Descartes’ Metaphysics of Nature and Mind—The Sixth Meditation (Part II)

We now come to that doctrine for which Descartes is most famous, or perhaps infamous, certainly in the minds of many today. This is his conviction that the mind is not, as Aristotle thought, merely the form of the body, but in fact a separable existent: precisely because and to the extent that he is a thinking thing, Descartes is not identical with his body but rather is nothing more than his mind. His mind is thus an entity distinct from his body, not just in the sense that it can be distinguished from the latter (as the shape of Arnold Schwarzenegger can be distinguished from him but cannot separated from him¹), but in the sense that it exists potentially and indeed after death actually separate from his body. The claim that Descartes is nothing more than a mind and that this mind can exist separately from the body to which it must therefore be, in a sense yet to be explained, attached is the basis upon which Descartes is described as a substance dualist: he thinks that there are two basic kinds of substance, whereby what distinguishes one kind of substance from the other is a certain defining attribute. In the case of minds, this defining attribute is thinking, in the case of material things, this attribute is extension.²

Descartes’ substance dualism has been the target of much criticism. It is fair to say that the majority of contemporary philosophers reject any form of dualism out of hand. There are some exceptions and some of you will have already encountered one of them last semester, namely, Karl Popper. There are others, too, for example, Sir John Eccles, who wrote the book The Human Psyche (Berlin, Heidelberg and New York: Springer Verlag, 1980). Perhaps the most interesting discussion and defence of dualism is provided by the early twentieth century philosopher Charles Dunbar Broad (1887-1971) in his famous book The Mind and Its Place in Nature (London: Kegan Paul, Trench, Trubner and Co., 1947), which has gone through several editions and derives from his Tanner lectures of 1923. This book, although complicated, is still worth studying. Admittedly, the dualism Broad defends is not strictly a substance dualism of the kind endorsed by Descartes. Rather it is what is known as a property dualism.³ I will eventually distinguish between these two kinds of dualism. But before I get to this, I need to discuss Descartes’ argument for substance dualism—his argument that mind and body are potentially separate entities—and the problems which this position engenders.

§ 1: Descartes’ Argument for the Separability of Mind and Body

How does Descartes get to the conclusion that his human mind is a separable existent with a defining attribute (thought) which distinguishes it from all material things? He knows very well that he cannot assert this claim merely on the basis of the results reached in the First and Second Meditations: thus, in the Preface to the Reader he harks back to his earlier work, the Discourse on Method of 1637, and says that there had only been two objections of any worth raised against this work.

The first objection is: from the fact that the human mind reflecting on itself does not perceive itself as anything other than a thinking thing, it does not follow that its nature or essence consists merely in the fact that it is a thinking thing, where the word ‘merely’ excludes everything else that might also be said to belong to the nature of the soul. I reply to this objection that, in that context, I did not wish to exclude other things with respect to the truth of the question (which I was not discussing at that staged but merely with respect to my own perception. Thus what I meant was: I did not discover anything clearly that I knew belonged to my essence except that I was a thinking thing or a thing that possesses in itself a thinking faculty. I will show below how, from the fact that I do not know anything else that belongs to my essence, it follows that nothing else does in fact belong to it. (p.12)

This is, of course, precisely the point that the argument of the First and Second Meditations shows only that he exists as at least a thinking thing, not that he can exist as at most a thinking thing. In the Second Meditation the possibility has not been ruled out that he has certain features over and above his character as thinking which, on the one hand, he cannot know himself clearly and distinctly, i.e., with certainty, to have, which yet on the other hand he has necessarily, such that he could not exist without them.

But across pp.61-62, a third of the way into the Sixth Meditation and at the end of his recapitulation of the preceding five Meditations, Descartes confidently asserts the following:

(N)ow that I begin to know better both myself and the author of my origin, I do not think that all the things that I seem to acquire from the senses must be accepted with temerity; but at the same time, it is not necessary that all of them be called into doubt.

Firstly, I know that everything that I understand clearly and distinctly can be made by God in the same way that I understand them; therefore it is enough that I can understand one thing, clearly and distinctly, without another in order to be certain that one thing is distinct from the other, because it is possible for them to be separated, at least by God. It is irrelevant by what power the separation is realized in order for them to be considered distinct. Therefore from the fact alone that I know that I exist and that, at the same time, I notice absolutely nothing else that belongs to my nature apart from the single fact that I am a thinking thing, I correctly conclude that my essence consists in this alone, that I am a thinking thing. And although I may (rather, as I shall say soon: I certainly) have a body that is joined very closely to me, since I have on the one hand a clear and distinct idea of myself insofar as I am a thinking) non-extended thing and, on the other hand, I have a distinct idea of the body insofar as it is merely an extended, non-thinking thing, it is certain that I am really distinct from my body and that I can exist without it. (pp.61-62)

Here we have precisely what Descartes has been out to assert all along: the potential separate existence of him himself, as thinking thing, from all material things, in particular, his body. But how exactly Descartes reach this conclusion? Why does he think he is now entitled to move from “I am as at least a thinking thing” to “I exist, at least potentially, as at most a thinking thing”?

In order to understand Descartes’ argument, one needs to understand properly a central claim Descartes makes in formulating it. Descartes says, “I know that everything that I understand clearly and distinctly can be made by God in the same way that I understand them; therefore it is enough that I can understand one thing, clearly and distinctly, without another in order to be certain that one thing is distinct from the other, because it is possible for them to be separated, at least by God.” (pp.61-62) Now there is a danger of misunderstanding this central claim. For one might be led to misunderstand it as indicating that Descartes is simply extending the kind of argument he developed for restoring certainty to his mathematical and perceptual knowledge-claims to claims about what is and is not logically or conceptually possible.

Not infrequently, we make claims such as the following: “It is possible for a dog to have three legs”, “Any magnet necessarily has two poles”, “A bachelor is necessarily an unmarried male”, “There can be no shape which is not the shape of some material thing,”, etc., etc. Such claims as these are what I mean, at least for current purposes, by a conceptual claim. Roughly speaking, in such claims we assert that a certain property F is (or, as in the case of the number of legs possessed by a dog, is not) an essential feature of some kind of thing A. To put the point in an explicitly conceptual way, one might say that in such cases we assert that the concept of being F is implied by, or as is sometimes also said, contained in, the concept of being an A. Now we make such claims on the basis of its seeming clearly and distinctly to us that the relevant claim is true. More precisely, when we claim that it is possible for a dog to have three legs, we do so on the basis of believing ourselves correctly to understand what it is to be a dog. Clearly, it is possible to understand this as a specific case of the general move from “It seems to me clearly and distinctly that p” to “It is actually that p”, whereby in this case “its seeming clearly and distinctly to me” means such things as that I know myself to be able to use the word ‘dog’ correctly in conversation—I do not get continually corrected by my peers—and to have applied it to things indisputably acknowledged to be paradigm cases of doghood, etc. (In other words, all the criteria for genuinely understanding what it is to be a dog, for genuinely possessing the concept of a dog, are fulfilled.)

But perhaps we do not understand this or any other concepts correctly. Perhaps here, too, we need God to act as guarantor, just as He acts as guarantor in the case of mathematical and perceptual knowledge-claiming. In other words, perhaps in order to make the move from the claim, “I can conceive that it is possible for a dog to have three legs,” to the claim, “It is genuinely possible for a dog to have three legs”, I need to know that God exists. Is, then, the argument Descartes has just given to be understood as follows?: Descartes buys into the line of thought just sketched and, having proved the existence of God, believes he may now move from the claim, “It seems to me clearly and distinctly, i.e., under conditions of optimal understanding of the relevant concepts, that I necessarily exist as thinking but I do not necessarily exist as anything else than this, in particular, as embodied” to the claim, “I necessarily exist as thinking but I do not necessarily exist as anything else than this, in particular, as embodied.” In other words, is Descartes arguing as follows?:

1. He can conceive that he might exist, as the thinking thing he is, without a body

2. He now knows God to exist, who would not permit him to be deceived about what is implicit in his concepts, anymore than He would permit Descartes to be radically deceived with his mathematical and perceptual knowledge-claims

∴ He really can exist as a thinking thing without a body⁴

But is this the right way to read the argument Descartes gives at this point in the Sixth Meditation? There are two reasons why this could not possibly be the case. The first reason is as follows: if Descartes believes that even in the case of conceptual knowledge-claiming God is needed as a guarantor of the transition from “It seems to me clearly and distinctly that p” to “It is actually the case that p”, then he is guilty of egregious circularity. Clearly, Descartes has repeatedly appealed to what he understands to be implicit in various concepts. Thus, precisely in his proof of God’s existence he has said, “(I)t is evident to me by the natural light of reason that my ideas are like images of some kind that can easily fall short of the perfection of the things from which they are derived, but they cannot contain something that is greater or more perfect than themselves.” (p.36) This is clearly a conceptual claim and Descartes’ proof of God would be impossible without it. So he cannot coherently think that conceptual knowledge-claiming requires God, or rather knowledge of the existence of God, in order to be rational, hence genuine.⁵

The second reason is the truly decisive one for rejecting this interpretation: it rests on a complete misreading of what Descartes knows with certainty by the end of the Second Meditation. We need to distinguish the following two claims from one another:

A. “I see clearly and distinctly that I necessarily exist as a thinking thing and I see clearly and distinctly that I do not necessarily exist as embodied (as having a body).”

B. “I see clearly and distinctly that I necessarily exist as a thinking thing but I do not see clearly and distinctly that I necessarily exist as embodied (as having a body).”

See “What is Descartes saying in the Sixth Meditation on pp.61-62.pdf,” at the Wattle web site.

The difference between A. and B. lies, of course, in the position of the word ‘not’. Note now that the interpretation just given of what Descartes is arguing at this point in the Sixth Meditation assumes that Descartes is in a position to assert A by the end of the Second Meditation. But this is not so: Descartes is neither in this position nor does he assert anything like this position. Rather, by the end of the Second Meditation he merely asserts the weaker claim B. More accurately, he asserts that although he sees clearly and distinctly that he is as thinking, he does not see clearly and distinctly either that he is, or that he is not, necessarily embodied. He knows he is at least a thinking thing but does not yet know whether his being a thinking thing requires that he be anything more than this, in particular, an embodied, hence material thing.

This suggests how we are to understand Descartes when he says, “I know that everything that I understand clearly and distinctly can be made by God in the same way that I understand them; therefore it is enough that I can understand one thing, clearly and distinctly, without another in order to be certain that one thing is distinct from the other, because it is possible for them to be separated, at least by God”? (pp.61-62) He is precisely not saying what the interpretation just given imputes to him. According to this interpretation he is saying that because he knows God to exist, he knows it is safe to move from “It seems to me clearly and distinctly that, as a thinking thing, I do not need a body” to “It is the case that, as a thinking thing, I do not need a body.” But this is wrong. In fact, Descartes is saying that because he knows God to exist, he knows it is safe to move from “It does not seem clearly and distinctly to me that, as a thinking thing, I need a body” to “It is the case that, as a thinking thing, I do not need a body.” And the underlying idea here is that God created him in such a way that anything logically or conceptually entailed by a concept he possesses and wields correctly is in principle available to him through careful inspection of it. In other words, God has made him such that the content of each and every one of his concepts is accessible to him; there is nothing in any of his concepts which is in principle or ineluctably hidden from his view.

Many commentators on Descartes have observed that he assumes without question the truth of the following principle: if he can conceive that such and such is possible, then such and such really is possible.⁶ Now Descartes certainly does assume and make use of this principle. It is crucial to see, however, that this principle has got nothing to do with what is going on here. If anything, Descartes is here assuming the converse of this principle: if such and such is possible, then he can conceive of it as possible, that is, it can seem clearly and distinctly to him that it is possible. This is the basis upon which he concludes that, given the existence of God, he may now assert that, as a thinking thing, he does not need a body. At the end of the Second Meditation he could only assert that it did not seem clearly and distinctly to him that, as a thinking thing, he needed a body. But he now realises that the existence of (a non-deceptive) God has given him the guarantee not just that he is not deceived in his perceptual experience and mathematical reasoning; it has also given him the guarantee that all the content of his concepts is totally accessible to him. That is, it gives him a guarantee that he can in principle see everything in his concepts, by careful inspection of them.⁷ And so, because he cannot see clearly and distinctly that existence as thinking requires existence as embodied, the accessibility of conceptual content guaranteed by God means he has a certain reason for concluding that existence as thinking does not require existence as embodied, i.e., that his concept of a thinking does not contain or entail the concept of a material thing. Just this is what Descartes is getting at when he says, “(I)t is enough that I can understand one thing, clearly and distinctly, without another in order to be certain that one thing is distinct from the other.” (pp.61-62) It is enough that he sees clearly and distinctly that he exists as thinking without seeing clearly and distinctly that he exists as embodied to be certain that his existence as thinking is distinct from his existence as embodied. While they do occur together as a matter of fact, they need not.

Note that when Descartes’ argument for the potential separate existence of his mind and body is understood in this way, it is easy to identify a further reason why Descartes is so determined, not just to distinguish between understanding and imagination, but positively to separate them out, such that he could exist as a thinking without having any capacity for thinking in the sense of imagining. For Descartes repeatedly makes clear that the faculty of imagination implicates body. By imagining, Descartes means the making of a mental picture and by this he means imagining a certain object to be causing a perceptual idea or experience of it in mind, which causal transaction he examines in order to note how the idea in his mind resembles the object responsible for the idea’s presence in his mind. Clearly, if this is what imagining is, it presupposes that he as the imaginer can be causally affected by external objects, in which case he must have body for them to act upon. Consequently, if Descartes is to be able to claim that he can exist as a thinking thing without having simultaneously to be a material thing, he must ensure that he possesses a faculty of or capacity for imagination merely contingently: while he has such a faculty or capacity as a matter of brute fact, his existence as thinking does not require him to have it. This is why it is so important to Descartes to ensure that imagination and understanding are different, indeed separable faculties or capacities.

§ 2: Descartes’ Interactionist Substance Dualism

But what exactly is Descartes asserting when he says that mind and body are potentially separate existents? Descartes explains what he means across pp.68-69:

… I perceive that the mind is not affected immediately by all the parts of the body but only by the brain or, perhaps, only by one small part of the brain, namely the part in which the common sense is said to be.⁸ Whenever this part is in the same state, it presents the same thing to the mind even though the other parts of the body may be in different states. This is proved by many experiences that need not be reviewed here.

I also perceive that the nature of the body is such that no part of it can be moved by another part at a certain distance from it, unless it can also be moved in the same way by any of the parts in between, even when the more remote part does nothing. For example, in a cord ABCD, if one end of it D is pulled, the other end A will be moved in the same may as if one of the intermediate parts, B or C, had been pulled and the end D had remained unmoved. In a similar way, when I feel a pain in the foot, physics teaches me that that sensation occurs by means of the nerves that are spread through the foot and are stretched from the foot to the brain like cords; when they are pulled in the foot, they also pull the inner parts of the brain where they terminate, and they stimulate a certain motion there, which was established by nature to affect the mind with a feeling of what seems like a pain in the foot. Since these nerves have to pass through the leg, the thigh, the loins, the back and the neck to reach from the foot to the brain, it can happen that, even if that section of the nerves which is in the foot is not affected but only some other intermediate section, evidently the very same motion occurs in the brain as when the foot is hurt, from which it will necessarily follow that the mind feels the same pain. The same thing must occur in the case of other sensations.

Finally, I perceive that any of the motions that occur in the part of the brain that affects the mind immediately trigger only one particular sensation in it; therefore the best arrangement that could be imagined here would be for it to trigger the specific sensation which, among all the sensations that it could possibly trigger, is conducive most often and to the greatest extent to the conservation of human health. Experience shows, however, that all the sensations with which we are endowed by nature are of this kind; therefore nothing can be found in them that does not bear witness to the power and goodness of God. Thus, for example, when the nerves in the foot are moved violently and more than usual, their motion, passing through the spinal cord to the inner parts of the brain, gives a signal to the mind to sense something, namely a pain that seems to be in the foot, by which it is stimulated to remove its cause, insofar as that is possible, as something harmful to the foot. Human nature could have been so constituted by God that the very same motion in the brain would make the mind aware of something else—for example, the motion itself as it occurs in the brain, in the foot, or in any of the intermediate places between the foot and brain, or of something completely different. But nothing else would have been as conducive to the conservation of the body. Likewise, when we need a drink, that gives rise to a certain dryness in the throat, which moves its nerves and, as a results the interior of the brain. This motion affects the mind with a sensation of thirsty, because there is nothing in this whole interaction that is more useful for us to know than that we need a drink for the conservation of our health, and likewise for other cases. (pp.68-69)

So the picture Descartes has of how his mind relates to his body is as follows: his mind stands in a particularly intimate relation to that part of his body which is his brain. This intimate relation is a causal one: events in the brain give rise, in one-to-one fashion, to events in the mind and vice versa. These causal interactions between the brain and the mind all pass presumably all pass through a special part of the brain which Descartes hypothesises to be the pineal gland—although it is important to note that nothing in Descartes’ general picture commits him to maintain that there is some such special part, much less that this is the pineal gland. (In other words, this latter part of the picture is a strictly empirical matter, to be decided by empirical investigation.)

Given this, the mind actually relates most intimately to the brain, and only indirectly to material entities beyond the brain, whether the body itself or even further removed material things, for example, the external objects of perceptual experience. For this reason, all it takes to ensure that the mind has a certain idea occur in it is that the causally corresponding neurophysiological event occur in the brain. Since this neurophysiological event could in principle be caused by all sorts of different things, it need not be caused by that entity which constitutes the ‘object’, i.e., the intentional reality or content of the idea in the mind. For any set of ideas {I₁, I₂, I₃, …} in the mind there are thus infinitely or at least indefinitely many causes of these ideas {C₁, C₂, C₃, …}. Naturally, to the set of possible causes there will belong the set {O₁, O₂, O₃, …}, which is the set of objects represented in the content of the ideas I₁, I₂, I₃, … . But this is not the only possible set of causes of these ideas. Here we already see why Descartes has assumed in his argument from dreaming and from the possibility of radical deception by an evil spirit that whether he is or is not dreaming, is or is not deceived by the evil spirit, he can still have the very same ideas in his mind. I will come back to this because, as we shall soon see, Descartes explicitly acknowledges this point.

§ 3: Problems for Substance Dualism⁹

Descartes calls the intimate relation between his mind and brain their substantial union, i.e., the union of these two radically different substances—radically different in that each of them has a different distinguishing attribute: non-spatially extended thinking in the case of the mind and spatially extended materiality in the case of the brain. The fact that the mind is not spatially extended suggests that, strictly speaking, the mind is not itself at any place in the universe; it does not, strictly speaking, have a spatial location. This points to the first problem for his doctrine of the substantial union of mind and body, or rather, mind and brain: how can something which lacks any spatial location exist in substantial union with something which does have a spatial location? Substantial union appears to be some kind of relation between two distinct entities. But surely the only distinct entities the brain can stand in any kind of relation to are ones which also possess a spatial location. This intimates that Descartes’ substance dualism flouts the intuition that entities in empirical reality are subject to principles of closure. Thus, we feel that if A exists in a certain spatio-temporal continuum and A stands in some relation R to something B, then B also exists in this spatiotemporal continuum.

Of particular importance is the principle of causal closure: if A is physical or natural, i.e., occurs as an entity in the physical or natural order, and A is either the cause or the effect of something B, then B is similarly physical or natural. Why do we insist on this kind of thing, particularly in the case of causality? The principle of causal closure in effect says that if two things stand in any causal relation to one another, then there is some fundamental respect in which they are alike: they are both physical or natural (in whatever sense one wants to give to the words ‘physical’ or ‘natural’). And the reason why we want there to be some such sameness is that this sameness captures the idea of there being some regularity or lawfulness in the interaction between things of A’s kind and things of B’s kind. The idea of causal closure captures the idea that the causal relation between A and B is the expression of some general regularity or law which applies across at least in some other cases, at some other places, when the circumstances are sufficiently similar. In short, the idea lying behind causal closure is that as a rule things of A’s kind will act upon, or be acted upon by, things of B’s kind in such and such ways under such and such conditions and not under other conditions.

It is clear that Descartes’ doctrine of substantial union offends against this. The reason why it offends against the principle of causal closure is twofold: on the one hand, Descartes construes mind and brain as radically distinct entities, that is, entities of two radically distinct kinds—precisely two distinct substances. On the other hand, he wants to allow, as is only plausible, a two-way causal interaction between the mind and the brain, hence between the mind and the body and ultimately the mind and the wider natural world. Because Descartes wants to allow causal relations between mind and brain, he really needs to ensure conformity of these relations to the principle of causal closure. But because he wants to insist on the first point, i.e., that mind and brain are two completely different substance, such that there is no level (except the completely abstract, empty level of their both being entities, etc.) at which they are the same kind of thing, he cannot secure causal closure. It is fundamentally this lack of causal closure, and thus the complete inability to characterise the interaction between mind and brain as a lawful one, which makes substantial union so mysterious. In particular, mind and brain are so different from one another that one can see no reason why the mind should be restricted to act and be acted upon through the body. If my mind is as distinct from my brain and body as Descartes maintains, why should I be restricted only to act on entities which are close to me rather than a long way off? Perhaps Descartes would answer by appeal to his physics, and in particular, that material entities only interact with one another if they are in direct contact with one another. So something A can only act upon something B a long way off from it by acting on things lying between A and B—see what Descartes says on p.68. But this will not do because the mind is precisely not a material thing; why can it not be ‘in touch’ will all things at all times and places?

I regard this as the most serious, indeed the only true difficulty in Descartes’ dualism metaphysics of mind, brain, body and thus nature—a difficulty which arises between his dualism is both a substance and an interactionist one. Others have, however, argued that there are even more problems with it. In particular, some have argued¹⁰ that the very idea of the mind exerting a causal influence on the brain is incoherent because it amounts to asserting that every so often the mind can so to speak suspend the laws of nature. Surely, to suggest that the mind acts autonomously upon the brain is to imply that it so to speak breaks the causal bonds between natural events, in this case, neurophysiological ones. But this is to suggest that there can be exceptions to the exceptionless laws which govern such events—evidently, a clear contradiction in terms.

It is not hard to see that this argument is question-begging. When Descartes says that the mind can act independently upon the brain, he is allowing precisely that events in brain are not subject to exceptionless law in any sense which would, for quite trivial reasons, preclude something’s intervening in the causal order of neural events. In other words, Descartes’ dualism entails that the laws governing the causal order in the brain, and thus in the body and the wider world, are not exceptionless in the sense presupposed by the objection. By presupposing that they are exceptionless in this total, mind-excluding sense, the objection is just begging the question against Descartes and dualism.

Another argument advanced against Descartes’ and indeed other forms of dualism is that it must contradict fundamental laws of science, in particular, laws of conservation. The Second Law of Thermodynamics states, at least in its Einsteinian version, the total quantity of matter and energy in the universe remain constant. Surely, if the mind can intervene into nature, changes must be wrought in the universe which increase or decrease the total quantity of matter plus energy, which contradicts this fundamental law of physics.

It is not hard to see that Descartes would not have been impressed by this objection. For he himself formulates in his Principles of Philosophy precisely his own version of this law. Naturally, the quantity which Descartes regards as remaining the same through the history of the universe is not matter plus energy. Indeed, it is not even matter, which was held to be what remained constant in quantity from around Newton’s time until Einstein. According to Descartes what is conserved is motion:¹¹ in the Principles of Philosophy, Part II, § 36, p.57, Descartes claims that God is the primary cause of motion and that He always maintains an equal quantity of it in the universe. Descartes would hardly have claimed this had he thought that his dualism commits him to denying it.

Indeed, it seems that Descartes knew of this kind of objection and the answer he gave to it is basically a version of the one C. D. Broad gave and I will give. Let the total sum or quantity at a certain point in time t of whatever you like—motion, matter, energy-plus-matter, or even, as is apparently said today, information—be the amount C. How many ways at some later time t + n can the universe be ordered while preserving this same quantity C? The answer is obviously infinitely many. All sorts of possible future arrangements of items in the world are consistent with preserving this same quantity C. Of course, given the actual state of the universe at t and the laws governing the universe all sorts of future arrangements will be ruled out. But this does not stop infinitely many being ruled in. So the mind has an infinite number of possibilities between which it can freely choose without contradicting any principle of conservation.

In general, it seems clear enough that this kind of argument can be extended to cover any law of natural science one cares to take. In other words, all the dualist has to do is to show that no set of laws formulated in purely in the terms, concepts and categories of natural science, whether quantitative or not, can rule the possibility out of there being infinitely many non-natural scientifically characterised states of the universe at time t + n which are consistent with this set of laws, given the natural scientific state of the universe at time t. The set of natural scientific laws limit reality in the way in which bisection limits a line: although this operation divides the line into two distinct intervals, and however one recursively applies the operation to the previous product of it, one is always left with an interval containing infinitely many elements. So, too, the set of natural scientific laws: however rich and numerous they get, the dualist has only to show that they never constrain one to just one non-natural scientific description of the future.

© Carleton B. Christensen, 2008, 2010, 2011, 2012, 2013 and 2014