In Meditations on the First Philosophy, René Descartes delves into epistemology, or the theory of knowledge. He asks questions such as whether there is such a thing as knowledge, and if so, what distinguishes it from opinion. However, in order to answer these questions and to validate knowledge, it was necessary to raise the fundamental questions of being.

Descartes chooses to present his thoughts as meditations; he represents himself as seated before a fire in a cozy Dutch dwelling, wrapped in his dressing gown, freed from worldly care, and ready to devote himself to a task to which he had for some time looked forward, a kind of mental housecleaning. On six successive days, he pursues his meditation, step by step, clearing his mind of all error.

In Discours de la méthode (1637; Discourse on Method, 1649), Descartes reveals that the work was actually composed in very similar circumstances. In 1628, Descartes was in his thirties and living in Holland; he had withdrawn from a more active life for the special purpose of carrying on his philosophical and scientific investigations. Meditations on First Philosophy was circulated in manuscript, and when it was published in 1641, it included a lengthy appendix composed of objections by leading philosophers—including Thomas Hobbes and Pierre Gassendi—together with Descartes’s replies.

The First Meditation

The First Meditation is, in a way, distinct from the rest. It describes Descartes’s effort, which in fact engaged him for many years, to accustom himself not to think of the world in the imagery of the senses or according to the notions of common sense and the traditions of various schools of thought.

Can it be, Descartes wonders, that all beliefs that he had formerly held are false? Perhaps not, but if he is to achieve his goal of building up a body of incontrovertible truth, he must exercise the same rigor toward beliefs that are merely uncertain as toward those that are demonstrably untrue. That is to say, he must make doubt his tool. Instead of allowing it to hang over him, forever threatening, he must grasp it firmly and lay about until he has expunged from his mind every pretended certainty.

The first to go are those beliefs that depend on the senses—notably one’s belief in the existence of one’s own body and of everything that appears to the sight and touch. One’s habitual judgment protests. What can be more certain, Descartes asks himself, than that I am seated by the fire holding this paper in my hand? However, he writes, when one reflects that one’s dreams are sometimes attended with equal confidence, one is forced to conclude that there is no infallible mark by which one can know true perceptions from false.

Of course, what one doubts is, in this case, only that one’s ideas represent something beyond themselves. Descartes is one of the first philosophers to use the word “idea” in the modern sense. He means by it “whatever the mind directly perceives.” However, he distinguishes between the idea taken only as a mode of thought and the idea as a representation of...

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The Second Meditation

Descartes’s aim in the Second Meditation is to discover, if possible, some foundation of certainty that doubt is powerless to assault. He has doubted the reality of the world presented to him through his senses. Shall he affirm that some god (or devil) must exist to put these ideas into his mind? That hardly seems necessary, for perhaps he has produced them himself. One thing, however, seems now to loom up in Descartes’s mind: “I myself, am I not something?” Suppose all his ideas are hallucinations, whether self-induced or planted in him by some god or devil. In this, at least, he cannot be deceived: “I am, I exist, is necessarily true each time that I pronounce it, or that I mentally conceive it.”

Here, then, for the first time, Descartes presents a self-validating judgment. It is the unique instance in which people immediately encounter the existence that is represented to them by an idea: One has an idea of “oneself.” Like other ideas, this one claims to have objective reality. However, unlike other ideas, this one’s claim is open to inspection—by the self. Both the idea and the existence that it represents are present each time one thinks them. In a simple act of “mental vision” (to use Descartes’s expression), one knows that one exists. As the philosopher John Locke would say, one knows one’s own existence intuitively.

With this certitude to serve as a cornerstone, Descartes proceeds to raise his palace of Truth. If one explores the structure of one’s inner...

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The Third Meditation

Descartes’s argument takes two forms. First, he asks directly concerning the idea of a perfect being, whence it could have come into his mind: From some other creature? From himself? Or must there exist a perfect being to originate the idea? His answer is obscured for the modern reader by the late-medieval philosophical framework in which it is expressed. The idea of God contains more “objective reality” than any other idea (including one’s idea of self). However, a more perfect idea cannot be generated by a less perfect being. Therefore, the idea of God in his mind must have been placed there by God himself.

The second form of the argument proceeds from the contingent quality of his own existence, made up as it is of fleeting instants, not one of which is able either to conserve itself or to engender its successor. Much in the argument is reminiscent of the traditional Aristotelian proof; but there is this difference, which makes it clear that the new argument is only another version of the first: What needs explanation is not merely the existence of a contingent being or of a thinking being but of “a being which thinks and which has some idea of God.” Thus, the principle that there must be at least as much reality in the cause as in the effect precludes the possibility that any being less perfect than God could have created Descartes—or any person.

This argument is of scarcely more than historical interest. The same is true of the argument from the Fifth Meditation that, since existence is a perfection, the idea of a Perfect Being entails...

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Knowledge of the World

Much of the rest of Meditations on First Philosophy is devoted to determining just how far people can trust the faculties that the beneficent Deity has implanted in them. First, one must distinguish between impulses that incline one to belief (such as “the heat that I feel is produced by the fire”) and insights into necessary truths (such as “a cause must be as great or greater than its effect”). Both are natural, and owing to the good offices of the Creator. However, the former can be doubted, even after one has discovered the truth about God; the latter, which Descartes speaks of as “the light of nature,” cannot be doubted at all. They are the principles of reason in our minds by which we arrive at knowledge. One has no other means of distinguishing between true and false.

Second, one must consider the causes of error. It is axiomatic that God can never deceive people and that if they make proper use of the abilities received from the Deity, they can never go wrong. Yet obviously, God has chosen to make people fallible. This situation arises from the fact that the intellect is finite, together with the fact that the will is infinite. One can see why both these things must be and how, as a consequence, people do not easily stay within the narrow realm of truth. The crux of the matter is that, for Descartes, judgment involves the will (in the form of “assent” or “dissent”). It is within people’s power to withhold judgment when convincing evidence is wanting and to give it only when the light of reason demands. Indeed, Descartes held that people have a duty to bring judgment under this rule. Failure to do so involves not merely error but sin.

Third, one’s knowledge of the external world creates a number of problems. Descartes examined a piece of wax to find what constitutes the essence of matter. He observed that the sensible qualities that people most readily believe to be in matter are not part of the nature of wax, as are such attributes as...

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(Student Guide to World Philosophy)

Additional Reading

Chappell, Vere, ed. Descartes’s Meditations: Critical Essays. Lanham, Md.: Rowman and Littlefield, 1997. A significant collection of essays by scholars who carefully assess the perspectives and problems in one of Western philosophy’s most important texts.

Copleston, Frederick. A History of Philosophy: Modern Philosophy. Garden City, N.Y.: Doubleday, 1964. Copleston situates René Descartes in the history of philosophy with an accessible discussion of Descartes’s major theories.

Cottingham, John, ed. The Cambridge Companion to Descartes. New York:...

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