eventual course of his life.

In the first dream, a strong wind battered Descartes, and he sought shelter in the church of a college, only to be pushed back by the winds. After the winds abated he found himself surrounded by upright people, while he himself tottered along, leaning to the left. In the second dream, he perceived a loud thunderclap and saw the room filled with sparks of light. This apparently was a recurring dream for Descartes, so he meditated on logic until he fell asleep. (It’s like counting sheep, but for intellectuals.)

In the third dream, Descartes felt no terror, but instead came upon a book of verse, the first line of which read “Quod vitae sectabor iter?” and another poem, presented to him by an unknown man, with the first line “Est et non.” Which way of life shall I choose? It is and it is not.

It’s no tolle lege, but it’s surely proof that the universe has a sense of humor, having a man who would be identified with rationalism and whose books and teachings would be periodically banned, get his inspiration from a dream about a church. Descartes grew into a philosopher (and mathematician) whose method, more than his beliefs, distinguished him from the Scholastics, a method of metaphysical doubt: proceeding by extreme skepticism, he would discern those true principles which struck him as clear and distinct. And from there, he hoped, one could construct science upon firm foundations:

Archimedes, that he might transport the entire globe from the place it occupied to another, demanded only a point that was firm and immovable; so, also, I shall be entitled to entertain the highest expectations, if I am fortunate enough to discover only one thing that is certain and indubitable. (Meditations II.)

Descartes presents this new method of doubt in the aptly titled Discourse on the Method (1637), but nowhere so vividly as in the Meditations on First Philosophy (1641), in which he presents himself as a restless thinker, sitting by the fire in his pajamas (lit. toga),who over the course of six days meditates on what he can know with certainty, doubting his experiences (for has he not had similar experiences in dreams?) His first intermediate conclusion, a barbaric yawp: I am, I exist, I am a thinking thing. The famous formulation cogito ergo sum is not in the Meditations; some philosophers argue that this is omitted because Descartes did not think of the conclusion as an inference, but as a truth of unshakeable immediacy.

Descartes circulated the manuscript of the Meditations to the leading theological and philosophical thinkers of his day, and in an act that earned him the love of historians of philosophy, published the objections and replies as an addendum to the first edition. The critics press Descartes on a number of points, but they can be summarized by noting that while Archimedes needed a solid place to stand in order to move the world, he also needed a lever. Arguing from I am a thinking thing to the reality of God, logic, and the external world did not prove to be an easy task, and whether Descartes’ argument succeeds or falls to circularity is still the subject of scholarly debate.

I once was fortunate enough to hold in my hand an early (first or second edition) copy of the Meditations. It was fat, and fit easily in the palm of my hand, about the size of a book of prayers. It would have fit snugly in the pocket of a jacket. While it would be irresponsible to conclude anything about Descartes’ intentions or hopes from the small size of the book (many factors determine the size of a book), speculating is irresistible: the book of dreams from a dreamer, a book of meditations for the modern scientist from a man whose aspirations were much more modest:

Of philosophy I will say nothing, except that when I saw that it had been cultivated for so many ages by the most distinguished men; and that yet there is not a single matter within its sphere which is still not in dispute and nothing, therefore, which is above doubt, I did not presume to anticipate that my success would be greater in it than that of others.