Meditations on First Philosophy (with Objections and Replies) | Study Guide

René Descartes

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Meditations on First Philosophy (with Objections and Replies) | Main Ideas



Doubt is the method according to which the Meditations are structured. As the Meditator doubts, all ideas become suspect. The only way to move forward is to find an idea that cannot be doubted. Since this process could conceivably go on for an interminably long time, were the Meditator to examine each idea individually the method proceeds by assuming all ideas are false. If there is one idea that is impossible to doubt—maintaining its falsity generates a contradiction—then the idea must be true.

Doubt is also a significant element of Descartes's argument for reason as the source of scientific knowledge rather than sense perception. Doubting is a fundamentally rational enterprise. After all sensation merely provides information. It does not organize or evaluate it.

The method of doubt is used in arguments throughout the Meditations, but particularly in the first three. There doubt leads the Meditator to:

  • reject the senses as reliable;
  • consider the possibility that an evil genius deceives him;
  • arrive at the certainty of the "I think" (the Cogito);
  • conclude that the mind is better known than the body;
  • reject the possibility that God is a deceiver.

Mind/Body Distinction

By arguing for the position that mind and body are distinct substances, Descartes makes room for truths of religion and science. Religious truths concern the mind (or soul), while scientific truths concern the material world. Descartes's argument for the distinction between mind and body begins in the Second Meditation, resumes in the Fifth, and is completed in the Sixth. The distinction itself has vexed thinkers for centuries, and Descartes's solution to the problem of how two metaphysically distinct substances can interact has exasperated many for its woeful inadequacy.

Descartes holds that the mind and body are distinct substances. The mind is a thinking, nonextended substance, while the body is a nonthinking extended substance. This essential difference means that each can exist without the other, which suggests science and religion are compatible, but it also profoundly complicates any explanation of their causal interaction.

God, Existence, and Substance

God is the metaphysical and epistemological lynchpin in Descartes's philosophical structure. It is God, after all, that guarantees the possibility of certain knowledge. The way Descartes validates knowledge demands God as the perfect creator. By guaranteeing his judgments can be correct, God makes it possible for the Meditator to move "outward," from the subjective isolation of his mind to the external world.

God is an immaterial, infinite substance—the only one of its kind. According to Descartes, each substance has a principal attribute, or essence. God's essence is perfection. The mind is also immaterial and unextended, but it is finite. Its essence is thought. The body is the sort of substance that is material and extended. Its essence is extension. By arguing for distinct substances, Descartes makes possible the mind/body distinction.

Descartes distinguishes—in the case of mind and body—essence and existence. The existence of bodies is doubted until the Sixth Meditation, although the essence of body is uncovered in the Second Meditation and confirmed in the Fifth. The existence of mind is (indirectly) doubted until the beginning of the Second Meditation, and when it is established, so also is its essence. (The essence of the "I" is thinking, and since thinking is impossible without existence, it is possible that existence disappears when thinking stops.) God, on the other hand, is the supremely perfect being. It is impossible, therefore, to separate his existence from his essence, since, as a perfect being, God necessarily exists.

Clear and Distinct Ideas

When the Meditator has determined the certainty of his existence as a thinking thing and is also certain he can make errors of judgment, he needs a rule or standard by which to continue making progress in his meditations. This rule is discovered by an analysis of what it was about the Cogito (the "I think") that made it indubitable. The act of thinking, "I am, I exist," he realizes, involved "nothing other than a clear and distinct perception of what I affirm to be the case" (Third Meditation).

Although he does not provide an explanation of what a clear and distinct idea is, the reader can make some promising inferences from the passage in which the Cogito occurs. First, there is a sequence of elimination leading up to it. On the assumption that all his ideas are false, it follows that everything his senses present to him is not real, both at the present and in the past. The senses themselves do not exist. Thus his body and the world in which it lives cannot exist either. Perhaps "some God" makes him think as he does, or perhaps he is the author of his own thoughts. If so, then it follows he exists, but it is not clear how, since he just denied he has a body. Even still he could exist without a body. Indeed, since he just convinced himself of something—namely, that he does not exist—then, even without a body, he exists. This is not certain, however, since it is possible a deceiver (and evil genius) is purposefully and continuously deceiving him. Here, however, he finds certainty: if he is deceived, he must exist.

This process is one of reduction to a contradiction: the Meditator both exists (he is deceived) but does not exist. It is self-evident, according to Descartes, that thinking is a mode of existence.


The dream sequence in the First Meditation highlights the dubiousness of sense perception as a standard of knowledge. If the Meditator claims to know that a proposition is true because his sense perception told him, then if his sense perception is unreliable, he cannot properly be said to know with any certainty. Suppose he says he was swimming in the ocean because he felt the cold water on his skin and also tasted its saltiness, but then it turned out he was dreaming of swimming. The sense perceptions are the same in either case, waking or dreaming. They cannot, therefore, be a reliable indicator of which state the Meditator is in, and which claims are true and which are false. And for the same reason, the senses also cannot be used to distinguish dreaming from waking states.

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