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Write-up2 (as at 22/07/2010 20:12:29): Descartes - Real Distinction
What is Descartes’s argument for the ‘real distinction’ between mind and body? Is it a good one?
In this essay3, I consider two suggestions in the literature for Descartes’s Real Distinction argument. The first, the Modal Argument, is expounded by "Wilson (Margaret) - Descartes". The second, which I will term the Two-Substance Argument, is scattered throughout Descartes’s oeuvre and is expounded by "Rozemond (Marleen) - The Real Distinction Argument". In addition, I consider some objections to Descartes, together with his replies.
The Modal Argument
The Modal Argument is best explained by the following text from the Sixth4 Meditation:
How does this argument work? Using the above numbering, Descartes’s first major premise is (1) that anything that he clearly and distinctly understands can be brought about by God. So, if (2a) he can clearly and distinctly understand one thing apart from another, (2c) God can (by (1)) separate them. Descartes’s second major premise is that if (by 2(c)) two things can exist apart, then (2b) they are really distinct. Finally, he claims (6) that he can clearly understand mind separated from body (himself as thinking, but lacking the principal attribute of body, namely extension), and (7) vice versa, so satisfying (2a) for mind and body. Consequently, by (1), God can separate them, giving (2c), though (3) the manner whereby he does this is irrelevant. The fact that, as things stand, (5) Descartes’s mind and body are closely joined is irrelevant to the argument, which deals in conceptual possibilities. Thus, given (2a) and (2c), we have (2b), for mind and body, which are really distinct, giving (8) in which by “I” Descartes means, from (4), his mind.
- “First, (1) I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly with my understanding of it. Hence the fact that (2a) I can clearly and distinctly understand one thing apart from another (2b) is enough to make me certain that the two things are distinct, since (2c) 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. Thus, (4) simply by knowing that I exist and seeing at the same time that absolutely nothing else 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. But nevertheless, (6) 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 (7) on the other hand I have a distinct idea of body in so far as this is simply an extended, non-thinking thing. And accordingly, (8) it is certain that I am really distinct from my body, and can exist without it.”
The Two-Substance Argument
Rozemond summarises her version of the Real Distinction Argument on p.35. She rejects the Modal Argument, claiming that mind and body are really distinct not because they are conceptually separable but because they are different substances. Of course, Descartes agrees that mind and body are conceptually separable, thinking them actually separable in order to maintain the orthodox Catholic doctrine of the immortality of the soul. However, according to Rozemond, this separability is a consequence of the real distinctness, rather than the reason for it.
So, to prove:
Descartes’s major premise is:
- (a) Mind is really distinct from body,
Hence, Descartes needs to prove:
- (b) Different substances are really distinct.
To prove (c) we need:
- (c) Mind and body are different substances.
… Leibniz’s Law, and
- (d) The substance that is the subject of thoughts (mind) is not extended,
Proving (d) also requires (e), together with the Attribute Premise:
- (e) Body is a substance whose principal attribute is extension.
- (f) A substance has exactly one principal attribute,
To prove (g) by modus ponens, Descartes needs:
- (g) Thought is a principal attribute distinct from extension.
- (h) If thought is not a mode of extension, then it is a principal attribute distinct from it.
Finally, to prove (i) we need to know when one property is not a mode of another:
- (i) Thought is not a mode of extension.
Consequently, (i) follows from (j), taking phi as thought and psi as extension, given:
- (j) We can tell that some intrinsic property phi is not a mode of some other intrinsic property psi if, when we are certain that something is phi we can doubt that it is psi.
Several premises weren’t justified in the course of the argument. We don’t have space to provide full justification, so a few animadversions will have to suffice.
- (k) Descartes is certain that he thinks, but can still doubt that he is extended.
- (b) is true by definition, because Descartes differentiates between Real, Modal and Conceptual5 distinctions. Real distinctions only exist between different substances6. Modal and Conceptual distinctions need not detain us.
- (e) is clearly something Descartes argues for elsewhere (eg. Principles, Section 537).
- Rozemond admits that Descartes does little to motivate and nothing to justify (f), but that he holds it is also seen from Principles, Section 53. The principal attribute defines what sort of thing the substance is, all the other intrinsic properties of that thing being modes of the principal attribute.
- (h) seems justified because if thought is not a mode of extension, then it must either be a mode of some other principal attribute, or itself a principal attribute.
- (j) depends on the truth of clear and distinct ideas, but also on Descartes’s belief that when we clearly and distinctly consider an attribute and one of its modes together, we cannot doubt that the mode depends on its attribute8.
- (k) is covered by premise (4) of the Modal Argument.
Is the Real Distinction Argument a Good One?
- It has been suggested that all Descartes’s Modal Argument shows is that mind and body could possibly have been distinct, had God chosen to make them so, rather than that they are in fact distinct. This fundamentally misses Descartes’s point. Descartes holds that two things are distinct if it is possible for them to exist separately. Actual distinctness does not entail actual separateness.
- An immediate response to the Two-Substance Argument is that premise (f) can’t be obvious since Spinoza’s whole system relies on thought and extension being the two principal attributes of the one substance, “God or nature”.
Formal versus Real Distinction
- In the First9 Objection Caterus identifies a problem in the Modal Argument where Descartes reasons from the fact that soul and body are distinctly and separately conceivable to the conclusion that they can exist apart. Caterus points out that only a formal distinction, rather than a real distinction, is required for things to be conceived distinctly and separately from one another. For example, the concepts of justice and mercy are separate so can be conceived of independently, yet that doesn’t imply that God’s justice can exist in separation from his mercy.
- This objection is important because, as Wilson (p.9) points out, Descartes himself holds that “simples” such as extension, shape, motion and duration can, by abstraction, each be clearly and distinctly conceived in themselves, yet denies that they are really distinct, because shape cannot exist without extended body, nor motion without duration10. In this doctrine of simples, Descartes is opposed to the principle that what can be clearly and distinctly conceived separately can exist separately.
- Descartes’s response11 is that a formal distinction applies only to incomplete entities, which he claims accurately to have distinguished from complete entities. For things to exist separately, they need to be entities in their own right, and a real distinction is required for this. While we can, by intellectual abstraction, distinctly conceive of one of these incomplete entities separately from the other, this is insufficiently distinct and separate for us to understand them as existing as complete entities in themselves.
- Descartes gives his own example. The distinction between the motion and shape of the same body is a formal one. While I can understand the shape apart from the motion, and vice versa, each abstracted from the body, yet I cannot understand motion completely apart from the shape whose motion it is.
- Descartes contrasts his and Caterus’s examples of incomplete beings with the mind-body case. He claims that he can understand body as a complete thing by merely thinking of its extension, shape, motion and so on, quite apart from anything pertaining to a mind. Similarly, he can understand the mind as a complete thing that doubts and suchlike, while denying it anything contained in the idea of body.
- In summary, Descartes can conceive body and mind not only distinctly, but as complete things while simultaneously denying of each what belongs to the other. Justice and motion, however, while they can be understood distinctly in separation from mercy and shape, cannot be understood as complete things.
- Descartes hadn’t explicitly included this distinction in the Modal Argument. Consequently, premise (6) needs to be modified to claim that he has a clear and distinct idea of himself as a complete thing.
- Another common objection is that Descartes’s Modal Argument rests on the unfortunate fact that if one is sufficiently ignorant, one can conceive almost anything. However, being able to conceive that p doesn’t even entail the possibility of p; at best all that follows is that one hasn’t yet found p to involve a contradiction.
- This leads us to Arnauld’s claim, in the Fourth12 Objections that Descartes cannot conclude that extension doesn’t belong to his essence merely because he notices nothing else essential to his nature besides thought. Maybe his conception of himself is inadequate and he perceives only part of his essence in conceiving of himself as a thinking thing. This objection attacks both formulations of the Real Distinction Argument. Arnauld13 adduces the case of someone who clearly and distinctly conceives of a triangle as right-angled, yet is ignorant of Pythagoras’s theorem which, because of his incomplete knowledge of the triangle, he is able to deny. Consequently, he might claim that, since the clear and distinct idea of a right-angled triangle doesn’t include the notion of Pythagorean proportions, God might have caused some other relation between the sides to obtain. Since this conclusion is false, the Modal Argument must be invalid, since it uses the same pattern of argument.
- Descartes’ response14 is that he’s proved that God can do all that Descartes clearly and distinctly knows to be possible. Consequently, even though in the Second Meditation he’s willing to concede there’s much in him existing unnoticed, since what he does notice is sufficient alone for him to constitute a complete thing, he’s sure that God could have created him without these presently unnoticed attributes. Hence, these other attributes can be judged not to belong to his essence since no property that a thing can exist without is comprised in its essence.
- Descartes admits15 that, in responding to Caterus, he had claimed “complete knowledge”, which he meant to be equivalent to knowledge of a complete thing. He did not mean adequate (ie. exhaustive) knowledge, which usually only God has and even if we have it, we cannot know we do. He meant sufficient knowledge of a thing to know it is complete, with sufficient attributes for him to recognise it as a substance.
- Descartes rejects16 Arnauld’s example of the triangle both because the Pythagorean ratio is not a “complete thing” but also because we don’t distinctly understand a triangle if we don’t understand the relationship between the squares of its sides. So, the supposed analogy with mind and body fails.
- Both arguments rely on the existence of God, and therefore on Descartes’s dubious proofs in the Third and Fifth Meditations. God plays two roles in the Real Distinction arguments. Firstly, in the Modal Argument, to bring about what Descartes clearly and distinctly perceives to be possible. Secondly, in both arguments, to guarantee that Descartes’s clear and distinct perceptions are true.
- The Modal Argument can be repaired in modern guise by replacing references to “God” with “logically possible worlds”. For instance, we could say that “Whatever I can clearly and distinctly understand can be true in some logically possible world just as I understand it”, rather than “…brought about by God …”.
- However, God cannot be so easily excised from his role in validating the truth of Descartes’s clear and distinct ideas, which are needed passim in the Modal17 Argument, and at least at step (j) in the Two-Substance Argument. As Descartes states in the Fourth Replies18 the reason he deferred the Real Distinction Argument from the Second to the Sixth Meditation is that, since the Meditations seek metaphysical certainty rather than mere moral certainty, he needs a veracious and benevolent God who would not allow him to go astray in the things that seem most self-evident.
- In the Fourth Meditation, Descartes claims19 that God has given him a faculty of judgement which, since God is no deceiver, won’t allow him to go wrong while using it correctly. Descartes concludes20 that it’ll be impossible for him to err if he restrains his will from extending further than what his intellect clearly and distinctly reveals.
- Without some reason for believing that what I can clearly and distinctly perceive is certain, and doesn’t contain some hidden contradiction, the arguments won’t go through. Descartes argues all will be well if we don’t overstep the mark and inquire into things for which our intellect is not suited, but if we’re unimpressed by such arguments, we have no such reason.
- Which of the two arguments should we prefer? Effectively, the Modal Argument says that mind and body are different substances because they are distinct (because a complete thing is a substance21) whereas the Two-Substance Argument says that they are distinct because they are different substances.
- The Two-Substance Argument has no advantages over the Modal Argument because it also relies on the validation of clear and distinct perceptions. Since it additionally introduces the dubious single-attribute premise, it is not to be preferred.
- The Real Distinction Argument in either form is only as good as the distinction between clear and distinct conceptions and mere conceptions. This reliance on the identifiability of clear and distinct ideas and their ontological consequences is in the end fatal.
Footnote 3: Written in March 2004 as a pre-submission for my BA Finals
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Footnote 4: CSM.II.54.
CSM.II = "Descartes (Rene), Cottingham (John), Stoothoff (Robert), Murdoch (Dugald) - The Philosophical Writings of Descartes Vol II".
Footnote 5: Principles Sections 60-62. CSM.I.213-4.
CSM.I = "Descartes (Rene), Cottingham (John), Stoothoff (Robert), Murdoch (Dugald) - The Philosophical Writings of Descartes Vol I".
Footnote 6: Section 60
Footnote 7: CSM.I.210.
Footnote 8: Rozemond discusses this issue on p.16, and quotes a letter of Descartes’s to Gibieuf (CSMK.202) in support.
CSMK = "Descartes (Rene), Cottingham (John), Stoothoff (Robert), Murdoch (Dugald), Kenny (Anthony) - The Philosophical Writings of Descartes Vol III - The Correspondence".
Footnote 9: CSM.II.72-3.
Footnote 10: Rules for the Direction of the Mind, CSM.I.45-6. Eg. “… we cannot conceive of a shape which is completely lacking in extension …”.
Footnote 11: First Replies, CSM.II.85-6.
Footnote 12: CSM.II.140-1.
Footnote 13: CSM.II.142.
Footnote 14: Fourth Replies. CSM.II.154-5.
Footnote 15: CSM.II.156.
Footnote 16: CSM.II.158-9.
Footnote 17: Explicitly at steps (1), (2a), (6) and (7).
Footnote 18: CSM.II.159
Footnote 19: CSM.II.37-8.
Footnote 20: CSM.II.43.
Footnote 21: CSM.II.156, as discussed above under Incomplete Knowledge .
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