The appearance of Meditations on First Philosophy in 1641 marked a dramatic turning point in the history of Western thought. Born in France in 1596, René Descartes was sent to a Jesuit school as a young man and in 1616 obtained a law degree. He spent much of his youth traveling. Like many young Frenchmen of the time, he enlisted as a gentleman volunteer in the army of Prince Maurice of Nassau in Holland during the Thirty Years’ War. In November, 1619, when the onset of winter had slowed the fighting, Descartes retired to the village of Ulm on the Danube River to devote himself to study and contemplation. He wrote that one day, while trying to escape the cold in a heated room, he had three visions or dreams in which he saw flashes of light and heard thunder. He said it seemed to him that some spirit was revealing a new philosophy to him. He interpreted these visions as a divine sign that it was his destiny to place all of human thought on the firm foundation of mathematics.

In 1637, Descartes had published Discours de la méthode (Discourse on Method, 1649), which roughly outlined that new philosophy. Both Discourse on Method and Meditations on First Philosophy were written in French rather than Latin, the usual language of scholarly works. Like Galileo before him, who wrote in Italian, Descartes intended to reach beyond the university to a larger educated audience.

The great intellectual tension of Descartes’s time was that between belief in traditional Christianity and belief in the potential of the new physical and mathematical sciences. Philosophers before Descartes used a philosophical method called Scholasticism, which was entirely based on comparing and contrasting the views of recognized authorities, especially Aristotle. Since Scholastic philosophy was built on the opinions of many thinkers, it could not provide much in the way of certainty on any given subject.

Instead of accepting the traditional views, Descartes believed that people must instead study from “the great book of the world.” To know the opinions of others, he said, is history, not science; people should do their own thinking, and the clear and simple process of mathematics would provide the clue for how to proceed on the path to certain knowledge. Descartes turned all questions of human knowledge inward by first thinking about the process of thinking itself, examining the method of knowing as a prerequisite for assuming that certain knowledge has been attained. Descartes was trying to find a body of irrefutable and self-evident truths that every person of common sense and reason could accept. If truths could be established in philosophy as they had been in mathematics, this would end the debates about the existence of God, the immortality of the soul, and the reality of the external world.

In the first meditation, Descartes begins by doubting all knowledge that he has previously accepted as true. Up to the present time, he says, he has accepted the knowledge acquired through sensory experience as the truest and the most certain knowledge; yet sense perceptions may be illusions, the products of dreams or hallucinations, or the products of an all-powerful being causing these sensations or ideas to form. Individuals could be existing in a prolonged “dream state” that seems quite real while there is no way to prove that they are awake. These facts led Descartes to doubt the certainty of everything. The only thing he could not doubt was that he existed.

In the second meditation, Descartes declares that this universal doubt makes him feel like a swimmer who is suddenly plunged into deep water. Unable to touch bottom or see the surface, he cannot find a fixed reference point from which to begin. He therefore must assume that everything is false and that he has no memory, no senses, and no body. Even what he perceives as “reality” could possibly be a deception. Even if, however, he is in a state of universal doubt—even if he is being deceived—he remains a thinking being. He can therefore at least assert that he is “a thing which thinks.” At this point he has found the first of what he calls “clear and distinct ideas,” ideas so certain that they cannot possibly be denied.

Descartes can now proceed...

(The entire section is 1758 words.)