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Last Updated on May 5, 2015, by eNotes Editorial. Word Count: 1758

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.

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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 to the more difficult task of proving the existence of the material world. For this purpose, he introduces the famous “wax argument”: A piece of wax fresh from the beehive can be seen to have color, size, and smell that present themselves to human senses, but if the wax is placed near a fire it melts and those qualities disappear. Where did they go? Descartes’s answer is that there had only been the assumption that the qualities existed in the object, while in fact they were merely intuitions of the mind. The best that humans can do at this point is to speculate that there are material objects outside themselves that cause sensations in the mind.

Descartes’s third meditation is devoted to a proof of God’s existence, which is also intended to show that the world perceived through the senses is not a deception. Since the existence of the outside world is still in doubt, Descartes begins by examining the ideas present in his mind. He notices that some ideas seem to be “born” with him, while others seem to come from outside; he observes that things seem to be happening around him and independently of his will. For example, as he sits by the fire he feels heat and is persuaded that the heat does not originate from within him; similarly, he has a concept of God, which also does not seem to have come from within him. He asks himself how, given that he himself is not an infinite, all-knowing, all-powerful being, he could produce the idea of a God with these attributes. Because he does not possess these qualities, Descartes argues, they could not have originated within him, and since God is perfect, he could not be a deceiver. Therefore, the world he perceives through his senses must have been created by a being greater than himself, and if God is not a deceiver, the world he perceives must be the “real” world and not an illusion. Thus, in establishing the existence of God, Descartes established the foundation of all knowledge.

In the fourth meditation, Descartes points out that even though ideas such as the self and God are perceived clearly and distinctly, humans make errors in their thinking because their intellects are finite and they possess free will. This is not an imperfection on God’s part but merely a sign of the imperfection of human beings. Since he is not himself the Supreme Being, he says, he should not be surprised that he occasionally falls into error. The power of free will received from God is perfect, but sometimes the will surpasses the understanding, which causes error.

In the fifth meditation, Descartes discusses the essence of material things. To determine further whether anything certain can be known about material things, he presents a second argument for God’s existence, which states that just as within the idea of a triangle is contained the concept of “three angles,” the idea of “existence” is necessarily contained within the concept of “God.” To speak of a “nonexistent God,” he says, would be a contradiction, because the property of existence is a part of God’s essence. The logical certainty of God’s existence means that all things depend upon God for their existence and that God, being perfect, could not be deceiving humans about the external world. Thus, Descartes feels assured that the certainty of the existence of the material world is guaranteed by the certainty of God’s existence.

In the sixth and final meditation, Descartes completes his argument as to whether material things exist. He begins by differentiating between “extended things” out in the world, and “thinking things” in his mind. Descartes believes that it is certain that material things exist, and the fact that they can be described with the clear and distinct ideas of mathematics supports the certainty that there is an objective reality independent of the human mind. In addition, because God is not a deceiver, Descartes has no reason to believe that what he himself perceives as the material world is not really there.

What Descartes has established with this line of thinking is that there are actually two realities: mind and matter. In terms of Descartes’s own existence, his mind is distinct from his body; but if the human body is a material machine, how can the immaterial mind act upon it? Descartes simply answers that it does, like a captain who lives inside his ship. Perhaps, he suggests, God arranges the interaction of mind and body in mysterious ways, beyond finite understanding.

Descartes was one of the most original thinkers of his time. By using mathematics as his model of certain knowledge, he believed that he had placed all of human knowledge on a firm foundation. Philosophy, he believed, like mathematics, must start with clear and simple truths and then advance toward more complex truths. By showing with absolute certainty that he exists—“I think, therefore I am”—and that God exists, he proceeded to show that the external world exists as well, even though humans may err in their perceptions about the world.

The English philosopher John Locke challenged Descartes’s notion of innate ideas, believing instead that at birth human beings’ minds are a tabula rasa, or “blank slate”—devoid of any ideas of self or God. The German philosopher Immanuel Kant disputed Descartes’s proofs for God’s existence, especially the proof contained in the fifth meditation. It certainly does not follow, Kant claimed, that something can be asserted to exist merely because it can be conceived.

Descartes acknowledged his critics through his friend and fellow mathematician Marin Mersenne, who sent copies of Descartes’s manuscript to contemporary philosophers and theologians. When their criticisms were returned to him, Descartes in turn commented on them and published the entire discussion along with Meditations on First Philosophy.

In breaking with Scholasticism, a mode of philosophical thinking that had lasted for almost four hundred years, Descartes was a major influence on every philosopher who came after him. By making a clean sweep of the philosophical landscape and attempting to build it from the foundation up, Cartesian philosophy raised many new difficulties and provoked a host of questions that have continued to challenge philosophers.

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