Descartes’ Three Dreams happened on the night of November 10, 1619, the culmination of days of fevered concern with the search for truth. In the First Dream, Descartes is walking through the streets haunted by terrifying phantoms. A severe weakness in his right side forces him to bend over to his left. He tries to straighten up, but a whirlwind spins him three or four times on his left foot. More frightening is the thought that he is falling at every step he takes. Then he enters through the open gates of a college, seeking relief and intending to pray in the college chapel. But he has passed someone he knows without hailing him. He tries to turn back to greet him, but the wind hurls him against the chapel. At the same time he sees in the college courtyard another person who greets him and tells him that “Monsieur N.” has something to give him. Descartes imagines it is a melon brought from a foreign country. The people standing around him are firm on their feet, whereas he is staggering about, even though the wind has abated. Then he awakes with a pain making him fear that an evil demon is leading him astray. He rolls over from being on his left side (where he had fallen asleep) and prays to God for protection from the dream's evil effects and from the misfortunes that might invite divine retribution for his sins, though others might have thought that hitherto he has led an upright life.

Falling asleep after a couple of hours thinking about the good and evil in the world, Descartes has the Second Dream. A piercing noise, he thinks a thunderclap, frightens him back to the waking state, and on opening his eyes he sees about him large numbers of fiery sparks. This is not the first time he has woken up to find his eyes emitting sparks by which he could see objects close by. Finding a satisfactory natural explanation of the strange phenomenon, he falls asleep again.

A moment later there is the peaceful Third Dream. Descartes finds a book on his table without knowing who put it there. It is a “Dictionary” (Dictionnaire, as in Baillet), and he expects to find it useful.