The Fifth Meditation opens with the Meditator turning his attention toward material objects. Rather than inquire into the things themselves, he inquires into her ideas regarding material things. He concludes that he can distinctly imagine extension, size, shape, position, and local motion, which is associated with duration.

The Meditator also considers that there are abstract geometrical objects which do not exist in the material world, do not depend on her mind, yet are not nothing. For instance, there are no triangles in the world, yet they have some kind of being. Even if no triangle has ever existed anywhere outside the mind of the Meditator, triangles still have a determinate essence which is independent of the Meditator's mind. The Meditator also denies that he has come to know the nature of triangles through the senses. After all, he can think up all sorts of shapes that he has never seen and derive their properties as clearly and distinctly as he does with those of the triangle. These properties must all be true since the Meditator clearly and distinctly perceives them. Besides, he notes, even before he began to doubt, he always regarded mathematical and geometrical objects as more certain than the objects of the senses.

The Meditator has reasoned that a triangle must have all the properties he ascribes to it, because the triangle exists as an idea in his mind and he clearly and distinctly perceives all these properties. He then reasons by analogy that God exists as an idea in his mind and he clearly and distinctly perceives all of his qualities. One of these qualities is existence, so it follows from his clear and distinct perception that God must exist. If existence is the essence of God, then God would not be God if he did not exist, just as a triangle would not be a triangle if it were not three-sided. At the very least, then, the existence of God must be as certain as the properties of mathematical and geometrical objects since he can prove them in the same way.

Clear and distinct perceptions are always convincing, according to the Meditator. Some perceptions may be evident, like the fact that a triangle has three sides, and some may take more thought, like the Pythagorean theorem that states that the sum of the squares of the legs of a right triangle is equal to the square of the hypotenuse. But once the Pythagorean theorem is proved, it is just as certain as any other clear and distinct perception. Similarly with God: his existence would immediately be perceived clearly and distinctly if it weren't for the confusions caused by the senses and preconceived opinions. Now that God's existence has been established, it is as certain as any other clear and distinct perception.

The Meditator asserts that God is the guarantor of his clear and distinct perceptions. He admits that he cannot constantly fix his mental vision on any particular perception, so that there might be times when he is not clearly and distinctly perceiving a certain truth. At such times, doubt could creep in, if not for God. Because he knows that God is not deceiving him and has endowed him with a faultless understanding and a will than cannot but assent to clear and distinct perceptions, he knows that what he clearly and distinctly perceived in the past is and remains true even if he is not currently directing his mental vision toward it. Those judgments about which he is mistaken are not clearly and distinctly perceived by the intellect. And even if he is dreaming, as was suggested in the First Meditation, he cannot be mistaken with respect to a clear and distinct perception.


"Essence" is one of those philosophical terms thats currency has waned a bit since the seventeenth century. The essence of a thing is the property or set of properties that the thing cannot do without. For instance, Aristotle defines rationality as an essential characteristic of a human being. A person could lose a leg and still be human, but a person could not cease to be rational and remain human.

Descartes' discussion of essence is intended as a strong reaction against Aristotelian empiricism. According to Aristotle, we learn the essence of, say, a triangle, by examining instances of triangular-shaped objects in the world and extracting the essence of triangles from these worldly instances. Descartes turns this formulation on its head, saying that we learn the essence of a triangle solely through the intellect, and only afterward do we look at the real world and see if there are instances of triangles. In Descartes' formulation, whatever properties of a thing that we clearly and distinctly perceive must be essential. Thus, bodies are essentially extended, since extension is clearly and distinctly perceived by the intellect prior to any empirical investigation. The essence of body will be further discussed in the Sixth Meditation.

Descartes provides strong reasons to support his move against Aristotle. If essences are extracted from the real world, how is it that we understand perfect triangles when there are none? And more importantly, how do we understand abstract shapes that we have derived mathematically but have never encountered in the real world? In Aristotle's defense, however, we could point out that while Descartes has given us a better understanding of the essences of mathematical objects, he has left us completely in the dark as to how we can know the essence of material things. Is it possible to apply the intellect to understanding the essence of, say, gold, without ever encountering gold in the world?

Descartes then turns his discussion of essence toward a second proof of God's existence. This proof is weaker than the one found in the Third Meditation, and we might wonder why he adds it. Is he not certain that his earlier proof is satisfactory? And if so, what holes does this new proof patch up? Most importantly, it reinforces the connection between God and clear and distinct perceptions. Clear and distinct perceptions are made certain because God exists, and God's existence, as an essential property, is clearly and distinctly perceived. Of course, this reinforced connection only reinforces the conundrum of the Cartesian Circle. This problem is discussed in the commentary to the Third Meditation, Part 3.

The proof of God's existence found here is a version of a proof that was popular among the Scholastic philosophers. Our idea of God is the idea of a perfect being, and one of the attributes of a perfect being would be existence, since it is more perfect to exist than not to exist. In Descartes' formulation, existence is not just an attribute, but an essential property of God's, so that God cannot be conceived of without existence. This proof, however, rests on the faulty assumption, first pointed out by Kant, that existence is a predicate or a property, like "being red" or "being tall." In fact, "exists" is a very different kind of predicate than "is red" or "is tall." The predicate "exists" does not modify an object so much as it modifies the world. If I say "the red car exists," the property of redness is something that modifies the car. On the other hand, "exists" does not modify the car so much as it says that the world is such that the car is in it. In that sense, "exists" is not a property of the car's.

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