Framework

Descartes’ Meditations on First Philosophy (1641) is probably the most widely read book of metaphysics ever written, and one of its most widely discussed theses is that the mind is really distinct from the body, and can exist without it. His argument for this thesis has puzzled his readers ever since it was put forward. My aim in this chapter is to elucidate the argument, and to comment on some objections to it.

The translations below are those of the standard edition of Descartes’ philosophical writings in English, referred to as CSM (the translators, Cottingham, Stoothoff and Murdoch), I (vol. 1) and II (vol. 2), and CSMK (the translators, Cottingham, Stoothoff, Murdoch and Kenny) (see Descartes 1984–5, 1991).

The real distinction

Descartes’ argument for the real distinction fi rst appears in rudimentary form in the Discourse on the Method (1637). After arguing that he cannot doubt that he exists, Descartes goes on to say that if it were not for his thinking, he would have no reason to believe that he exists. From this he concludes that his essence consists only in thinking, and that his mind is entirely distinct from his body and would be what it is even if his body did not exist (CSM I 127).

Descartes had invited readers of the Discourse to point out to him anything they found worthy of objection. One of his readers pointed out that from the fact that Descartes does not perceive himself to be anything other than a thinking thing it does not follow that his essence consists only in his being a thinking thing. Descartes replies that in the passage in question he was not intending the exclusion indicated by the word “only” to apply to how things are in reality, but only to how they are in his perception of them. In the Meditations, however, he undertakes to show how, from the fact that he is not aware of anything else belonging to his essence, it follows that nothing else does in fact belong to it (CSM II 7).

The place in the Meditations where Descartes purports to show how, from the fact that he is not aware of anything else belonging to his essence, it follows that nothing

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else does in fact belong to it, is the following passage in Meditation Six (CSM II 9, 11, 95) (I have added the numbers in the following [passage A] for the sake of reference).

[1] First, I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly with my under-standing of it. [2] Hence the fact that I can clearly and distinctly understand one thing apart from another is enough to make me certain that the two things are distinct, since they are capable of being separated, at least by God. [3] The question of what kind of power is required to bring about such a separation does not affect the judgement that the two things are distinct. [4] Thus, simply by knowing that I exist and seeing at the same time that absolutely nothing belongs to my nature or essence except that I am a thinking thing, I can infer correctly that my essence consists solely in the fact that I am a thinking thing.

[5] It is true that I may have (or, to anticipate, that I certainly have) a body that is very closely joined to me. [6] But nevertheless, on the one hand I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing; and on the other hand I have a distinct idea of the body, in so far as this is simply an extended, non-thinking thing. [7] And accordingly, it is certain that I am really distinct from my body, and can exist without it.

(CSM II 54)

This passage is puzzling in many ways. The key to understanding it, I believe, lies in the distinction which Descartes makes between the mental acts of abstraction and exclusion (see Murdoch 1993). He does not introduce this distinction explicitly in any of his published writings, but he explicates it in a letter to Gibieuf of 19 January 1642, which he wrote not long after the publication of the Meditations (CSMK 201). In the case of abstraction, Descartes explains, we turn our attention away from a part of the content of a richer idea and focus it on another part. For example, we focus our attention on some shape without thinking of the extended substance whose shape it is. We can tell that this act is an abstraction from the fact that while we can think of the shape without paying any attention to the extended substance, we cannot deny the one of the other when we think of them both together, that is, we cannot think of the shape and at the same time deny that it has an extension, and we cannot think of the extension and at the same time deny that it has a shape. In the case of exclusion, by contrast, we focus our attention on the contents of both ideas while denying the one of the other.

For example, we focus our attention on a thinking substance and on extension while denying that the thinking substance is extended or that extension is a thinking substance. We can tell that this is an act of exclusion by the fact that we can deny the one of the other. We can deny the one of the other because we recognise that no contradiction is involved in the denial.

Passage A should be understood in terms of exclusion, not abstraction. When Descartes says in sentence (2), “I can clearly and distinctly understand one thing apart from another,”

what he intends is an act of exclusion. It is not that Descartes can clearly and distinctly understand the one thing while not attending to the other thing, but that he can clearly

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and distinctly understand the one thing while denying the other thing of it. When he says in sentence (6), “I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing,” what he intends is an act of exclusion, for he is conceiving of himself as a thinking thing while denying of himself that he is extended.

The importance of exclusion for Descartes’ reasoning in passage A is emphasised in a letter which he wrote to Mesland on 2 May 1644:

There is a great difference between abstraction and exclusion. If I said simply that the idea which I have of my soul does not represent it to me as being dependent on the body and identifi ed with it, this would be merely an abstraction, from which I could form only a negative argument, which would be a poor result. But I say that this idea represents it to me as a substance which can exist even though everything belonging to the body be excluded from it;

from which I form a positive argument, and conclude that it can exist without the body. (CSMK 236; I have altered the CSMK translation at “which would be a poor result”)

By “a negative argument” Descartes means that the conclusion would be “I do not know that the mind is dependent on the body,” and by “a positive argument” he means that the conclusion would be “I know that the mind is not dependent on the body.”

Exclusion is crucial for Descartes’ reasoning in passage A, for it is thanks to exclusion that Descartes’ understanding of himself simply as a thinking thing is clear and distinct.

A perception, in the generic sense which covers conception, understanding, recog-nition, and perception in the specifi c sense, is clear when it is “present and accessible to the attentive mind,” and distinct when, as well as clear, “it is so sharply separated from all other perceptions that it contains within itself only what is clear” (CSM I 207–8). His perception of himself simply as a thinking thing is clear, because it is present and accessible to his attentive mind, and it is also distinct, because it is sharply separated from his perception of every other thing. What makes it thus sharply separated is Descartes’ act of exclusion. While understanding himself as a thinking thing, he can, without self-contradiction, deny of himself every attribute other than that of thinking and the modes of this attribute, such as perception and willing. It is his ability to make this denial which makes his understanding of himself simply as a thinking thing distinct as well as clear, and which entails that his understanding of himself simply as a thinking thing is not a mere abstraction; if it were a mere abstraction, then for all he would know, he might be essentially extended.

It may seem from passage A that Descartes’ knowledge that he, a thinking thing, is really distinct from his body, and can exist without it, depends entirely upon the power of God to separate him from his body. But this is not the case, as is shown by sentence (3), where he says, “The question of what kind of power is required to bring about such a separation does not affect the judgement that the two things are distinct.” Descartes makes the same point again at the end of the First Replies, where he says, “Our knowledge that two things are really distinct is not affected by the nature of the power that separates them” (CSM II 120). What he means by this is, I believe, as follows.

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The fact that Descartes has a clear and distinct understanding of himself simply as a thinking, non-extended thing is suffi cient for him to know that he is a thinking, non-extended thing, and hence distinct from his body; this is suffi cient, because whatever we clearly and distinctly understand is true in a way which corresponds exactly to our understanding of it (Synopsis, CSM II 9). Descartes had introduced the latter thesis (call it “the truth thesis”) at the beginning of Meditation Three (CSM II 24), and proved it to his satisfaction in Meditation Four (CSM II 41–3).

However, the fact that Descartes is distinct from his body does not entail that he is really distinct from his body, that is, that he can exist without it (as Wilson notes [1978: 190]). It may be that although Descartes is distinct from his body, his existence depends upon his body, owing to some close connection between himself and his body. There seems to be just such a close connection, as he observes in sentence (5) of passage A, and consequently some power may be required to break the connection if he is to exist without his body. There is a power capable of breaking this connection, namely, God’s power. Hence Descartes is really distinct from his body, and can exist without it. This is not to say that God’s power is necessary to break the connection, for as Descartes says at the end of the Second Replies, he introduced the power of God not because some extraordinary power was needed, but because in the preceding arguments he had dealt only with God, and hence there was no other power he was aware of (CSM II 120).

The present interpretation is supported by what Descartes says in the letter to Gibieuf cited above. He states there that there can be no such thing as an atom, an extended thing which is indivisible, because it is impossible to have an idea of some extended thing without having the idea of half of it, or a third of it, and so on, and hence the thing in question is in reality divisible, since God has given Descartes the faculty of conceiving it as divisible. Someone might object that from the fact that Descartes can conceive of the parts it does not follow that they are separable, since God may have joined them so tightly together that they are completely inseparable. To this, Descartes replies that in that case, God can separate them. He adds, “so that absolutely speaking I have reason to call them divisible, since he has given me the faculty of conceiving them as such.” The same holds, he says, where the mind and the body are concerned (CSMK 202–3). In light of this, it is clear that Descartes’ knowledge that he is really distinct from his body depends primarily on the truth thesis, and only secondarily on the power of God to separate him from his body.

The argument for the real distinction can be set out as follows:

(1) Whatever I clearly and distinctly understand is true.

(2) I clearly and distinctly understand myself as a thinking, non-extended thing.

(3) Therefore I am a thinking, non-extended thing.

(4) Therefore I am distinct from my body.

(5) Yet some power may be needed to separate me from my body.

(6) There is such a power, namely, God’s power.

(7) Therefore I can exist without my body.

(8) Therefore I am really distinct from my body.

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Descartes gives a second argument for the distinction between the mind and the body in Meditation Six, which is that the mind is indivisible, whereas the body is not (CSM II 59). When Descartes considers the mind, he cannot distinguish any parts, whereas when he considers the body, he can. Modes of thinking, such as perceiving and willing, understanding and denying, and so on, are not parts of the mind, for it is one and the same mind which perceives and wills, understands and denies, and so on. This one argument, Descartes says, would be enough to show that the mind is completely different from the body if he did not know this from other considerations (what he is alluding to here is the argument of passage A). Exclusion plays a tacit role in this second argument, for Descartes must be assuming here that when he considers the mind, his conception of it is formed by exclusion, and not by abstraction from the richer idea of a single substance which is both thinking and extended, for if it were so formed, he could not be certain that the mind has no parts.

The role of exclusion in Descartes’ “Replies”

The notion of exclusion plays a crucial role in Descartes’ replies to his critics in the Objections and Replies, though he does not employ the term “exclusion” there. For example, the author of the First Objections, Caterus, objects that to understand one thing apart from another there need not be a real distinction between them; it is enough that there should be a formal distinction (CSM II 72). Descartes replies that a formal distinction is what he calls a modal distinction. A modal distinction is a distinction either between an attribute and a mode of that attribute or between two different modes of an attribute. In the case of a modal distinction we can understand the one item apart from the other by abstraction, but not by exclusion. We can understand the shape of a body apart from its motion, and vice versa, but we cannot deny that the body which has that shape has some motion or other, and we cannot deny that the body which has that motion has some shape or other. This shows that the distinction between the shape and the motion is not real, that the one cannot exist without the other. In the case of the mind and the body, by contrast, we can understand the mind as a thinking thing while denying that it is extended, and we can understand the body as an extended thing while denying that it is thinking. These denials would not be possible if there wasn’t a real distinction between the mind and the body (CSM II 85–6; see also CSM II 213–14).

The author of the Fourth Objections, Arnauld, had read Descartes’ Replies to Caterus, and in light of his reading he puts forward the objection that although Descartes can deny that the mind is extended, he may be mistaken in doing so, for by the same token someone could clearly and distinctly understand that a triangle inscribed in a semicircle was right-angled yet mistakenly deny that the square on the hypotenuse was equal to the sum of the squares on the other two sides (CSM II 141–3).Descartes replies that the said person does not distinctly understand that the triangle is right angled, for there is no way in which this person could distinctly understand that the triangle is right-angled and at the same time deny that the square on its hypotenuse is equal to the sum of the squares on the other two sides. This person’s understanding of the triangle is not distinct, but confused (and, we should add, could be shown to be confused) (CSM

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II 158–9). Descartes makes essentially the same point in the First Replies, where he says that even if he can understand what a triangle is if he abstracts from the fact that its three angles are equal to two right angles, he cannot deny this property of the triangle by a clear and distinct act of the intellect, that is, while understanding what he means by his denial (CSM II 84).

The role of exclusion in other key arguments in the Meditations Exclusion plays a crucial part in other key arguments in the Meditations, such as the argument for Descartes’ existence in Meditation Two. Descartes is supposing there that his former beliefs are all false, but while supposing this, he recognises that he cannot suppose the thought “I exist” to be false. In other words, he cannot deny “I exist.” His reasoning can be formulated as a classical reductio ad absurdum argument:

(1) I do not exist. (supposition)

(2) I am trying to suppose premiss (1). (beyond doubt) (3) I do not exist and I am trying to suppose premiss (1). (from [1] and [2] by

“and” introduction)

(4) Conclusion (3) is absurd. (beyond doubt)

(5) I exist. (from [1] to [4] by

classical reductio)

This formulation captures the part which exclusion plays in Descartes’ reasoning, for what Descartes is trying to do in line (3) is to perform an exclusion, and what he recog-nises in line (4) is that he cannot perform the exclusion and at the same time under-stand what it is he is doing.

Exclusion plays a crucial part also in Descartes’ argument in Meditation Two that he is a thinking thing. Now that Descartes is certain that he exists, he goes on to ask what he is. He considers the attributes which he formerly ascribed to himself, and rejects those which presuppose the existence of the body, for at this stage he is still supposing that no body exists. At last he hits upon an attribute which he is unable to suppose he does not possess: “Thinking? At last I have discovered it – thought; this alone is insep-arable from me” (CSM II 18). Thinking is insepinsep-arable from Descartes in the sense that he cannot deny “I am thinking.” His reasoning, again, can be formulated as a classical reductio argument.

(1) I am not thinking. (supposition)

(2) I am trying to suppose premiss (1). (beyond doubt) (3) I am not thinking and I am trying to suppose premiss (1). (from [1] and [2] by

“and” introduction)

(4) Conclusion (3) is absurd. (beyond doubt)

(5) I am thinking. (from [1] to [4] by

classical reductio)

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In concluding here that he is thinking, Descartes is not concluding that thinking is essential for his existence, but only that thinking is the only attribute which he knows for certain he possesses. This is shown by his statement that “it could perhaps be that were I totally to cease from thinking, I should totally cease to exist.” He is saying, in other words, that if he were to cease from thinking, he might cease to exist, not that he would cease to exist.

Exclusion is at work also in Descartes’ argument for the existence of God in Meditation

Exclusion is at work also in Descartes’ argument for the existence of God in Meditation