Descartes: metaphysics and the philosophy of mind

Descartes: metaphysics and the philosophy of mind John Cottingham THE CARTESIAN PROJECT Descartes is rightly regarded as one of the inaugurators of the modern age, and there is no doubt that his thought profoundly altered the course of Western philosophy. In no area has this influence been more pervasive than in metaphysics and the philosophy of mind. But Descartes himself would perhaps have been surprised to learn that these aspects of his work were to be singled out by subsequent generations for special attention. For his own conception of philosophy, and of the philosophical enterprise he was engaged on, was enormously wide ranging; so far from being confined to ‘philosophy’ in the modern academic sense of that term, it had to do principally with what we should now call ‘science’. Descartes attempted, in his writings on cosmology, astronomy and physics, to develop a general theory of the origins and structure of the universe and the nature of matter, and he also did a considerable amount of detailed work in more specialized areas such as optics, meteorology, physiology, anatomy and medicine. In all these fields, Descartes aimed for explanatory economy; his goal was to derive all his results from a small number of principles of great simplicity and clarity, and he took mathematics as a model for the precise and unified structure of knowledge which he was seeking. Descartes’s ambition, however, was not just to produce a clear, precise and unified system of scientific explanations. He insisted that nothing could count as genuine scientia, as true knowledge, if it contained any hidden assumptions or presuppositions which had not been thoroughly scrutinized. As a schoolboy, he received a thorough training in philosophy and theology from the Jesuits at the College of La Flèche, but he later observed wryly that although the school had the reputation of being ‘one of the best in Europe’ he found that the philosophy he was taught, ‘despite being cultivated for many centuries by the most excellent minds’, contained not a single point that was not ‘disputed and hence doubtful’.¹ Although Descartes clearly believed that the scientific work he pursued as a young man was free from this son of uncertainty,² there remained the possibility that some unexamined premise—some ‘preconceived opinion’³—was infecting the whole system. Complete certainty could be attained only by ‘demolishing everything completely and starting again right from the foundations’.⁴ It is this ‘foundational’ project that forms the core of Cartesian metaphysics. In addition to his celebrated architectural metaphor of demolishing and rebuilding, Descartes also made use of an organic simile to explain the importance of metaphysics: ‘The whole of philosophy is like a tree: the roots are metaphysics, the trunk is physics and the branches emerging from the trunk are all the other sciences.’⁵ The simile is sometimes interpreted to mean that metaphysics is, for Descartes, the most important part of philosophy; but this is in some respects misleading. Descartes himself goes on to observe that ‘it is not the roots or the trunk of a tree from which one gathers fruit, but only the branches’, and he evidently saw the principal goal of his system as that of yielding practical benefits for mankind: in place of the ‘speculative philosophy taught in the schools’ he aimed to develop a ‘practical philosophy’ which would be ‘useful in life’ and ultimately make us ‘lords and masters of nature’.⁶ Metaphysics was in this sense a means to an end, for Descartes, rather than an end in itself; he had no patience with abstract speculation for its own sake, and frequently told questioners and correspondents not to become bogged down in metaphysical inquiries.⁷ Nevertheless, Descartes believed that at least once in a lifetime (semel in vita)⁸ anyone pretending to construct a reliable system of knowledge would have to engage in metaphysical inquiries: without such inquiries, there could be no guarantee of the stability of the rest of the system. Indeed (and the tree simile is again illuminating here), Descartes regarded the whole of human knowledge as a quasi-organic unity: in place of the scholastic conception of knowledge (ultimately derived from Aristotle) as an amalgam of separate disciplines, each with its own standards of precision and methods of inquiry, Descartes (reverting to an older Platonic idea) saw all truths as essentially interconnected. We need to grasp, he wrote in an early notebook, that all the sciences are ‘linked together’ like a series of numbers;⁹ later he developed the idea further: ‘those long chains of very simple and easy reasonings which geometers customarily use to arrive at their most difficult demonstrations gave me occasion to suppose that all the items which fall within the scope of human knowledge are interconnected in the same way.’¹⁰ Cartesian metaphysics attempts to start from scratch and establish, once and for all, the philosophical basis for these interconnections, aiming thereby to provide a kind of validation for the system as a whole. THE SIMPLE NATURES From some standard accounts of Descartes’s life one might get the impression that as a young man he was predominantly concerned with mathematical and scientific issues, and that his metaphysical interests came later. It is certainly true that mathematics was a major preoccupation of the young Descartes. Many of the results later incorporated in his Geometry11 were worked out during the 1610s, and we know from his letters that a great inspiration during his early years was the Dutch mathematician Isaac Beeckman, whom he met in Holland in 1618. Beeckman seems to have played for Descartes something of the role which Hume was later to play for Kant—waking him from his dogmatic slumbers: ‘you alone roused me from my state of indolence’ wrote Descartes to Beeckman on 23 April 1619 ‘and reawakened the learning that by then had almost disappeared from my mind’.¹² One of the chief points to strike Descartes was that mathematics could attain complete clarity and precision in its arguments, and that the demonstrations it employed were completely certain: no room was allowed for merely probabilistic reasoning.¹³ The mathematical model continued to influence his scientific work throughout the following decade,¹⁴ leading up to the composition of his treatise on physics and cosmology, Le Monde, which announced, at any rate in outline, a comprehensive programme for the elimination of qualitative descriptions from science in favour of exact quantitative analysis.¹⁵ Even in this early period, however, Descartes’s interests were never purely scientific (in the restricted modern sense): right from the start he seems to have been concerned with how the results achieved in mathematics and physics were to be related to more fundamental issues about the nature and basis of human knowledge. In his Regulae ad directionem ingenii (‘Rules for the Direction of our Native Intelligence’, written in Latin in the late 1620s but not published during his lifetime), Descartes makes it clear that his interest in subjects like geometry and arithmetic derives in large part from the fact that they are merely examples of a more general procedure of potentially universal application: I came to see that the exclusive concern of mathematics is with questions of order or measure, and that it is irrelevant whether the measure in question involves numbers, shapes, stars, sounds or any other object whatever. This made me realize that there must be a general science which explains all the points that can be raised concerning order and measure, irrespective of the subject-matter, and that this science deserves to be called mathesis universalis.¹⁶ It is important to note that the ‘universal discipline’ described here does not merely encompass quantitative subject matter. Descartes believes that there is a formal structure which all valid systems of knowledge manifest, and that this structure consists essentially in a hierarchical ordering: the objects of knowledge are to be arranged in such a way that we can concentrate to begin with on the items which are ‘simplest and easiest to know’, only afterwards proceeding to the more complex truths which are derived from these basic starting-points.¹⁷ The human intellect, Descartes goes on to explain, has the power to ‘intuit’ these ‘simple natures’ or fundamental starting-points for human knowledge: it simply ‘sees’ them with a simple and direct mental perception which allows for no possibility of error, since the simple natures are ‘all self-evident and never contain any falsity’.¹⁸ Some of the simple natures are ‘purely material’; these include shape extension and motion (and will be the building-blocks of Cartesian quantitative science). But others, Descartes asserts, are ‘purely intellectual’, and are ‘recognized by the intellect by a sort of natural light, without the aid of any corporeal image’; it is the intellectual simple natures which enable us, for example, to recognize ‘what knowledge or doubt or ignorance is’.¹⁹ Further, in addition to the intellectual simple natures, there are what Descartes calls the ‘common’ simple natures, which include the fundamental laws of logic (principles ‘whose self-evidence is the basis for all the rational inferences we make’).²⁰ Using the basic rules of inference, we can make necessary connections and so link the simple natures together to build up a body of reliable conclusions. Descartes, though in the Regulae he goes into no details of how such reasonings are conducted, provides some striking examples: ‘if Socrates says that he doubts everything, it necessarily follows that he understands at least that he is doubting’; or again, ‘I understand, therefore I have a mind distinct from a body’; or again (most striking of all), ‘sum, ergo Deus est’—‘I am, therefore God exists’.²¹ These examples have an unmistakable resonance for anyone familiar with Descartes’s mature metaphysics. The mind’s awareness of its own activity and of its incorporeal nature, and the route from knowledge of self to knowledge of God, were to be the central themes of Descartes’s metaphysical masterpiece— the Meditations on First Philosophy (1641). But already in the Regulae we find a recognition that these issues are an inescapable part of any well-ordered system of knowledge. The intellectual simple natures, together with the corporeal simple natures, comprise the two fundamental sets of building-blocks for human knowledge (and, to preserve the metaphor, the common simple natures, or logical rules of inference, are the cement which binds them together in the appropriate relations). ‘The whole of human knowledge’, Descartes resoundingly declares in Rule 12, ‘consists uniquely in our achieving a distinct perception of how all these simple natures contribute to the composition of other things’.²² The materials, then, are ready to hand, Descartes seems to be telling us in his early writings. The task of putting them together, of constructing a reliable edifice of knowledge, remains to be undertaken. But it is already clear that this will have to involve not just our mathematical intuitions about number and measure, but our introspective reflections on our own nature as conscious beings. Descartes claimed in his intellectual autobiography in the Discourse on the Method (1637) that the task was one whose importance he realized in his early twenties. Although he postponed its implementation, he knew that sooner or later a metaphysical journey of self-scrutiny would have to be undertaken: je pris un jour résolution d'étudier aussi en moi-même—‘I resolved one day to pursue my studies within myself’.²³ FIRST PHILOSOPHY In using the term ‘first philosophy’ to describe his fundamental metaphysical inquiries Descartes meant to draw attention to the fact that he proposed to deal ‘not just with questions about God and the soul but in general with all the first things to be discovered by philosophizing in an orderly manner’.²⁴ The discovery of reliable first principles is effected by a characteristic technique which has come to be known as the ‘method of doubt’. Descartes (though he was accused of being one25) is certainly no sceptic; he uses doubt purely as a means to an end, to demolish unreliable ‘preconceived opinions’ and clear away the resulting rubble in order to establish a bedrock of certainty. The strategy is sketched out in Part Four of the Discourse on the Method, and developed fully in the First Meditation; its point is neatly summarized in the Synopsis which Descartes had printed with the first edition of the Meditations: Reasons are provided which give us possible grounds for doubt about all things, especially material things, so long as we have no foundations for the sciences other than those which we have had up till now. Although the usefulness of such extensive doubt is not apparent at first sight, its greatest benefit lies in freeing us from all our preconceived opinions, and providing the easiest route by which the mind may be led away from the senses. The eventual result of this doubt is to make it impossible for us to have any further doubts about what we subsequently discover to be true.²⁶ Although commentators often present Descartes as a revolutionary philosopher, the technique of ‘leading the mind away from the senses’ had a long ancestry. Augustine had compared the senses to a ship bobbing around on the ocean; to achieve reliable knowledge (e.g. of mathematics), we have to leave the ship and learn to walk on dry land.²⁷ The general theme goes back ultimately to Plato, who insisted that the first step to true philosophical understanding is to move away from the shifting world of sense-based beliefs.²⁸ Descartes begins his metaphysics, then, with a traditional softening-up process. Drawing on classical arguments for doubt (whose revival had been a major feature of renaissance philosophy29), he undermines our confidence in the senses as a source of knowledge by pointing out that they sometimes deceive, and ‘it is prudent never to trust wholly those who have deceived us even once’.³⁰ He goes on to deploy the celebrated ‘dreaming argument’ (‘there are no sure signs by means of which being awake can be distinguished from being asleep’) to cast a general doubt on the reliability of the inference from sensory experiences to the existence of their supposed external causes. In the first phase of this argument, particular judgements like ‘I am sitting by the fire’ are impugned: any particular experience may be a dream. In the second, more radical, phase, doubt is cast on whole classes of objects: perhaps things like ‘heads, eyes and hands’ are all imaginary— part of some pervasive dream.³¹ The conclusion reached is that any science (such as physics) whose truth depends on the actual existence of objects is potentially doubtful; and that we may rely with certainty only on subjects like arithmetic and geometry, which deal ‘with the simplest and most general things, regardless of whether they exist in nature or not’.³² At this stage in the First Meditation Descartes launches into a far more disturbing and extreme doubt, which takes us into the heart of his metaphysics— the possibility of error even concerning the simplest and apparently most selfevident truths of mathematics. This possibility is initially introduced by invoking an idea which was much misunderstood by Descartes’s contemporaries, that of divine deception. Some found the suggestion impious; others saw the thrust of the argument as leading to atheism.³³ But in fact the project of the First Meditation, which is essentially one of suspension of belief, does not permit any assumptions to be made, one way or another, about the existence of God. Instead, we are presented with a simple dilemma: if there is an all-powerful creator, then he could ‘bring it about that I go wrong every time I add two and three or count the sides of a square’; if, on the other hand, there is no God, then I owe my existence not to a divine creator but to chance, or some other chain of imperfect causes, and in this case there is even less reason to believe that my intuitions about mathematics are reliable.³⁴ What the argument appears to do, in effect, is to cast doubt on the most basic perceptions of our intellect —on what Descartes had earlier, in the Regulae, called our intuition of the ‘simple natures’. But if the basic building-blocks of our knowledge are called into question, if the very framework of human cognition is suspect, then how could any cognitive process conceivably be validated? Descartes’s strategy in dealing with the dilemma he has raised is to show that even the most extreme doubt is self-defeating. ‘I immediately noticed’, he writes in the Discourse, ‘that while I was trying in this way to think everything false, it was necessary that I, who was thinking this, was something’.³⁵ In the Meditations, essentially the same point is made, but in a rather more vivid way: having dramatized the extreme level of doubt by deliberately imagining a ‘malicious demon of the utmost power and cunning who employs all his energies in order to deceive me’, Descartes triumphantly exclaims: In that case I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So… I must finally conclude that this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind.³⁶ Elsewhere expressed in the famous dictum Cogito ergo sum (‘I am thinking, therefore I exist’), this is the ‘Archimedean point’—the first indubitable certainty which the meditator encounters; it is, says Descartes, ‘so firm and sure that all the most extravagant suppositions of the sceptics are incapable of shaking it’, and hence he can ‘accept it without scruple as the first principle of the philosophy [he is] seeking’.³⁷ The precise logical status of Descartes’s cogito argument has called forth an unending stream of commentary and analysis. But Descartes himself regarded it as an extremely simple piece of reasoning: ‘when someone says I am thinking, therefore I exist, he does not have to deduce existence from thought by means of any syllogism, but recognizes it as something self-evident, by a simple intuition of the mind.’³⁸ There is, of course, nothing necessary about either one’s thought or one’s existence: I might not have existed; I could cease to think, or to exist, at any time. But what is necessary is that while I am actually engaged in thinking, I must exist. The validity of the cogito is thus not to be analysed simply in terms of the static inference patterns of formal logic; rather, it is something to be grasped by each individual meditator as he follows the Cartesian path and becomes aware of the unavoidable fact of his own existence as a subject of conscious awareness.³⁹ What is more, the fact of my thinking is self-confirming, in a way which is not the case with the other simple and self-evident truths (such as ‘two plus three makes five’) which Descartes has hitherto been considering. For the very act of doubting that I am thinking entails that I am thinking (since doubt is a species of thought).⁴⁰ In this sense, the cogito has a privileged status; it enjoys a primacy in the Cartesian quest for knowledge, since it alone is validated by the very fact of being doubted. There is, however, another, philosophically more problematic, aspect to the ‘primacy’ of the cogito. Descartes frequently described it as the ‘first principle’ of his philosophy; but astute contemporary critics challenged him on just this point. In order even to get as far as realizing his own existence, does not the meditator already have to have a considerable amount of knowledge—for example of what is meant by the very terms ‘thought’ and ‘existence’.⁴¹ In reply, Descartes conceded, and indeed insisted, that such prior conceptual knowledge was indeed required; the cogito was ‘primary’ only in the sense that it is the first existential truth which the meditator arrives at.⁴² But this reply in turn raises two fascinating difficulties. The first may be termed the problem of ‘Cartesian privacy’, and is one whose full implications have only become apparent in the twentieth century, chiefly as a result of the work of Ludwig Wittgenstein. What Wittgenstein showed, in his famous ‘private language argument’ was that for a term in any language to have meaning, there must be public criteria determining its correct application.⁴³ Yet this result, if we apply it to the Cartesian meditator, seems to undermine his entire project. For the project requires the meditator to doubt the existence of everything and everyone apart from himself, in order to reach subjective awareness of his own existence. Yet if the very understanding of terms like ‘thought’ and ‘existence’ presupposes a public realm of criteria determining their application, there is something inherently unstable about the private, autocentric perspective of the Cartesian quest for knowledge. If, as the Wittgensteinian argument seems to show, our grasp of concepts is an inescapably public, socially mediated, phenomenon, then the very ability of the meditator to employ concepts presupposes from the outset the existence of that extra-mental world which he is supposed to be doubting. From a modern perspective, in short, the very idea of the primacy of the subjective dissolves away, and yields to the primacy of the social. The second problematic feature about the primacy of the cogito arises even within the seventeenth-century context. Descartes’s concession that the cogito is not entirely self-standing, but presupposes the meditator’s grasp of the concepts involved, allows the following question to be raised. The extreme doubts of the First Meditation left open the possibility that the meditator might go astray ‘every time he adds two and three or counts the sides of a square, or in some even simpler matter, if that is imaginable’.⁴⁴ But if a deceiving God could pervert my intuitions regarding the simplest concepts of mathematics, why could he not also pervert my grasp of the fundamental concepts I need in order to reach the cogito? How, in short, can I trust my basic intuitions of the ‘intellectual simple natures’ like the concepts of thought and of doubt, not to mention the ‘common simple natures’, which include the concept of existence and also the fundamental rules of logic which seem necessary for any thought process at all to get off the ground? The correct answer to this conundrum, at least as far as Descartes’s own strategy is concerned, seems to be that the doubts of the First Meditation are not intended to be as radical as is often supposed. Doubts about our grasp of mathematics are raised by the deceiving God argument, but a careful reading of the First Meditation confirms that doubts about our intuitions of the intellectual simple natures are never entertained. Despite his talk of ‘demolishing everything’, Descartes is chiefly concerned, as he says in the Synopsis,⁴⁵ to challenge our preconceived opinions concerning the nature and existence of the material world around us. He wants to direct the mind away from physical things, so that it can turn in upon itself and let the ‘natural light’ within each of us reveal the truths that cannot be doubted. The Cartesian project is not to ‘validate reason’,⁴⁶ for such a project would be doomed to incoherence by the very attempt to undertake it by using the tools of reason. Descartes cannot, and does not propose to, generate a system of knowledge ex nihilo. What he does propose to do is to demolish commonly accepted foundations for knowledge, based largely on sensory experience and preconceived opinion, and utilize instead more stable foundations derived from the inner resources which have been implanted in each soul. The project is aptly summarized in Descartes’s dramatic dialogue, the Search for Truth, which was perhaps composed around the same time as the Meditations: I shall bring to light the true riches of our souls, opening up to each of us the means whereby we can find within ourselves, without any help from anyone else, all the knowledge we may need…in order to acquire the most abstruse items of knowledge that human reason is capable of possessing.⁴⁷ THE ROLE OF GOD It is scarcely possible to underestimate the role played by God in the development of Descartes’s foundational project. The meditator’s awareness of his own existence is a curiously transitory insight: I can be sure I exist only so long as I am thinking.⁴⁸ Admittedly, my awareness of myself as a thinking thing is quite indubitable and transparent: it surely could not turn out, Descartes observes, that ‘something I perceived with such clarity and distinctness was false’; and yet the earlier suggestion that an all-powerful God might make me go wrong ‘even in those matters which I think I see utterly clearly with the mind’s eye’ gives me pause for doubt. Although I have found one unshakeable truth, no general progress towards a systematic structure of knowledge will be possible unless I remove this residual doubt and establish ‘whether God exists and, if so, whether he can be a deceiver’.⁴⁹ Deprived, at this stage of his inquiries, of any certain knowledge of the outside world, the Cartesian meditator has to establish the existence of God drawing purely on the resources of his own consciousness. This is done by making an inventory of the ideas found within the mind. We cannot know at this stage whether our ideas correspond to anything real, but it is clear that they are ‘like images of things’: that is, they have a certain representational content.⁵⁰ Descartes now reasons that the content of each idea must have a cause; for nothing can come from nothing, yet ‘if we suppose that an idea contains something which was not in its cause, it must have got this from nothing’. In most cases, the content of an idea presents no great explanatory problem: the content of many of my ideas, observes Descartes, could easily have been drawn from my own nature; other ideas (like those of unicorns) are simply fictitious, or made up—put together by my own imagination. But the idea that gives me my understanding of ‘a supreme God, eternal, infinite, immutable, omniscient, omnipotent and the creator of all things’ is different: ‘all these attributes are such that the more carefully I concentrate on them, the less possible it seems that they could have originated from me alone.’ So the idea of God must have, as its cause, a real being who truly possesses the attributes in question. In creating me, God must have ‘placed this idea within me to be, as it were, the mark of the craftsman stamped on the work’.⁵¹ Of the many problematic features of this argument, the most striking is the extent to which it relies on what are (to the modern ear at least) highly questionable assumptions about causation. A swift reading might suggest that all Descartes needs is the (relatively uncontroversial) deterministic principle that everything has a cause (which Descartes expresses as the maxim that ‘Nothing comes from nothing’). But in fact the argument requires much more than this: it is not just that my idea of God needs a cause, but that its cause must actually contain all the perfection represented in the idea. It is ‘manifest by the natural light’ claims Descartes, that ‘there must be at least as much reality in the cause as in the effect’, and hence ‘that what is more perfect cannot arise from what is less perfect’.⁵² What Descartes is in effect presupposing here is a theory of causation that is deeply indebted to the scholastic philosophical apparatus which it is his official aim to supplant. According to the scholastic conception, causality is generally understood in terms of some kind of property transmission: causes pass on or transmit properties to effects, which are then said to derive their features from the causes.⁵³ And this in turn presupposes that certain kinds of similarity relations hold between causes and effects—in the words of the traditional maxim which Descartes is reported to have quoted approvingly, ‘the effect is like the cause’.⁵⁴ This allegiance to traditional models of causality casts a shadow on Descartes’s bold professions of novelty—his claim to be ‘starting afresh’ in metaphysics. That might not matter in itself, had not the explicit goal of the whole enterprise been to build on solid foundations by demolishing unscrutinized preconceptions. Yet to read through the proof of God’s existence in the Third Meditation is to be confronted with a positive barrage of traditional technical terms (‘substance’ and ‘mode’, and terms denoting various grades of reality—‘formal’, ‘objective’, ‘eminent’ and the like), whose application the reader is asked to take as self-evident. The scrupulous caution and methodological rigour which were employed earlier to establish the cogito argument seem to dissolve away here. In short, when endeavouring to establish the metaphysical foundations for his new science, Descartes seems unable to free himself from the explanatory framework of his scholastic predecessors.⁵⁵ But even if the details of Descartes’s proofs of God are taken on trust, deeper structural problems remain. The most serious is what has come to be known as the problem of the ‘Cartesian circle’ which was first raised by Descartes’s own contemporaries, notably Marin Mersenne and Antoine Arnauld.⁵⁶ The function of Descartes’s proof of God is supposed to be to establish the possibility of systematic knowledge. If a perfect God exists, then the intellectual apparatus which he bestowed on me cannot be intrinsically inaccurate. Of course, I may make mistakes from time to time, but this is due (Descartes argues in the Fourth Meditation) to incorrect use of free will: I often rashly jump in and give my assent to a proposition when I do not have a clear and distinct perception of it. But if I confine myself to what I clearly and distinctly perceive, I can be sure of avoiding error: ‘I shall unquestionably reach the truth if only I give sufficient attention to all the things which I perfectly understand, and separate these from all the cases where my apprehension is more confused and obscure’.⁵⁷ Provided I keep to this rule, I can achieve knowledge of countless things, including, most importantly, the structure of the physical universe—the ‘whole of that corporeal nature which is the subject of pure mathematics’.⁵⁸ Now the problem, in a nutshell, is this: if existence of a non-deceiving God has to be established in order for me to have confidence in the clear and distinct perceptions of my intellect, then how, without circularity, can I rely on the intellectual perceptions needed to construct the proof of God’s existence in the first place? Descartes’s answer to this challenge appears to be that the divine guarantee enables us to construct long chains of scientific reasoning but is not needed to establish the premises needed to prove God exists, since it is impossible to doubt these so long as we are actually attending to them.⁵⁹ Unfortunately, however, the premises of Descartes’s proofs for God seem to rely (suggested above) on a host of complex presuppositions which have to be taken on trust: the transparent, self-confirming quality which Descartes relied on to reach awareness of his own existence is simply not available in the elaborate causal reasoning needed to establish the existence of a perfect non-deceiving God. If this is right, then Descartes’s metaphysical project must be counted a failure: the journey from indubitable subjective self-awareness to systematic objective knowledge cannot be completed. The challenge which Descartes puts into the mouth of an imaginary objector in his dialogue The Search for Truth seems both apt and unanswerable: You seem to me to be like an acrobat who always lands on his feet, so constantly do you go back to your ‘first principle’. But if you go on in this way, your progress will be slow and limited. How are we always to find truths such that we can be as firmly convinced of them as we are of our own existence?⁶⁰ THE ETERNAL VERITIES The central place of God in Cartesian metaphysics should by now be more than clear. But no account of this relationship would be complete without some attention to one of Descartes’s most perplexing doctrines —that of the divine creation of the eternal truths. This is a doctrine which does not emerge explicitly in the Meditations, but it surfaces in the Replies to the Objections, and Descartes appears to have held it consistently throughout his life. He is reported to have insisted on it in an interview held two years before his death,⁶¹ and he explicitly asserted it, in his correspondence, as early as 1630: The mathematical truths which you call eternal have been laid down by God and depend on him no less than the rest of his creatures…. They are all inborn in our minds just as a king would imprint his laws on the hearts of all his subjects if he had enough power to do so.⁶² Traditional theology maintained that divine omnipotence does not entail the power to do absolutely anything, if ‘anything’ is taken to include even what is logically impossible. God cannot, on pain of absurdity, do what is selfcontradictory (e.g. make something which is both three-sided and a square); his supreme power operates, as it were, only within the sphere of the logically possible.⁶³ One might suppose that it is hardly an objectionable limitation on the power of God that he cannot do nonsensical and incoherent things like creating three-sided squares; but Descartes’s conception of the deity is of a being of absolutely infinite power—a being who is immune to any limitation which the human mind can conceive. Thus, not only is he the creator of all actually existing things, but he is the author of necessity and possibility; he was ‘just as free to make it not true that the radii of a circle were equal as he was free not to create the world’.⁶⁴ Some of Descartes’s critics objected that this was incoherent, but Descartes replied that just because we humans cannot grasp something is no reason to conclude that it is beyond the power of God. God thus turns out, on Descartes’s conception, to be in a real sense incomprehensible: our soul, being finite, cannot fully grasp (French, comprendre; Latin comprehendere) or conceive him.⁶⁵ From Descartes’s insistence on the ‘incomprehensibility’ of God, two profoundly disturbing problems arise for Cartesian philosophy. The first relates to Descartes’s attempt to found his scientific system on secure metaphysical foundations. In the First Meditation, the possibility had been raised that the human intellect might go astray ‘even in those matters which it seemed to perceive most evidently’. And the doubt so generated extended, on Descartes’s own insistence, even to our fundamental intuitions about the mathematical simple natures. But what of the intellectual simple natures—the fundamental conceptual apparatus needed for the meditator to arrive at knowledge of his own existence? We suggested earlier that if the doubt was allowed to go this far, then the very possibility of the meditator’s achieving any coherent reflection on his own existence as a conscious being would be foreclosed at the outset. But the doctrine of the divine creation of the eternal verities seems to entail that even our grasp of these basic concepts could be unreliable, in the sense that what is necessary for us may not be necessary for God. A gap is thus opened up between the basic processes of the human mind, and the true nature of things. And if we have no reliable hold on the true logical implications of our concepts, if there is no sure route from what is ‘true for us’ to what is ‘true for God’, the entire Cartesian journey from indubitable subjective awareness to reliable objective knowledge seems threatened at the outset. From this nightmare of opacity, an even more disturbing threat to the Cartesian project seems to follow. If the structure of the fundamental principles of logic is not ultimately accessible to human reason, but depends on the inscrutable will of God, then the very notion of ultimate truth, of something’s being ‘true for God’, turns out to be beyond our grasp.⁶⁶ In his programme for science, Descartes needs to insist constantly on the immutability and coherence of the fundamental laws which govern the universe. By appealing to these laws, we are able, asserts Descartes, to derive a whole structure of necessary connections which operate in the world, and unravel a complex series of results which describe the behaviour of matter in motion in accordance with the laws of mathematics.⁶⁷ But now, given that the rationale behind these necessities is ultimately opaque to us, it seems to follow that the rationally ordered universe which Cartesian science had hoped to reveal becomes in the end merely a series of arbitrary divine fiats; and against this background it is hard to see how the laws of nature could ultimately be construed as anything more than brute regularities. In short, the doctrine of the divine creation of the eternal truths generates, from our perspective at least, an ineradicable element of contingency in the system. The project of Cartesian rationalism, of uncovering a universe whose structure is supposed to be in principle transparent to the human intellect, now seems radically unstable. At the heart of the system is a worm of doubt, an element of arbitrariness which prefigures, if only faintly and in outline, the post-Humean world in which the working of the universe is in the end opaque to human reason.⁶⁸ SCIENCE AND THE HUMAN MIND The problems touched on in the previous sections have to do with the role of God in Descartes’s conception of knowledge, and the status of scientific truth in the Cartesian system. But there are certain features of the Cartesian programme which remain largely unaffected by these foundational issues. Whatever the metaphysical status of the ultimate laws governing the universe, Descartes could, and did, claim that his scientific approach was, in explanatory terms, both economical and comprehensive. These two features of Cartesian science are in fact two sides of the same coin. The system could claim to be economical because it subsumed a wide variety of phenomena under a very few simple principles specifying the behaviour of matter in motion;⁶⁹ and it could claim to be comprehensive because it included hitherto separated categories of events— terrestrial and celestial, organic and inorganic, natural and artificial—under a single explanatory apparatus.⁷⁰ In his early work, Le Monde, Descartes aimed to describe the evolution of a complete universe, starting from a chaotic initial configuration of matter in motion and using simple mechanical principles to explain the subsequent formation of stars and planets, the Earth and the Moon, light and heat, the ebb and flow of the tides, and much else besides. And he explicitly went on to include the human body as something which could be explained mechanically on the self-same principles. The fact that living creatures are ‘automata’—that is, initiate their own movements without requiring any external impulse—was, Descartes claimed, no obstacle whatever to his explanatory programme: We see clocks, artificial fountains, mills and other such machines, which, although only man-made, have the power to move of their own accord in many different ways. But I am supposing this machine [of the human body] to be made by the hand of God, and so I think you may reasonably believe it capable of a greater variety of movements than I could possibly imagine in it, and of exhibiting a greater mastery than I could possibly ascribe to it.⁷¹ Descartes’s investigations into animal physiology (he performed frequent experimental dissections during his long residence in Holland72) led him to the conclusion that many of the workings of the body could be explained by reference to the minute particles of matter which he called ‘animal spirits’, transmitted to and from the brain via the nervous system. Such ‘animal spirits’ were purely physical in character, operating in a way very analogous to that in which gases or fluids are transmitted along systems of pipes and conduits. There was no need to posit any internal principle such as a ‘nutritive’ or ‘sensitive’ soul in order to explain biological processes like digestion and growth; indeed, the ordinary laws of matter in motion were quite sufficient to account even for complex animal behaviour like pursuit and flight.⁷³ The ways in which the beasts operate can be explained by means of mechanics, without invoking any ‘sensation, life or soul’;⁷⁴ and even in the case of humans, we have no more reason to believe that it is our soul which produces the movements which we know by experience are not controlled by our will than we have reason to think that there is a soul in a clock which makes it tell the time.⁷⁵ Reflection led Descartes to conclude, however, that there were severe limits on the power of mechanical explanations when it came to accounting for the characteristically human processes of thought and language. In the Discourse, he argues that one could in principle construct an artificial automaton which was indistinguishable from a dog or a monkey. But any such attempt to mimic human capacities would be doomed to failure. A mechanical android, however complex, would betray its purely physical origins in two crucial respects: first, it could never possess genuine language, and second, it could never respond intelligently to the manifold contingencies of life in the way in which humans do. The first of these arguments, the argument from language, is a crucial weapon in Descartes’s strategy of showing that human capacities are not just different in degree from those of non-human animals, but are radically different in kind: We can certainly conceive of a machine so constructed that it utters words, and even utters words which correspond to bodily actions causing a change in its organs (e.g. if you touch it in one spot it asks what you want of it, and if you touch it in another it cries out that you are hurting it, and so on). But it is not conceivable that such a machine should produce different arrangements of words so as to give an appropriately meaningful answer to whatever is said in its presence, as even the dullest of men can do.⁷⁶ The vital point here is that a mechanical system produces responses in accordance with a fixed schedule: there is a finite number of possible responses, each triggered by a specified stimulus. But genuine language is ‘stimulus-free’: it involves the ability to respond innovatively to an indefinite range of situations.⁷⁷ Hence it is ‘for all practical purposes impossible for a machine to have enough different organs to make it act in all the contingencies of life in the way in which our reason makes us act’.⁷⁸ The power of reason in human beings was thus, Descartes concluded, incapable of being explained by reference to the workings of a mechanical system; a material structure, however complex its organization, could never approach the human capacity for thought and language. And hence, even in his earliest scientific work, Descartes acknowledged a limit in principle to the scope of physical explanation. The properties of stars and planets, rainbows and vapours, minerals, plants and animals could all be reduced to complex interactions of matter in motion. But if God wanted to create a thinking human being, he would have to create, in addition to all the physiological mechanisms of the brain and nervous system, a separate entity, a ‘rational soul’.⁷⁹ The nature of this soul, and its relation to the physical world, was to become one of Descartes’s principal preoccupations, when he came to develop his mature metaphysics. THE INCORPOREALITY THESIS The Discourse on the Method contains, in outline, Descartes’s central doctrines on the nature of the human soul. The central claim, which he introduces at the end of a summary of his previous work on physiology, is that ‘the rational soul, unlike any other things previously dealt with, cannot be derived in any way from the potentiality of matter, but must be specially created’.⁸⁰ Anti-reductionism about the human mind—the insistence that the phenomena of cognition and rationality are not reducible to physical events—is a thesis that still finds a good deal of support among present-day philosophers. But nowadays this thesis is generally advanced as a thesis about mental properties or events: statements about such properties or events, asserts the anti-reductionist, cannot be replaced without remainder by statements about purely physical properties or events (e.g. statements about brain workings). But many modern anti-reductionists are still in some sense physicalists; that is, they hold that mental processes and events must be realized or instantiated in the workings of physical systems, so that, if all such systems were destroyed, no mental happenings could occur. Descartes, however, takes a far more radical line. The Cartesian view is that the distinction between mind and matter is a matter of ontology: the mind is a distinct entity in its own right, which operates, or can in principle operate, entirely independently of the material universe. This is the claim which has come to be known as Cartesian (or substantival) dualism: the mind is ‘really distinct’ from the body, a separate and independent substance. Descartes’s initial argument for the incorporeality of the mind or soul (he makes no distinction between the two terms81) arises from the meditative process which leads to the cogito. In becoming aware of his own existence, the meditator is able to separate or bracket off all his beliefs about the existence of an external material world: Next I examined attentively what I was. I saw that while I could pretend that I had no body, and that there was no world and no place for me to be in, I could not for all that pretend that I did not exist…. From this I knew I was a substance whose whole essence or nature is solely to think, and which does not require any place, or depend on any material thing, in order to exist. Accordingly this ‘I’, that is the soul by which I am what I am, [ce Moi, c’est à dire l’Ame par laquelle je suis ce que je suis] is entirely distinct from the body…and would not fail to be whatever it is even if the body did not exist.⁸² It could be (and indeed was in Descartes’s own day83) objected that merely because I can think of ‘myself’ without thinking of my body, it does not follow that I could really exist if my body were destroyed. After all, I may (if I am ignorant of the real nature of gold) be able to think of gold without thinking of its atomic structure, but it does not follow that something could still exist as gold without that structure. Descartes’s position, however, is that if an object (in this case the thinking thing that is ‘me’) can be clearly conceived of as lacking a given property (in this case having a body), then that property cannot be essential to the object in question. The phrase ‘whose whole essence or nature is solely to think’ is the key to Descartes’s reasoning here. Drawing on the traditional terminology of substance and attribute, Descartes maintains that each substance has a nature or essence— that is, a property or set of properties which makes it what it is. The standard scholastic view (derived from Aristotle) held that there is a large plurality of substances, but Descartes reduces created substances to just two categories: mind and matter. The principal attribute of matter is extension (the possession of length, breadth and height), and all the features of matter are reducible to ‘modes’ or modifications of this essential characteristic; thus a piece of wax, for example, may take on a variety of shapes, but all these are simply mathematically determinable modifications of res extensa, or ‘extended substance’.⁸⁴ But now, just as all the properties of physical things are modifications of extension, so all the properties of a mind (thinking, willing, doubting, desiring and so on) are all modifications of res cogitans or thinking substance. And Descartes took it as self-evident that the properties of thought and extension were not just different but utterly distinct and incompatible. ‘On the one hand,’ he later wrote in the Sixth Meditation, I have a clear and distinct perception 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 body, in so far as this is simply an extended, non-thinking thing. And accordingly it is certain that I [that is the soul by which I am what I am] is really distinct from the body and can exist without it.⁸⁵ By the time this full-blown argument is deployed in the Sixth Meditation, Descartes has more resources at his disposal than he had in the Discourse when he blandly observed that he could pretend he did not have a body without thereby pretending that the ‘I by which I am what I am’ did not exist. In the Sixth Meditation, God (whose existence is taken to have been proved at this stage) is invoked as the guarantor of the clear and distinct perceptions of the human mind. Hence, if we can clearly and distinctly conceive of X without Y, it follows that Y cannot be essential to X. The modern reader may feel uncomfortable here: surely all the argument proves is that mind and body could conceivably exist separately, not that they are in fact separate entities. But it is precisely the conceivability of mind separate from body which Descartes relies on in order to establish his dualistic thesis: ‘the mere 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.’⁸⁶ Whether in fact the mind will exist after the death of the body is something that Descartes is content to leave undetermined by reason: it is a matter of religious faith.⁸⁷ It is enough that it is, as we should say nowadays, logically possible that it should exist without physical matter. That possibility, which Descartes takes himself to have demonstrated, is enough to guarantee the incorporeality thesis—that what makes me me, the conscious awareness of myself as a res cogitans, cannot depend on the existence of any physical object. What the above analysis suggests is that Descartes’s version of dualism stands or falls with the claim that the existence of mind without matter is at least a logical possibility. And a good many modern philosophers, however adamantly they may be disposed to insist that mental properties are structural or functional properties of a physical or biological system (the brain, the nervous system), often concede that disembodied consciousness is at least logically conceivable. But what does the alleged logical possibility of mind without matter amount to? It must presumably boil down to some such claim as that there is no logical contradiction in conjoining (as Descartes does in the Discourse) the two statements (a) ‘I exist as a conscious being at time t’ and (b) ‘my body (including my brain and nervous system) does not exist at time t’. But this seems a very weak argument. As Leibniz was later to observe (in a rather different context), it is not enough, to establish the coherence of a set of propositions, that one cannot immediately detect any obvious inconsistency in them. For it is quite possible that a set of propositions which seems consistent on the face of it might turn out on further analysis to contain hitherto undetected incoherence.⁸⁸ Borrowing the terminology of Karl Popper from our own time (and transferring it from the realm of philosophy of science to that of logic), we may say that claims of logical possibility are falsifiable (by producing a contradiction) but not conclusively verifiable. Now admittedly, when we are dealing with very simple and transparent truths (those of elementary arithmetic or geometry, for example), we may be entitled to be sure that there could be no hidden inconsistency which would undermine the logical coherence of a group of propositions. But when we are dealing with a phenomenon as complex and difficult as consciousness, it seems far from clear that we are entitled to declare, just by simple reflection, that its occurrence in the absence of any physical substrate is a coherent possibility. Moreover, when we start to ponder on many of the key elements that make up our conscious life—‘internal’ sensations of pain and pleasure, and ‘external’ sensations such as those of vision, touch, hearing, taste and smell—then it becomes difficult to see how, if at all, these could be attributed to a disembodied entity.⁸⁹ Such sensory events do not of course exhaust our conscious experience: there remain what Descartes called the ‘pure’ cogitations of the intellect —thoughts about triangles or numbers, for example. But it is by no means clear that such ‘pure’ forms of abstract thought would be enough to constitute an individual conscious existence.⁹⁰ In short, the logical possibility of the continued independent existence of the Moi—the ‘soul by which I am what I am’—is by no means as clear and straightforward a matter as Descartes invites us to suppose. THE RELATION BETWEEN MIND AND BODY Despite his insistence on the incorporeality of the mind, Descartes both acknowledged, and made serious attempts to explain, the intimate relationship between mind and body. That relationship, as he frequently pointed out, is manifested in the facts of everyday experience: nature teaches me by these sensations of pain, hunger, thirst and so on, that I am not merely present in my body as a sailor is present in a ship, but that I am very closely conjoined and as it were intermingled with it, so that I and the body form a unit.⁹¹ Contemporaries of Descartes were puzzled by this admission: during an interview which he conducted with the philosopher in the Spring of 1648, the young Dutchman Frans Burman asked him how the soul could be affected by the body, and vice versa, given the supposed radical difference in their natures. Descartes answered that the point was ‘difficult to explain’, but that our own inner experience was ‘so clear’ that it could not be gainsaid.⁹² Reflections on the phenomenology of sensory experience help to identify what Descartes is pointing to here. When we are thirsty, to take one of his examples, we do not merely have an intellectual understanding that our body needs water; we experience a characteristic and intrusive sensation of a distinctive kind—the mouth and the throat ‘feel dry’. What kind of event is this ‘feeling’? According to the standard expositions of ‘dualism’ found in modern textbooks on the philosophy of mind, to have a sensation like thirst is to be in a certain kind of conscious state; and hence, feeling thirsty is, for the dualist, assignable to the category of mind rather than body, since all consciousness belongs on the ‘mental’ side of the dualist’s mind-body divide. So familiar has this approach to the phenomena of ‘consciousness’ become that it takes some effort to realize that Descartes’s own views about sensory experience are in fact rather different. Descartes does not say that sensations are mental events simpliciter; on the contrary, he explicitly says that ‘I could clearly and distinctly understand the complete “me” without the faculty of sensation’.⁹³ Sensation, though it is an inescapable part of my daily experience, does not form an essential part of the res cogitans that is ‘me’. Rather, Descartes explains, it is a ‘confused’ mode of awareness which ‘arises from the union and as it were intermingling of the mind with the body’.⁹⁴ It emerges from this that Descartes’s universe is not quite as neat and tidy as the label ‘Cartesian dualism’ tends to suggest. It is true that there exist, for Descartes, examples of pure thinking things—angels are his standard example— whose existence consists essentially and entirely in modifications of intellection and volition; such beings are examples of a res cogitans in the strict sense. On the other side of the divide, there is pure res extensa, mere extended matter whose every feature can be analysed as some kind of modification of the geometrically defined properties of size and shape;⁹⁵ the human body is an example of a structure, or assemblage of structures, composed entirely of extended matter. But human beings fit into neither of the two categories so far described. For a human being consists of a mind or soul ‘united’ or ‘intermingled’ with a body; and when such intermingling occurs, there ‘arise’ further events, such as sensations, which could not be found in minds alone or in bodies alone. Although the ‘union’ between body and soul is explicitly mentioned in the Meditations, the concept is left somewhat obscure, and it was not until he was questioned in detail by Princess Elizabeth of Bohemia that Descartes came to examine in more detail exactly what it implied. We have, he wrote in a letter to the Princess of 21 May 1643, various ‘primitive notions’ which are ‘models on which all our other knowledge is patterned’. He proceeds to list some of the categories which he had much earlier labelled as ‘simple natures’: first, there are ‘common’ notions, such as being, number and duration, ‘which apply to everything we can conceive’; second, there is the corporeal notion of extension, ‘which entails the notions of shape and motion’; and third, there is the ‘notion of thought, which includes the conceptions of the intellect and the inclinations of the will’. All this is straightforward Cartesian doctrine. But now Descartes adds a fourth category: ‘as regards soul and body together, we have the notion of their union, on which depends our notion of the soul’s power to move the body, and the body’s power to act on the soul and cause sensations and passions’.⁹⁶ He later made it clear that the notion of a ‘union’ was meant to be taken literally: to conceive the union between two things is to conceive them as one single thing…. Everyone invariably experiences the union within himself without philosophizing. Everyone feels that he is a single person [une seule personne] with thought and body so related by nature that the thought can move the body and feel the things that happen to it.⁹⁷ The notion that two different substances can unite to form a single thing is not, in itself, obscure or problematic. We are familiar nowadays, for example, with the idea that hydrogen and oxygen can unite to form water; furthermore, this ‘substantial union’ generates ‘emergent’ properties—water has properties such as that of being drinkable which were not present in its constituent elements— and this (though it is not of course Descartes’s own example) might be thought to give some grip on the Cartesian notion that events like sensations emerge or ‘arise’ when mind and body are united, even though they are not part of the essence of either res cogitans or res extensa. Nevertheless, Descartes himself clearly felt that his notion of the ‘substantial union’ of mind and body presented problems. For mind and body, as defined throughout his writings, are not just different, but utterly incompatible substances: in terms of their essential characteristics, they mutually exclude one another, since mind is defined as nonextended and indivisible, whereas matter is by its nature extended and divisible. And it is not easy to see how incompatible items can be, in any intelligible sense, ‘united’. As Descartes rather ruefully put it: it does not seem to me that the human mind is capable of conceiving at the same time the distinction and the union between body and soul, because for this it is necessary to conceive them as a single thing and at the same time to conceive them as two things, and this is absurd.⁹⁸ CAUSAL INTERACTION AND OCCASIONALISM The idea of the union of utterly heterogeneous items is not the only problematic feature of Descartes’s theory of the mind and its relation to the body. Descartes frequently talks in a way which suggests both that the mind has causal powers vis-à-vis the body (e.g. it can cause the body to move), and that the body has causal powers with respect to the soul (e.g. passions and feelings are ‘excited’ by corporeal events in the blood and nervous system). A great deal of Descartes’s last work, the Passions of the Soul, is devoted to examining the workings of this two-way causal flow between body and mind. The following is his account of memory: When the soul wants to remember something, this volition makes the [pineal] gland lean first to one side and then to another, thus driving the animal spirits [the tiny, fast moving particles which travel through the nervous system] towards different regions of the brain until they come upon the one containing traces left by the object we want to remember. These traces consist simply in the fact that the pores of the brain through which the spirits previously made their way owing to the presence of this object have thereby become more apt than the others to be opened in the same way when the spirits again flow towards them. The spirits thus enter these pores more easily when they come upon them, thereby producing in the gland that special movement which represents the same object to the soul, and makes it recognize the object as the one it wanted to remember.⁹⁹ What strikes the reader here is not so much the wealth of obsolete physiological detail (modern readers will readily be able to substitute electrochemical events in the cerebral cortex for Descartes’s movements of the pineal gland and ‘animal spirits’) as the way in which that physiological detail is expected to ‘mesh’ with events in the non-physical realm of the soul. Descartes has managed to supply a host of mechanisms whereby movements, once initiated in the pineal gland, can be transferred to other parts of the brain and body; but he does not seem to have tackled the central issue of how an incorporeal soul can initiate such movements in the first place. And the same problem will apply when the causal flow is in the other direction. Descartes devotes a lot of attention to the physiological mechanisms whereby bodily stimuli of various kinds cause changes in the nervous system and brain which ‘dispose’ the soul to feel emotions like anger or fear.¹⁰⁰ But he does not explain how mere brain events, however complex their physiological genesis, could have the power to arouse or excite events in the mental realm. Why exactly is the causal aspect of the mind-body relation problematic for Descartes? The answer, in brief, is that throughout the rest of his metaphysics and physics he seems to presuppose that causal transactions should be in some sense transparent to the human intellect. ‘The effect is like the cause’ was a standard maxim of the scholastics which (as noted earlier in this chapter) Descartes readily accepts.¹⁰¹ In his causal proofs of God’s existence he relies on the principle that the cause of an object possessing a given degree of perfection must itself possess as much or more perfection: whatever is found in the effect must be present in the cause. In physics, too, Descartes often seems inclined to require explanations that reveal transparent connections between causes and effects (in the unfolding of the laws of motion, for example, a simple transmission model is invoked—a cause transmits or passes on a determinate quantity of motion to its effect).¹⁰² In all these cases, Descartes apparently wants to be able to appeal to something very simple and self-evident: if we could not ‘see’ how effects inherited features from their causes, we would have a case of something arising ‘from nothing’, which would be absurd. But now it is immediately clear that no such transparency could be available in the mindbody interactions which Descartes describes in such detail in the Passions of the Soul. Transparent connections can be unfolded so long as we remain within the realm of physiology and trace how the stimulation of a sense organ generates changes in the ‘animal spirits’ which in turn cause modifications in the movements of the pineal gland. But at the end of the story, there will be a mental event which simply ‘arises’ in the soul: the smooth progression of causal explanations abruptly jolts to a halt. Whatever it is that bridges the gulf between the bodily and the mental realms, it seems that it must remain opaque to causal explanation, in the sense in which that notion is normally understood by Descartes.¹⁰³ Descartes’s way round this impasse is to invoke an innate, divinely ordained, power of the human mind. In creating the human soul, God structured it in such a way that various sensory experiences will ‘arise’ in it whenever the body to which it is united is stimulated in a certain way. Thus, the mind has the innate capacity of ‘representing colours to itself on the occasion of certain corporeal motions [in the brain]’. There is, in effect, no genuine causal transmission between mind and body; ‘nothing reaches the mind from external objects except corporeal motions’; we make judgements about external things ‘not because these things transmit ideas to our mind through the sense organs, but because they transmit something which, at exactly the right moment, gives the mind the occasion to form these ideas by means of the faculty innate to it.’¹⁰⁴ What we have here is something powerfully reminiscent of developments later in the seventeenth century—the occasionalism of Malebranche, and the Leibnizian theory of ‘pre-established harmony’. And the lesson to be learned from this is that the ideas of Malebranche and Leibniz were not, as is sometimes suggested, bizarre attempts to cobble together an ad hoc solution to the problem of mindbody interaction which Descartes had bequeathed to Western philosophy; rather, they take their cue from Descartes’s own terminology, and his insistence that the relationship between physical events and mental phenomena must be explained on the model of divinely decreed correlations rather than transparent causal transactions. The heterogeneous worlds of mind and matter cannot, properly speaking, interact; only the decrees of God can ensure that they work harmoniously together. To conclude from this that Descartes’s theory of the mind is a failure would be easy enough; but any sense of superiority that the modern commentator may feel should be tempered by the thought that, even today, the relationship between brain occurrences and conscious experience is very far from having been elucidated in a coherent and philosophically satisfying way. What may be a more fruitful theme for reflection is Descartes’s own implicit recognition of the limits of human knowledge. The Cartesian project for a unified system of knowledge, founded on transparently clear first principles, faltered, as we saw in the first half of this chapter, when the human mind came to confront the incomprehensible greatness of God. And in a different way, the project faltered when it came to integrating into science that most basic fact of human awareness—our everyday experience, through our external and internal senses, of the world around us and the condition of our bodies. To ‘explain’ that awareness, Descartes was constrained to admit that only the decrees of God, ultimately opaque to human reason, will suffice. Causal transparency gives way to mere regular conjunction. If this, once again, seems to prefigure the thought of Hume, that should perhaps be no surprise. For however much commentators may wish to present it as a contest between opposing teams of ‘rationalists’ and ‘empiricists’, the history of the early modern period is a continuous unfolding tapestry in which the threads endlessly cross and re-cross. The picture that has come down to us is the work of many hands, but however we view it, there can be no disputing Descartes’s role as one of its principal designers. NOTES 1 AT VI 8: CSM I 115. ‘AT’ refers, by volume and page number, to the standard Franco-Latin edition of Descartes: Oeuvres de Descartes, ed. C.Adam and P. Tannery [6.1]. ‘CSM’ refers by volume and page number to the standard English translation: The Philosophical Writings of Descartes, vols I and II, ed. J.Cottingham, R.Stoothoff and D.Murdoch, and ‘CSMK’ refers to vol. III (The Correspondence) by the same translators and A.Kenny [6.2]. ‘CB’ refers to Descartes’ Conversation with Burman, ed. and trans. J.Cottingham [6.5]. 2 Compare Descartes’s remarks on his early work, Le Monde, in Part Five of the Discourse (AT VI 41f.; CSM I 131). 3 For the significance of this term (Latin praejudicium), see Principles of Philosophy, Book I, arts 1 and 71. 4 First Meditation: AT VII 17; CSM II 12. 5 From the introduction to the 1647 French edition of the Principles of Philosophy (first published in Latin in 1644): AT VIIIA 14; CSM I 186. The simile is also found in other writers of the period, notably Francis Bacon (De augmente scientiarum, 3, i). 6 Discourse on the Method (1637), Part Six: AT VI 62; CSM I 142. 7 cf. Conversation with Burman (AT V 156; CB 30) and letter to Elizabeth of 28 June 1643 (AT III 695; CSMK 228). 8 First Meditation: AT VII 17; CSM II 12. 9 AT X 215; CSM I 3. 10 AT VI 19; CSM I 120. 11 First published in French in 1637 as one of the three ‘specimen essays’ (the other two were the Optics and the Meteorology) illustrating Descartes’s method. 12 AT X 163; CSMK 4. Descartes dedicated to Beeckman his first work, the Compendium Musicae, a study of the application of mathematical methods to the understanding of harmony and dissonance. 13 cf. Discourse, Part Two (AT VI 19; CSM I 120) and Part One (AT VI 8; CSM I 115). 14 Descartes began work on his Optics and Meteorology prior to 1630; cf. CSM I 109f. 15 See especially AT XI 26; CSM I 89. Descartes never published The World. Although it was complete and ready to go to press in 1633, he suppressed the work on hearing of the condemnation of Galileo by the Inquisition for advocating the heliocentric hypothesis. 16 Regulae, Rule 4: AT X 378; CSM I 19. 17 See the end of Rule 4: ‘I have resolved in my search for knowledge of things to adhere unswervingly to a definite order, always starting from the simplest and easiest things and never going beyond them till there seems to be nothing further to be achieved where they are concerned’ (AT X 379; CSM I 20). See also Rule 5, which insists on the importance of ‘ordering and arranging the objects on which we must concentrate our mind’s eye if we are to discover some truth’ (ibid.), and Rule 6, which asserts that the ‘main secret of the method is to distinguish the simplest things from those that are complicated’ (AT X 381; CSM I 21). 18 Rule 12: AT X 420; CSM I 45. 19 ibid. 20 AT X 419; CSM I 45. In addition, the common simple natures include fundamental concepts like ‘unity, existence and duration’ which may be applied either to the material or to the intellectual simple natures. 21 AT X 421; CSM I 46. 22 AT X 427; CSM I 49. 23 Discourse, Part One, AT VI 10; CSM I 116. Descartes implies that his resolution was made during his visit to Germany as a young man of 23, when he had his famous series of dreams in the ‘stove heated room’ near Ulm on the Danube. These early reflections are described in Part Two of the Discourse; see also the early notebooks (AT X 217; CSM I 4). In Discourse, Part Three, Descartes suggests that after postponing these metaphysical inquiries he took them up again soon after arriving in Holland (i.e. after 1629). We know from a letter to Mersenne that about this time he actually began to compose a ‘little treatise on metaphysics’ whose principal themes were ‘to prove the existence of God and that of our souls when they are separated from our bodies’: je ne dis pas que quelque jour je n’achevasse un petit traité de Métaphysique lequel j’ai commencé étant en Frise, et dont les principaux points sont de prouver l’existence de Dieu et celle de nos âmes, lorsqu’elles sont séparées du corps (23 November 1630, AT I 182; CSMK 29). 24 Discussing what title to give his écrit de métaphysique (what we now know as the Meditations), Descartes wrote: Je crois qu’on le pourra nommer… Meditationes de Prima Philosophia; car je n’y traité pas seulement de Dieu et de l’âme, mais en général de toutes les premières choses qu’on peut connaître en philosophant par ordre (letter to Mersenne of 11 November 1640, AT III 329; CSMK 158). The terms ‘metaphysics’ and ‘first philosophy’ were of course not invented by Descartes; the latter comes from Aristotle who used it to describe fundamental philosophical inquiries about substance and being, and the former from the name given by early editors to Aristotle’s treatise on ‘first philosophy’ (the name ‘metaphysics’ coming originally from the fact that in collected editions of Aristotle this work was traditionally placed after (Greek meta) his physics). Descartes’s conception of metaphysics was significantly different from the Aristotelian one, however, not least (as will appear) because of its radically subjective orientation. For a discussion of crucial disparities between Aristotelian essences and Cartesian simple natures, see J.-L.Marion, ‘Cartesian metaphysics and the role of the simple natures’, in J.Cottingham (ed.) Cambridge Companions: Descartes [6.32]. 25 In particular by the Jesuit Pierre Bourdin; cf. Seventh Replies, AT VII 549; CSM II 375. 26 AT VII 12; CSM II 9. 27 Soliloquies, Book I, ch. 4; cf. AT VII 205; CSM II 144. 28 cf. Republic, 525. The abstract reasoning of mathematics is, for Plato, as it was later to be for Augustine and Descartes, a paradigm of stable and reliable cognition of the kind which sense-based beliefs could never attain. The term ‘rationalism’ is an over-used and problematic one in the history of philosophy, but it can serve to indicate interesting similarities between groups of philosophers: one such indisputable similarity is the mistrust of the senses which runs like a clear thread from Plato down to Descartes (and beyond). For further discussion of the label ‘rationalist’, see J.Cottingham, The Rationalists [6.12], ch. 1. 29 Compare, for example, Francisco Sanches, Quod Nihil Scitur (1581), ed. and trans. E.Limbrick and D.F.S.Thomson (Cambridge, Cambridge University Press, 1988). See also R.Popkin, The History of Scepticism from Erasmus to Descartes [6.23]. 30 AT VII 18; CSM II 12. Elsewhere Descartes discusses such standard examples as that of the straight stick which looks bent in water: AT VII 438; CSM II 295. 31 AT VII 20; CSM II 14. The dreaming argument in fact has a number of complex twists and turns, but the two main phases, particular and general, are as indicated. The argument appears in much more compressed form in Descartes’s summary of his metaphysical views in Part Four of the Discourse: considérant que toutes les mêmes pensées que nous avons étant éveillés nous peuvent aussi venir quand nous dormons, sans qu’il y en ait aucune pour lorsqui soit vraie, je me résolus de feindre que toutes les choses qui m’étaient jamais entrées en l’esprit n’étaient non plus vraies que les illusions de mes songes. 32 ibid. 33 cf. AT VIIIB 175; CSMK 223. 34 For more on this argument, see R.Stoothoff, ‘Descartes’ dilemmatic argument’ [6. 52]. 35 AT VI 32; CSM I 127. 36 Haud dubio igitur sum, si me fallit; & fallat quantum potest, nunquam tamen efficiet, ut nihil sim quamdiu me aliquid esse cogitabo. Adeo ut…denique statuendum sit hoc pronuntiatum, Ego sum, ego existo quoties a me profertur, vel mente concipitur, necessario esse verum (AT VII 25; CSM II 17). 37 The phrasing here is from the Discourse, Part Four (AT VI 32; CSM I 127). The notion of the Archimedean point appears in the Second Meditation: ‘Archimedes used to demand just one firm and immovable point in order to shift the entire earth; so I too can hope for great things if I manage to find just one thing, however slight, that is certain and unshakeable’ (AT VII 24; CSM II 16). The actual phrase cogito ergo sum appears in the Principles of Philosophy, Part I, article 7; its French equivalent, je pense, donc je suis, in the Discourse, op. cit. 38 AT VII 140; CSM II 100. For discussion of the cogito argument, see A. Kenny, Descartes [6.20], ch. 3; B.Williams, Descartes [6.28], ch. 3; M.Wilson, Descartes [6.29], ch. 2. 39 Compare Descartes’s comment in the Preface to the Meditations: ‘I would not urge anyone to read this book except those who are able and willing to meditate seriously with me’ (AT VII 9; CSM II 8). For the importance of the meditator’s activity, see Wilson, op. cit., and compare J.Hintikka, ‘Cogito ergo sum: Inference or Performance?’ [6.46], reprinted in W.Doney, Descartes [6.33]. 40 For more on this, see J.Cottingham, Descartes [6.11], 38ff. 41 cf. Sixth Objections: AT VII 413; CSM II 278. 42 See Principles of Philosophy, Part I, art. 10 (AT VIIIA 8; CSM I 196). 43 See L.Wittgenstein, Philosophical Investigations, trans. G.E.M.Anscombe (Oxford, Blackwell, 1953), I, p. 243. 44 AT VII 21; CSM II 14. 45 In prima [Meditatione] causae exponuntur propter quas de rebus omnibus, prasertim materialibus, possumus dubitare (AT VII 13; CSM II 9). 46 cf. H.Frankfurt, Demons, Dreamers and Madmen. The Defence of Reason in Descartes’ Meditations [6.14]. 47 AT X 496; CSM II 400. For the work’s date of composition, see CSM II 399. 48 ‘I am, I exist—that is certain. But for how long? For as long as I am thinking…’ (AT VII 27; CSM II 18). 49 All quotations in this paragraph are from the opening of the Third Meditation: AT VII 35–6; CSM 24–5. 50 Or what Descartes calls (using scholastic terminology) ‘objective reality’ (realitas objectiva). The more helpful reference to the ‘representational’ aspect of ideas is supplied in the 1647 French translation of the Meditations (by the Duc de Luynes) which was issued with Descartes’s approval. 51 Third Meditation: AT VII 40, 45, 51; CSM II 28, 31, 35. 52 Lumine naturali manifestum est tantundem ad minimum esse debere in causa… quantum in ejusdem causae effectu…Hinc autem sequitur [non] posse…fieri…id quod magis perfectum est…ab eo quod minus (AT VII 40; CSM II 28). 53 It is interesting to note that Cartesian physics, in so far as it offers explanations purely in terms of mathematical covering laws, offers the possibility of dispensing with traditional models of causality; the opportunity, however, was not fully seized by Descartes (see pp. 222–5). For more on Descartes’s conception of causality, and its influence on the philosophical history of the seventeenth and eighteenth centuries, see N.Jolley, The Light of the Soul [6.19], ch. 3. 54 Conversation with Burman, AT V 156; CB 17. For more on the scholastic background to Descartes’s causal proof for God’s existence, see J.Cottingham, ‘A New Start? Cartesian Metaphysics and the Emergence of Modern Philosophy’, in T.Sorell (Ed.) The Rise of Modern Philosophy [6.37]. 55 In the Fifth Meditation, Descartes offers a further proof of God’s existence, namely that since God is defined as the supremely perfect being, all perfections, including that of existence, must necessarily be part of his essential nature: it is quite evident that existence can no more be separated from the essence of God than the fact that its three angles equal two right angles can be separated from the essence of a triangle, or than the idea of a mountain can be separated from the idea of a valley. Hence it is no less of a contradiction to think of God (that is a supremely perfect being) lacking existence (that is, lacking a perfection) than it is to think of a mountain without a valley. (AT VII 66; CSM II 46) A version of this argument (known since Kant as the ‘ontological argument’) had originally been put forward by St Anselm of Canterbury in the eleventh century, but it had been strongly criticized by Aquinas, and its revival by Descartes was a source of considerable surprise to his contemporaries. For some of the objections raised by contemporary critics, see the First Set of Objections to the Meditations, AT VII 98; CSM II 70. For a discussion of some of the problematic aspects of the argument, see further J.Cottingham, Descartes [6.11], 57ff. 56 Second and Fourth Objections respectively: AT VII 125; CSM II 89 and AT VII 214; CSM II 150. 57 AT VII 62; CSM II 43. 58 Fifth Meditation: AT VII 71; CSM II 49. 59 cf. Second Replies, AT VII 140ff.; CSM II 100ff.; Fourth Replies, AT VII 246; CSM II 171; Conversation with Burman, AT V 148; CB 6. For more on the circle objection and Descartes’s reply to it, see especially A.Gewirth, ‘The Cartesian Circle’ [6.45] and L.Loeb, ‘The Cartesian Circle’, in J.Cottingham (ed.) Cambridge Companions: Descartes [6.32]. 60 AT VII 526; CSM II 419. 61 Conversation with Burman (1648): AT V 160; CSMK 343. 62 Letter to Mersenne of 15 April 1630, AT I 145; CSMK 23; cf. Sixth Replies: ‘God did not will that the three angles of a triangle should be equal to two right angles because he recognized that it could not be otherwise;…it is because he wills that the three angles of a triangle should necessarily equal two right angles that this is true and cannot be otherwise’ (AT VII 432; CSM II 291). 63 See, for example, Aquinas, Summa Theologiae, Ia, 25, 3. See further A.Kenny, Descartes [6.20], 37f. 64 Letter to Mersenne of 27 May 1630; AT I 152; CSMK 25. 65 Notre âme, étant finie, ne le puisse comprendre ni concevoir (ibid.). For further discussion of this theme, cf. J.-M.Beyssade, ‘The Idea of God’ [6.38]. 66 For an interesting development of this point, see S.Gaukroger, Cartesian Logic [6. 15], ch. 2. 67 See Principles, Book II, art. 64. 68 I use the term ‘post-Humean’ in accordance with what may be called the traditional interpretation of Hume as a philosopher who undermined the idea of science as the discovery of necessary connections in the world. For an alternative interpretation, see J.Wright, The Sceptical Realism of David Hume (Cambridge, Cambridge University Press, 1983). 69 For the simplicity and economy claimed by Descartes for his system see the letter to Huygens of 10 October 1642 (AT II 797; CSMK 216) and Principles, Part IV, arts 199 and 206. 70 For the breaking down of the barriers between terrestrial and celestial, see Principles, Part IV, passim; for the barrier between organic and inorganic, see Description of the Human Body (AT XI 226; CSM I 315); for that between natural and artificial, see Treatise on Man (AT XI 120f., CSM I 99f.). 71 Treatise on Man: AT XI 120; CSM I 99. Though published (after Descartes’s death) as a separate work, the Treatise on Man was originally conceived by Descartes as part of Le Monde. See further CSM I 79. 72 He lived for a time in Kalverstraat in Amsterdam, where he obtained carcasses for dissection from the butcher; some of his later experiments in vivisection are described in the Description of the Human Body (AT XI 242f.; CSM I 317f.). 73 AT VII 230; CSM II 161. 74 AT VII 426; CSM I 288. 75 Description of the Human Body: AT XI 226; CSM I 315. 76 Discourse, Part Five, AT VI 56f.; CSM I 140. 77 This feature of language has been highlighted in our own day by Noam Chomsky: for his account of language as essentially ‘stimulus-free’, see N. Chomsky, Language and Mind (New York, Harcourt, Brace & World, 1968). 78 Discourse, Part Five, op. cit. For more on the strengths and weaknesses of Descartes’s language argument, see J.Cottingham, ‘Cartesian Dualism: Theology, Metaphysics and Science’, in Cambridge Companions: Descartes [6.32]. 79 In the Treatise on Man, Descartes compares the nervous system to the complex set of pipes and reservoirs found in a park with fountains and moving statues: Visitors who enter the grottos of these fountains…cannot enter without stepping on certain tiles which are so arranged that if, for example, they approach a Diana who is bathing they will cause her to hide in the reeds, and if they move forward to pursue her they will cause a Neptune to advance and threaten them with his trident. All these events happen purely mechanically, according to the ‘whim of the engineers who made the fountains’. But a human being is more than a physiological system of pipes and levers: when a rational soul is present in the machine, it will have its principal seat in the brain and reside there like the fountain keeper who must be stationed at the tanks to which the fountain’s pipes return if he wants to produce or prevent or change their movements in some way. (AT XI 131; CSMI 101) 80 Discourse, Part Five: AT VI 59; CSM I 141. 81 cf. Synopsis to Meditations: ‘…l’esprit OH l’âme de l’homme (ce que je ne distingue point)…’ (AT IX 11; CSM II 10). 82 Discourse, Part Four: AT VI 32f.; CSM I 127. 83 cf. AT VII 8; CSM II 7. 84 Meditation Two: AT VII 30–1; CSM II 20–1. 85 AT VII 78; CSM II 54. The gloss in square brackets does not appear in the original Latin text of 1641, but is inserted in the later French translation. See above, note 50. 86 Sixth Meditation, op. cit. 87 See AT VII 49; CSM II 33: ‘I do not take it upon myself to try to use the power of human reason to settle any of those matters which depend on the free will of God.’ 88 Compare Leibniz’s critique of the ontological argument: Discourse on Metaphysics, §23. See further J.Cottingham, The Rationalists [6.12], 100. 89 See further T.Penelhum, Survival and Disembodied Existence (London, Routledge, 1968). 90 This line of thought was the basis of the ‘Averroist heresy’ (condemned by the Lateran council in 1513) which denied personal immortality. See further AT VII 3; CSM II 4; and Cottingham, cited in note 78. 91 Sixth Meditation: AT VII 81; CSM II 56. 92 Conversation with Burman, AT V 163; CB 28. 93 Imagination and sensation are faculties ‘sine quibus totum me possum dare & distincte intelligere’ (AT VII 78; CSM II 54). The ‘hybrid’ faculties of sensation and imagination are often singled out for special treatment by Descartes. Compare a passage earlier in the same Meditation, which asserts that imagination is not a necessary constituent of my essence as a thinking thing: vim imaginandi, prout differt a vi intelligendi, ad mei ipsius, hoc est ad mentis meae essentiam non requiri (AT VII 73; CSM II 51). For more on the ‘hybrid’ faculties, see J.Cottingham, Descartes [6.11], I22ff. 94 Sixth Meditation: AT VII 81; CSM II 56. 95 To this should be added motion, which Descartes sometimes describes as a straightforward mode of extension (AT II 650; CSMK 217), but which, in the Principles, is said to be specially imparted to matter by divine action (see Principles, Part II, arts 36ff. 96 AT III 665; CSMK 218. 97 Letter of 28 June 1643, AT III 692 and 694; CSMK 227 and 228. 98 ibid. 99 Passions of the Soul, Part I, art. 42 (AT XI 360; CSM I 344). Descartes regarded the pineal gland (or conarion) as the ‘principal seat of the soul’ and the locus of psycho-physical interactions; cf. 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