'Our Descartes, born to uncover the errors of antiquity, but to substitute his own, and spurred on by that systematizing mind which blinds the greatest of men, imagined that he had demonstrated that the soul was the same thing as thought, just as matter, for him, is the same thing as space. He affirmed that we think all the time, and that the soul comes into the body already endowed with all the metaphysical notions, knowing God, space, the infinite, having all the abstract ideas, full, in fact, of learning which unfortunately it forgets on leaving its mother's womb.'

Voltaire’s portrait of Descartes is instantly recognizable today; indeed his estimate of Descartes is one on which many of us have been brought up, especially in the English-speaking world. Descartes is the father of modern philosophy, but he was led astray by his passion for system; he tried to derive factual truths about the world from principles that are supposedly known a priori. In short, although, Voltaire does not use the term, his Descartes is very much a rationalist. Moreover, like many modern readers, Voltaire tends to associate Descartes primarily with a distinctive set of doctrines in the philosophy of mind.