History of philosophy

DESCARTES: METAPHYSICS AND THE PHILOSOPHY OF MIND

Descartes: metaphysics and the philosophy of mindJohn CottinghamTHE CARTESIAN PROJECTDescartes is rightly regarded as one of the inaugurators of the modern age, andthere is no doubt that his thought profoundly altered the course of Westernphilosophy. In no area has this influence been more pervasive than inmetaphysics and the philosophy of mind. But Descartes himself would perhapshave been surprised to learn that these aspects of his work were to be singled outby subsequent generations for special attention. For his own conception ofphilosophy, and of the philosophical enterprise he was engaged on, wasenormously wide ranging; so far from being confined to ‘philosophy’ in themodern academic sense of that term, it had to do principally with what we shouldnow call ‘science’. Descartes attempted, in his writings on cosmology,astronomy and physics, to develop a general theory of the origins and structureof the universe and the nature of matter, and he also did a considerable amountof detailed work in more specialized areas such as optics, meteorology,physiology, anatomy and medicine. In all these fields, Descartes aimed forexplanatory economy; his goal was to derive all his results from a small numberof principles of great simplicity and clarity, and he took mathematics as a modelfor the precise and unified structure of knowledge which he was seeking.Descartes’s ambition, however, was not just to produce a clear, precise andunified system of scientific explanations. He insisted that nothing could count asgenuinescientia,as true knowledge, if it contained any hidden assumptions orpresuppositions which had not been thoroughly scrutinized. As a schoolboy, hereceived a thorough training in philosophy and theology from the Jesuits at theCollege of La Flèche, but he later observed wryly that although the school hadthe reputation of being ‘one of the best in Europe’ he found that the philosophyhe was taught, ‘despite being cultivated for many centuries by the most excellentminds’, contained not a single point that was not ‘disputed and hence doubtful’.¹Although Descartes clearly believed that the scientific work he pursued as ayoung man was free from this son of uncertainty,²there remained the possibilitythat some unexamined premise—some ‘preconceived opinion’³—was infectingthe whole system.Complete certainty could be attained only by ‘demolishingeverything completely and starting again right from the foundations’.⁴It is this‘foundational’ project that forms the core of Cartesian metaphysics.In addition to his celebrated architectural metaphor of demolishing andrebuilding, Descartes also made use of an organic simile to explain theimportance of metaphysics: ‘The whole of philosophy is like a tree: the roots aremetaphysics, the trunk is physics and the branches emerging from the trunk areall the other sciences.’⁵The simile is sometimes interpreted to mean thatmetaphysics is, for Descartes, the most important part of philosophy; but this isin some respects misleading. Descartes himself goes on to observe that ‘it is notthe roots or the trunk of a tree from which one gathers fruit, but only thebranches’, and he evidently saw the principal goal of his system as that ofyielding practical benefits for mankind: in place of the ‘speculative philosophytaught in the schools’ he aimed to develop a ‘practical philosophy’ which wouldbe ‘useful in life’ and ultimately make us ‘lords and masters of nature’.⁶Metaphysics was in this sense a means to an end, for Descartes, rather than anend in itself; he had no patience with abstract speculation for its own sake, andfrequently told questioners and correspondents not to become bogged down inmetaphysical inquiries.⁷Nevertheless, Descartes believed that at least once in alifetime(semel in vita)⁸anyone pretending to construct a reliable system ofknowledge would have to engage in metaphysical inquiries: without suchinquiries, 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 thewhole of human knowledge as a quasi-organic unity: in place of the scholasticconception of knowledge (ultimately derived from Aristotle) as an amalgam ofseparate disciplines, each with its own standards of precision and methods ofinquiry, Descartes (reverting to an older Platonic idea) saw all truths asessentially interconnected. We need to grasp, he wrote in an early notebook, thatall the sciences are ‘linked together’ like a series of numbers;⁹later he developedthe idea further: ‘those long chains of very simple and easy reasonings whichgeometers customarily use to arrive at their most difficult demonstrations gave meoccasion to suppose that all the items which fall within the scope of humanknowledge are interconnected in the same way.’¹⁰Cartesian metaphysicsattempts to start from scratch and establish, once and for all, the philosophical basisfor these interconnections, aiming thereby to provide a kind of validation for thesystem as a whole.THE SIMPLE NATURESFrom some standard accounts of Descartes’s life one might get the impressionthat as a young man he was predominantly concerned with mathematical andscientific issues, and that his metaphysical interests came later. It is certainly truethat mathematics was a major preoccupation of the young Descartes. Many ofthe results later incorporated in hisGeometry11 were worked out during the1610s, and we know from his letters that a great inspiration during his earlyyears was the Dutch mathematician Isaac Beeckman, whom he met in Holland in1618. Beeckman seems to have played for Descartes something of the role whichHume was later to play for Kant—waking him from his dogmatic slumbers: ‘youalone roused me from my state of indolence’ wrote Descartes to Beeckman on 23April 1619 ‘and reawakened the learning that by then had almost disappearedfrom my mind’.¹²One of the chief points to strike Descartes was thatmathematics could attain complete clarity and precision in its arguments, andthat the demonstrations it employed were completely certain: no room wasallowed for merely probabilistic reasoning.¹³The mathematical model continuedto influence his scientific work throughout the following decade,¹⁴leading up tothe composition of his treatise on physics and cosmology,Le Monde,whichannounced, at any rate in outline, a comprehensive programme for theelimination of qualitative descriptions from science in favour of exactquantitative analysis.¹⁵Even in this early period, however, Descartes’s interests were neverpurelyscientific (in the restricted modern sense): right from the start he seems to havebeen concerned with how the results achieved in mathematics and physics wereto be related to more fundamental issues about the nature and basis of humanknowledge. In hisRegulae ad directionem ingenii(‘Rules for the Direction of ourNative Intelligence’, written in Latin in the late 1620s but not published duringhis lifetime), Descartes makes it clear that his interest in subjects like geometryand arithmetic derives in large part from the fact that they are merely examplesof a more general procedure of potentially universal application:I came to see that the exclusive concern of mathematics is with questions oforder or measure, and that it is irrelevant whether the measure in questioninvolves numbers, shapes, stars, sounds or any other object whatever. Thismade me realize that there must be a general science which explains all thepoints that can be raised concerning order and measure, irrespective of thesubject-matter, and that this science deserves to be calledmathesisuniversalis.¹⁶It is important to note that the ‘universal discipline’ described here does notmerely encompass quantitative subject matter. Descartes believes that there is aformal structure which all valid systems of knowledge manifest, and that thisstructure consists essentially in a hierarchical ordering: the objects of knowledgeare to be arranged in such a way that we can concentrate to begin with on theitems which are ‘simplest and easiest to know’, only afterwards proceeding tothe more complex truths which are derived from these basic starting-points.¹⁷The 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 nopossibility of error, since the simple natures are ‘all self-evident and nevercontain any falsity’.¹⁸Some of the simple natures are ‘purely material’; these include shapeextension and motion (and will be the building-blocks of Cartesian quantitativescience). But others, Descartes asserts, are ‘purely intellectual’, and are‘recognized by the intellect by a sort of natural light, without the aid of anycorporeal image’; it is the intellectual simple natures which enable us, forexample, to recognize ‘what knowledge or doubt or ignorance is’.¹⁹Further, inaddition 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 wemake’).²⁰Using the basic rules of inference, we can make necessary connectionsand so link the simple natures together to build up a body of reliable conclusions.Descartes, though in theRegulaehe goes into no details of how such reasoningsare conducted, provides some striking examples: ‘if Socrates says that he doubtseverything, it necessarily follows that he understands at least that he isdoubting’; 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 Godexists’.²¹These examples have an unmistakable resonance for anyone familiarwith Descartes’s mature metaphysics. The mind’s awareness of its own activityand of its incorporeal nature, and the route from knowledge of self to knowledgeof God, were to be the central themes of Descartes’s metaphysical masterpiece—theMeditations on First Philosophy(1641). But already in theRegulaewe find arecognition that these issues are an inescapable part of any well-ordered systemof knowledge. The intellectual simple natures, together with the corporeal simplenatures, comprise the two fundamental sets of building-blocks for humanknowledge (and, to preserve the metaphor, the common simple natures, orlogical rules of inference, are the cement which binds them together in theappropriate relations). ‘The whole of human knowledge’, Descartes resoundinglydeclares in Rule 12, ‘consists uniquely in our achieving a distinct perception ofhow all these simple natures contribute to the composition of other things’.²²Thematerials, then, are ready to hand, Descartes seems to be telling us in his earlywritings. The task of putting them together, of constructing a reliable edifice ofknowledge, remains to be undertaken. But it is already clear that this will have toinvolve not just our mathematical intuitions about number and measure, but ourintrospective reflections on our own nature as conscious beings. Descartesclaimed in his intellectual autobiography in theDiscourse 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 ametaphysical journey of self-scrutiny would have to be undertaken:je pris unjour résolution d'étudier aussi en moi-même—‘I resolved one day to pursue mystudies within myself’.²³FIRST PHILOSOPHYIn using the term ‘first philosophy’ to describe his fundamental metaphysicalinquiries 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 firstthings to be discovered by philosophizing in an orderly manner’.²⁴The discoveryof reliable first principles is effected by a characteristic technique which has cometo be known as the ‘method of doubt’. Descartes (though he was accused ofbeing one25) is certainly no sceptic; he uses doubt purely as a means to an end, todemolish unreliable ‘preconceived opinions’ and clear away the resulting rubblein order to establish a bedrock of certainty. The strategy is sketched out in PartFour of theDiscourse on the Method,and developed fully in the First Meditation;its point is neatly summarized in the Synopsis which Descartes had printed withthe first edition of theMeditations:Reasons are provided which give us possible grounds for doubt about allthings, especially material things, so long as we have no foundations forthe sciences other than those which we have had up till now. Although theusefulness of such extensive doubt is not apparent at first sight, its greatestbenefit lies in freeing us from all our preconceived opinions, and providingthe easiest route by which the mind may be led away from the senses. Theeventual result of this doubt is to make it impossible for us to have anyfurther doubts about what we subsequently discover to be true.²⁶Although 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; toachieve reliable knowledge (e.g. of mathematics), we have to leave the ship andlearn to walk on dry land.²⁷The general theme goes back ultimately to Plato,who insisted that the first step to true philosophical understanding is to moveaway from the shifting world of sense-based beliefs.²⁸Descartes begins hismetaphysics, then, with a traditional softening-up process. Drawing on classicalarguments for doubt (whose revival had been a major feature of renaissancephilosophy29), he undermines our confidence in the senses as a source ofknowledge by pointing out that they sometimes deceive, and ‘it is prudent neverto trust wholly those who have deceived us even once’.³⁰He goes on to deploythe celebrated ‘dreaming argument’ (‘there are no sure signs by means of whichbeing awake can be distinguished from being asleep’) to cast a general doubt onthe reliability of the inference from sensory experiences to the existence of theirsupposed external causes. In the first phase of this argument, particularjudgements like ‘I am sitting by the fire’ are impugned: any particular experiencemay be a dream. In the second, more radical, phase, doubt is cast on wholeclasses of objects: perhaps things like ‘heads, eyes and hands’ are all imaginary—part of some pervasive dream.³¹The conclusion reached is that any science (suchas physics) whose truth depends on the actual existence of objects is potentiallydoubtful; and that we may rely with certainty only on subjects like arithmetic andgeometry, which deal ‘with the simplest and most general things, regardless ofwhether they exist in nature or not’.³²At this stage in the First Meditation Descartes launches into a far moredisturbing and extreme doubt, which takes us into the heart of his metaphysics—the possibility of error even concerning the simplest and apparently most selfevidenttruths of mathematics. This possibility is initially introduced by invokingan idea which was much misunderstood by Descartes’s contemporaries, that ofdivine deception. Some found the suggestion impious; others saw the thrust ofthe argument as leading to atheism.³³But in fact the project of the FirstMeditation, which is essentially one of suspension of belief, does not permit anyassumptions 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-powerfulcreator, then he could ‘bring it about that I go wrong every time I add two andthree or count the sides of a square’; if, on the other hand, there is no God, then Iowe my existence not to a divine creator but to chance, or some other chain ofimperfect causes, and in this case there is even less reason to believe that myintuitions about mathematics are reliable.³⁴What the argument appears to do, ineffect, is to cast doubt on the most basic perceptions of our intellect —on whatDescartes had earlier, in theRegulae,called our intuition of the ‘simple natures’.But if the basic building-blocks of our knowledge are called into question, if thevery framework of human cognition is suspect, then how could any cognitiveprocess conceivably be validated?Descartes’s strategy in dealing with the dilemma he has raised is to show thateven the most extreme doubt is self-defeating. ‘I immediately noticed’, he writesin theDiscourse,‘that while I was trying in this way to think everything false, itwas necessary that I, who was thinking this, was something’.³⁵In theMeditations,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 energiesin order to deceive me’, Descartes triumphantly exclaims:In that case I too undoubtedly exist, if he is deceiving me; and let himdeceive me as much as he can, he will never bring it about that I amnothing so long as I think that I am something. So… I must finally concludethat this proposition,I am, I exist,is necessarily true whenever it is putforward by me or conceived in my mind.³⁶Elsewhere expressed in the famous dictumCogito ergo sum(‘I am thinking,therefore I exist’), this is the ‘Archimedean point’—the first indubitable certaintywhich the meditator encounters; it is, says Descartes, ‘so firm and sure that allthe most extravagant suppositions of the sceptics are incapable of shaking it’, andhence he can ‘accept it without scruple as the first principle of the philosophy [heis] seeking’.³⁷The precise logical status of Descartes’scogitoargument has called forth anunending stream of commentary and analysis. But Descartes himself regarded itas an extremely simple piece of reasoning: ‘when someone saysI am thinking,therefore I exist,he does not have to deduce existence from thought by means ofany syllogism, but recognizes it as something self-evident, by a simple intuitionof the mind.’³⁸There is, of course, nothing necessary about either one’s thoughtor one’s existence: I might not have existed; I could cease to think, or to exist, atany time. But what is necessary is that while I am actually engaged in thinking, Imust exist. The validity of thecogitois thus not to be analysed simply in termsof the static inference patterns of formal logic; rather, it is something to begrasped by each individual meditator as he follows the Cartesian path and becomesaware of the unavoidable fact of his own existence as a subject of consciousawareness.³⁹What is more, the fact of my thinking is self-confirming, in a waywhich is not the case with the other simple and self-evident truths (such as ‘twoplus three makes five’) which Descartes has hitherto been considering. For thevery act of doubting that I am thinking entails that I am thinking (since doubt is aspecies of thought).⁴⁰In this sense, thecogitohas a privileged status; it enjoys aprimacy in the Cartesian quest for knowledge, since it alone is validated by thevery fact of being doubted.There is, however, another, philosophically more problematic, aspect to the‘primacy’ of thecogito. Descartes frequently described it as the ‘first principle’of his philosophy; but astute contemporary critics challenged him on just thispoint. In order even to get as far as realizing his own existence, does not themeditator already have to have a considerable amount of knowledge—forexample of what is meant by the very terms ‘thought’ and ‘existence’.⁴¹In reply,Descartes conceded, and indeed insisted, that such prior conceptual knowledgewas indeed required; thecogitowas ‘primary’ only in the sense that it is the firstexistential truth which the meditator arrives at.⁴²But this reply in turn raises twofascinating difficulties. The first may be termed the problem of ‘Cartesianprivacy’, and is one whose full implications have only become apparent in thetwentieth century, chiefly as a result of the work of Ludwig Wittgenstein. WhatWittgenstein showed, in his famous ‘private language argument’ was that for aterm in any language to have meaning, there must be public criteria determiningits correct application.⁴³Yet this result, if we apply it to the Cartesian meditator,seems to undermine his entire project. For the project requires the meditator todoubt the existence of everything and everyone apart from himself, in order toreach subjective awareness of his own existence. Yet if the very understandingof terms like ‘thought’ and ‘existence’ presupposes a public realm of criteriadetermining their application, there is something inherently unstable about theprivate, autocentric perspective of the Cartesian quest for knowledge. If, as theWittgensteinian argument seems to show, our grasp of concepts is an inescapablypublic, socially mediated, phenomenon, then the very ability of the meditator toemploy concepts presupposes from the outset the existence of that extra-mentalworld 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 theprimacy of the social.The second problematic feature about the primacy of thecogitoarises evenwithin the seventeenth-century context. Descartes’s concession that thecogitoisnot entirely self-standing, but presupposes the meditator’s grasp of the conceptsinvolved, allows the following question to be raised. The extreme doubts of theFirst 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 someeven simpler matter, if that is imaginable’.⁴⁴But if a deceiving God couldpervert my intuitions regarding the simplest concepts of mathematics, why couldhe not also pervert my grasp of the fundamental concepts I need in order to reachthecogito? How, in short, can I trust my basic intuitions of the ‘intellectualsimple natures’ like the concepts of thought and of doubt, not to mention the‘common simple natures’, which include the concept of existence and also thefundamental rules of logic which seem necessary for any thought process at all toget off the ground?The correct answer to this conundrum, at least as far as Descartes’s ownstrategy is concerned, seems to be that the doubts of the First Meditation are notintended to be as radical as is often supposed. Doubts about our grasp ofmathematics are raised by the deceiving God argument, but a careful reading ofthe First Meditation confirms that doubts about our intuitions of the intellectualsimple natures are never entertained. Despite his talk of ‘demolishingeverything’, Descartes is chiefly concerned, as he says in the Synopsis,⁴⁵tochallenge our preconceived opinions concerning the nature and existence of thematerial 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 revealthe truths that cannot be doubted. The Cartesian project is not to ‘validatereason’,⁴⁶for such a project would be doomed to incoherence by the veryattempt to undertake it by using the tools of reason. Descartes cannot, and doesnot propose to, generate a system of knowledgeex nihilo. What he does proposeto do is to demolish commonly accepted foundations for knowledge, basedlargely on sensory experience and preconceived opinion, and utilize instead morestable foundations derived from the inner resources which have been implantedin each soul. The project is aptly summarized in Descartes’s dramatic dialogue,theSearch for Truth,which was perhaps composed around the same time as theMeditations:I shall bring to light the true riches of our souls, opening up to each of usthe means whereby we can find within ourselves, without any help fromanyone else, all the knowledge we may need…in order to acquire the mostabstruse items of knowledge that human reason is capable of possessing.⁴⁷THE ROLE OF GODIt is scarcely possible to underestimate the role played by God in thedevelopment of Descartes’s foundational project. The meditator’s awareness ofhis own existence is a curiously transitory insight: I can be sure I exist only solong as I am thinking.⁴⁸Admittedly, my awareness of myself as a thinking thingis quite indubitable and transparent: it surely could not turn out, Descartesobserves, 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, nogeneral progress towards a systematic structure of knowledge will be possibleunless I remove this residual doubt and establish ‘whether God exists and, if so,whether he can be a deceiver’.⁴⁹Deprived, at this stage of his inquiries, of any certain knowledge of the outsideworld, the Cartesian meditator has to establish the existence of God drawingpurely on the resources of his own consciousness. This is done by making aninventory of the ideas found within the mind. We cannot know at this stagewhether our ideas correspond to anything real, but it is clear that they are ‘likeimages of things’: that is, they have a certain representational content.⁵⁰Descartes now reasons that the content of each idea must have a cause; fornothing can come from nothing, yet ‘if we suppose that an idea containssomething which was not in its cause, it must have got this from nothing’. Inmost cases, the content of an idea presents no great explanatory problem: thecontent of many of my ideas, observes Descartes, could easily have been drawnfrom my own nature; other ideas (like those of unicorns) are simply fictitious, ormade up—put together by my own imagination. But the idea that gives me myunderstanding of ‘a supreme God, eternal, infinite, immutable, omniscient,omnipotent and the creator of all things’ is different: ‘all these attributes are suchthat the more carefully I concentrate on them, the less possible it seems that theycould 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, Godmust have ‘placed this idea within me to be, as it were, the mark of the craftsmanstamped on the work’.⁵¹Of the many problematic features of this argument, the most striking is theextent to which it relies on what are (to the modern ear at least) highlyquestionable assumptions about causation. A swift reading might suggest that allDescartes needs is the (relatively uncontroversial) deterministic principle thateverything has a cause (which Descartes expresses as the maxim that ‘Nothingcomes from nothing’). But in fact the argument requires much more than this: itis not just that my idea of God needsacause, but that its cause must actuallycontain all the perfection represented in the idea. It is ‘manifest by the naturallight’ claims Descartes, that ‘there must be at least as much reality in the causeas in the effect’, and hence ‘that what is more perfect cannot arise from what isless perfect’.⁵²What Descartes is in effect presupposing here is a theory ofcausation that is deeply indebted to the scholastic philosophical apparatus whichit is his official aim to supplant. According to the scholastic conception, causalityis generally understood in terms of some kind of property transmission: causespass on or transmit properties to effects, which are then said to derive theirfeatures from the causes.⁵³And this in turn presupposes that certain kinds ofsimilarity relations hold between causes and effects—in the words of thetraditional maxim which Descartes is reported to have quoted approvingly, ‘theeffect is like the cause’.⁵⁴This allegiance to traditional models of causality castsa shadow on Descartes’s bold professions of novelty—his claim to be ‘startingafresh’ in metaphysics. That might not matter in itself, had not the explicit goal ofthe whole enterprise been to build on solid foundations by demolishingunscrutinized preconceptions. Yet to read through the proof of God’s existencein the Third Meditation is to be confronted with a positive barrage of traditionaltechnical terms (‘substance’ and ‘mode’, and terms denoting various grades ofreality—‘formal’, ‘objective’, ‘eminent’ and the like), whose application thereader is asked to take as self-evident. The scrupulous caution andmethodological rigour which were employed earlier to establish thecogitoargument seem to dissolve away here. In short, when endeavouring to establishthe metaphysical foundations for his new science, Descartes seems unable to freehimself from the explanatory framework of his scholastic predecessors.⁵⁵But even if the details of Descartes’s proofs of God are taken on trust, deeperstructural problems remain. The most serious is what has come to be known asthe problem of the ‘Cartesian circle’ which was first raised by Descartes’s owncontemporaries, notably Marin Mersenne and Antoine Arnauld.⁵⁶The functionof Descartes’s proof of God is supposed to be to establish the possibility ofsystematic knowledge. If a perfect God exists, then the intellectual apparatuswhich he bestowed on me cannot be intrinsically inaccurate. Of course, I maymake mistakes from time to time, but this is due (Descartes argues in the FourthMeditation) to incorrect use of free will: I often rashly jump in and give myassent 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 ofavoiding error: ‘I shall unquestionably reach the truth if only I give sufficientattention to all the things which I perfectly understand, and separate these fromall the cases where my apprehension is more confused and obscure’.⁵⁷Provided Ikeep to this rule, I can achieve knowledge of countless things, including, mostimportantly, the structure of the physical universe—the ‘whole of that corporealnature which is the subject of pure mathematics’.⁵⁸Now the problem, in a nutshell,is this: if existence of a non-deceiving God has to be established in order for meto have confidence in the clear and distinct perceptions of my intellect, then how,without circularity, can I rely on the intellectual perceptions needed to constructthe proof of God’s existence in the first place? Descartes’s answer to thischallenge appears to be that the divine guarantee enables us to construct longchains of scientific reasoning but is not needed to establish the premises neededto prove God exists, since it is impossible to doubt these so long as we areactually attending to them.⁵⁹Unfortunately, however, the premises ofDescartes’s proofs for God seem to rely (suggested above) on a host of complexpresuppositions which have to be taken on trust: the transparent, self-confirmingquality which Descartes relied on to reach awareness of his own existence issimply not available in the elaborate causal reasoning needed to establish theexistence of a perfect non-deceiving God. If this is right, then Descartes’smetaphysical project must be counted a failure: the journey from indubitablesubjective self-awareness to systematic objective knowledge cannot becompleted. The challenge which Descartes puts into the mouth of an imaginaryobjector in his dialogueThe Search for Truthseems both apt and unanswerable:You seem to me to be like an acrobat who always lands on his feet, soconstantly do you go back to your ‘first principle’. But if you go on in thisway, your progress will be slow and limited. How are we always to findtruths such that we can be as firmly convinced of them as we are of ourown existence?⁶⁰THE ETERNAL VERITIESThe central place of God in Cartesian metaphysics should by now be more thanclear. But no account of this relationship would be complete without someattention to one of Descartes’s most perplexing doctrines —that of the divinecreation of the eternal truths. This is a doctrine which does not emerge explicitlyin theMeditations,but it surfaces in theRepliesto theObjections,and Descartesappears to have held it consistently throughout his life. He is reported to haveinsisted on it in an interview held two years before his death,⁶¹and he explicitlyasserted it, in his correspondence, as early as 1630:The mathematical truths which you call eternal have been laid down byGod and depend on him no less than the rest of his creatures…. They areall inborn in our minds just as a king would imprint his laws on the heartsof all his subjects if he had enough power to do so.⁶²Traditional theology maintained that divine omnipotence does not entail thepower to do absolutely anything, if ‘anything’ is taken to include even what islogically impossible. God cannot, on pain of absurdity, do what is selfcontradictory(e.g. make something which is both three-sided and a square); hissupreme power operates, as it were, only within the sphere of the logicallypossible.⁶³One might suppose that it is hardly an objectionable limitation on thepower of God that he cannot do nonsensical and incoherent things like creatingthree-sided squares; but Descartes’s conception of the deity is of a being ofabsolutely infinite power—a being who is immune to any limitation which thehuman mind can conceive. Thus, not only is he the creator of all actually existingthings, but he is the author of necessity and possibility; he was ‘just as free tomake it not true that the radii of a circle were equal as he was free not to createthe world’.⁶⁴Some of Descartes’s critics objected that this was incoherent, butDescartes replied that just because we humans cannot grasp something is noreason to conclude that it is beyond the power of God. God thus turns out, onDescartes’s conception, to be in a real senseincomprehensible:our soul, beingfinite, cannot fully grasp (French,comprendre;Latincomprehendere) orconceive him.⁶⁵From Descartes’s insistence on the ‘incomprehensibility’ of God, twoprofoundly disturbing problems arise for Cartesian philosophy. The first relatesto Descartes’s attempt to found his scientific system on secure metaphysicalfoundations. In the First Meditation, the possibility had been raised that thehuman intellect might go astray ‘even in those matters which it seemed toperceive most evidently’. And the doubt so generated extended, on Descartes’sown insistence, even to our fundamental intuitions about the mathematicalsimple natures. But what of the intellectual simple natures—the fundamentalconceptual apparatus needed for the meditator to arrive at knowledge of his ownexistence? We suggested earlier that if the doubt was allowed to go this far, thenthe very possibility of the meditator’s achieving any coherent reflection on hisown existence as a conscious being would be foreclosed at the outset. But thedoctrine of the divine creation of the eternal verities seems to entail that even ourgrasp of these basic concepts could be unreliable, in the sense that what isnecessary for us may not be necessary for God. A gap is thus opened up betweenthe basic processes of the human mind, and the true nature of things. And if wehave no reliable hold on the true logical implications of our concepts, if there isno sure route from what is ‘true for us’ to what is ‘true for God’, the entireCartesian journey from indubitable subjective awareness to reliable objectiveknowledge seems threatened at the outset.From this nightmare of opacity, an even more disturbing threat to theCartesian project seems to follow. If the structure of the fundamental principlesof logic is not ultimately accessible to human reason, but depends on theinscrutable will of God, then the very notion of ultimate truth, of something’sbeing ‘true for God’, turns out to be beyond our grasp.⁶⁶In his programme forscience, Descartes needs to insist constantly on the immutability and coherenceof the fundamental laws which govern the universe. By appealing to these laws,we are able, asserts Descartes, to derive a whole structure of necessaryconnections which operate in the world, and unravel a complex series of resultswhich describe the behaviour of matter in motion in accordance with the laws ofmathematics.⁶⁷But now, given that the rationale behind these necessities isultimately opaque to us, it seems to follow that the rationally ordered universewhich Cartesian science had hoped to reveal becomes in the end merely a seriesof arbitrary divine fiats; and against this background it is hard to see how the lawsof nature could ultimately be construed as anything more than brute regularities.In short, the doctrine of the divine creation of the eternal truths generates, fromour perspective at least, an ineradicable element of contingency in the system.The project of Cartesian rationalism, of uncovering a universe whose structure issupposed to be in principle transparent to the human intellect, now seemsradically unstable. At the heart of the system is a worm of doubt, an element ofarbitrariness which prefigures, if only faintly and in outline, the post-Humeanworld in which the working of the universe is in the end opaque to human reason.⁶⁸SCIENCE AND THE HUMAN MINDThe problems touched on in the previous sections have to do with the role of Godin Descartes’s conception of knowledge, and the status of scientific truth in theCartesian system. But there are certain features of the Cartesian programmewhich remain largely unaffected by these foundational issues. Whatever themetaphysical status of the ultimate laws governing the universe, Descartes could,and did, claim that his scientific approach was, in explanatory terms, botheconomical and comprehensive. These two features of Cartesian science are infact two sides of the same coin. The system could claim to be economicalbecause it subsumed a wide variety of phenomena under a very few simpleprinciples specifying the behaviour of matter in motion;⁶⁹and it could claim tobe comprehensive because it included hitherto separated categories of events—terrestrial and celestial, organic and inorganic, natural and artificial—under asingle explanatory apparatus.⁷⁰In his early work,Le Monde,Descartes aimed to describe the evolution of acomplete universe, starting from a chaotic initial configuration of matter inmotion and using simple mechanical principles to explain the subsequentformation of stars and planets, the Earth and the Moon, light and heat, the ebband flow of the tides, and much else besides. And he explicitly went on toinclude the human body as something which could be explained mechanically onthe 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 inmany different ways. But I am supposing this machine [of the humanbody] to be made by the hand of God, and so I think you may reasonablybelieve it capable of a greater variety of movements than I could possiblyimagine in it, and of exhibiting a greater mastery than I could possiblyascribe to it.⁷¹Descartes’s investigations into animal physiology (he performed frequentexperimental dissections during his long residence in Holland72) led him to theconclusion that many of the workings of the body could be explained byreference 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 inwhich gases or fluids are transmitted along systems of pipes and conduits. Therewas 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 forcomplex animal behaviour like pursuit and flight.⁷³The ways in which the beastsoperate can be explained by means of mechanics, without invoking any‘sensation, life or soul’;⁷⁴and even in the case of humans,we have no more reason to believe that it is our soul which produces themovements which we know by experience are not controlled by our willthan we have reason to think that there is a soul in a clock which makes ittell the time.⁷⁵Reflection led Descartes to conclude, however, that there were severe limits onthe power of mechanical explanations when it came to accounting for thecharacteristically human processes of thought and language. In theDiscourse,heargues that one could in principle construct an artificial automaton which wasindistinguishable from a dog or a monkey. But any such attempt to mimic humancapacities would be doomed to failure. A mechanical android, however complex,would betray its purely physical origins in two crucial respects: first, it couldnever possess genuine language, and second, it could never respond intelligentlyto the manifold contingencies of life in the way in which humans do. The first ofthese arguments, the argument from language, is a crucial weapon in Descartes’sstrategy of showing that human capacities are not just different in degree fromthose 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 changein its organs (e.g. if you touch it in one spot it asks what you want of it, andif you touch it in another it cries out that you are hurting it, and so on). Butit is not conceivable that such a machine should produce differentarrangements of words so as to give an appropriately meaningful answer towhatever is said in its presence, as even the dullest of men can do.⁷⁶The vital point here is that a mechanical system produces responses inaccordance 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 ofsituations.⁷⁷Hence it is ‘for all practical purposes impossible for a machine tohave enough different organs to make it act in all the contingencies of life in theway in which our reason makes us act’.⁷⁸The power of reason in human beings was thus, Descartes concluded,incapable of being explained by reference to the workings of a mechanicalsystem; a material structure, however complex its organization, could neverapproach the human capacity for thought and language. And hence, even in hisearliest scientific work, Descartes acknowledged a limit in principle to the scopeof physical explanation. The properties of stars and planets, rainbows andvapours, minerals, plants and animals could all be reduced to complexinteractions of matter in motion. But if God wanted to create a thinking humanbeing, he would have to create, in addition to all the physiological mechanismsof the brain and nervous system, a separate entity, a ‘rational soul’.⁷⁹The natureof this soul, and its relation to the physical world, was to become one ofDescartes’s principal preoccupations, when he came to develop his maturemetaphysics.THE INCORPOREALITY THESISTheDiscourse on the Methodcontains, in outline, Descartes’s central doctrineson the nature of the human soul. The central claim, which he introduces at theend 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 fromthe potentiality of matter, but must be specially created’.⁸⁰Anti-reductionismabout the human mind—the insistence that the phenomena of cognition andrationality are not reducible to physical events—is a thesis that still finds a gooddeal of support among present-day philosophers. But nowadays this thesis isgenerally advanced as a thesis about mentalpropertiesorevents:statementsabout such properties or events, asserts the anti-reductionist, cannot be replacedwithout remainder by statements about purely physical properties or events (e.g.statements about brain workings). But many modern anti-reductionists are still insome sensephysicalists;that is, they hold that mental processes and events mustbe realized or instantiated in the workings of physical systems, so that, if all suchsystems were destroyed, no mental happenings could occur. Descartes, however,takes a far more radical line. The Cartesian view is that the distinction betweenmind and matter is a matter of ontology: the mind is a distinct entity in its ownright, which operates, or can in principle operate, entirely independently of thematerial universe. This is the claim which has come to be known as Cartesian (orsubstantival) dualism: the mind is ‘really distinct’ from the body, a separate andindependent substance.Descartes’s initial argument for the incorporeality of the mind or soul (hemakes no distinction between the two terms81) arises from the meditative processwhich leads to thecogito. In becoming aware of his own existence, the meditatoris able to separate or bracket off all his beliefs about the existence of an externalmaterial world:Next I examined attentively what I was. I saw that while I could pretendthat I had no body, and that there was no world and no place for me to bein, I could not for all that pretend that I did not exist…. From this I knew Iwas a substance whose whole essence or nature is solely to think, andwhich does not require any place, or depend on any material thing, in orderto exist. Accordingly this ‘I’, that is the soul by which I am what I am,[ceMoi, c’est à dire l’Ame par laquelle je suis ce que je suis]is entirelydistinct from the body…and would not fail to be whatever it is even if thebody did not exist.⁸²It could be (and indeed was in Descartes’s own day83) objected that merelybecause I can think of ‘myself’ without thinking of my body, it does not followthat I could really exist if my body were destroyed. After all, I may (if I amignorant of the real nature of gold) be able to think of gold without thinking of itsatomic structure, but it does not follow that something could still exist as goldwithout that structure. Descartes’s position, however, is that if an object (in thiscase the thinking thing that is ‘me’) can be clearly conceived of as lacking agiven property (in this case having a body), then that property cannot beessential to the object in question.The phrase ‘whose whole essence or nature is solely to think’ is the key toDescartes’s reasoning here. Drawing on the traditional terminology of substanceand 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 standardscholastic view (derived from Aristotle) held that there is a large plurality ofsubstances, but Descartes reduces created substances to just two categories: mindand matter. The principal attribute of matter is extension (the possession oflength, 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 mathematicallydeterminable modifications ofres extensa,or ‘extended substance’.⁸⁴But now,just as all the properties of physical things are modifications of extension, so allthe properties of a mind (thinking, willing, doubting, desiring and so on) are allmodifications ofres cogitansor thinking substance. And Descartes took it asself-evident that the properties of thought and extension were not just differentbut utterly distinct and incompatible. ‘On the one hand,’ he later wrote in theSixth Meditation,I have a clear and distinct perception of myself, in so far as I am simply athinking, non-extended thing; and on the other hand I have a distinct idea ofbody, in so far as this is simply an extended, non-thinking thing. Andaccordingly it is certain that I [that is the soul by which I am what I am] isreally distinct from the body and can exist without it.⁸⁵By the time this full-blown argument is deployed in the Sixth Meditation,Descartes has more resources at his disposal than he had in theDiscoursewhenhe blandly observed that he could pretend he did not have a body without therebypretending that the ‘I by which I am what I am’ did not exist. In the SixthMeditation, God (whose existence is taken to have been proved at this stage) isinvoked 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 Ycannot be essential to X. The modern reader may feel uncomfortable here: surelyall the argument proves is that mind and body could conceivably existseparately, not that they are in fact separate entities. But it is precisely theconceivability of mind separate from body which Descartes relies on in order toestablish his dualistic thesis: ‘the mere fact that I can clearly and distinctlyunderstand one thing apart from another is enough to make me certain that thetwo things are distinct, since they are capable of being separated, at least byGod.’⁸⁶Whetherin factthe mind will exist after the death of the body issomething that Descartes is content to leave undetermined by reason: it is amatter of religious faith.⁸⁷It is enough that it is, as we should say nowadays,logically possiblethat it should exist without physical matter. That possibility,which Descartes takes himself to have demonstrated, is enough to guarantee theincorporeality thesis—that what makes meme,the conscious awareness ofmyself as ares cogitans,cannot depend on the existence of any physical object.What the above analysis suggests is that Descartes’s version of dualism standsor falls with the claim that the existence of mind without matter is at least alogical possibility. And a good many modern philosophers, however adamantlythey may be disposed to insist that mental properties are structural or functionalproperties of a physical or biological system (the brain, the nervous system),often concede that disembodied consciousness is at leastlogicallyconceivable.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 logicalcontradiction in conjoining (as Descartes does in theDiscourse) the twostatements (a) ‘I exist as a conscious being at timet’ and (b) ‘my body (includingmy brain and nervous system) does not exist at timet’. But this seems a veryweak argument. As Leibniz was later to observe (in a rather different context), itis not enough, to establish the coherence of a set of propositions, that one cannotimmediately detect any obvious inconsistency in them. For it is quite possiblethat a set of propositions which seems consistent on the face of it might turn outon further analysis to contain hitherto undetected incoherence.⁸⁸Borrowing theterminology of Karl Popper from our own time (and transferring it from therealm of philosophy of science to that of logic), we may say that claims oflogical possibility are falsifiable (by producing a contradiction) but notconclusively verifiable. Now admittedly, when we are dealing with very simpleand transparent truths (those of elementary arithmetic or geometry, for example),we may be entitled to be sure that there could be no hidden inconsistency whichwould undermine the logical coherence of a group of propositions. But when weare dealing with a phenomenon as complex and difficult as consciousness, itseems far from clear that we are entitled to declare, just by simple reflection, thatits 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 upour conscious life—‘internal’ sensations of pain and pleasure, and ‘external’sensations such as those of vision, touch, hearing, taste and smell—then it becomesdifficult to see how, if at all, these could be attributed to a disembodied entity.⁸⁹Such sensory events do not of course exhaust our conscious experience: thereremain what Descartes called the ‘pure’ cogitations of the intellect —thoughtsabout 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 individualconscious existence.⁹⁰In short, the logical possibility of the continuedindependent existence of theMoi—the ‘soul by which I am what I am’—is by nomeans as clear and straightforward a matter as Descartes invites us to suppose.THE RELATION BETWEEN MIND AND BODYDespite his insistence on the incorporeality of the mind, Descartes bothacknowledged, and made serious attempts to explain, the intimate relationshipbetween mind and body. That relationship, as he frequently pointed out, ismanifested in the facts of everyday experience:nature teaches me by these sensations of pain, hunger, thirst and so on, thatI am not merely present in my body as a sailor is present in a ship, but thatI am very closely conjoined and as it were intermingled with it, so that Iand the body form a unit.⁹¹Contemporaries of Descartes were puzzled by this admission: during aninterview which he conducted with the philosopher in the Spring of 1648, theyoung Dutchman Frans Burman asked him how the soul could be affected by thebody, and vice versa, given the supposed radical difference in their natures.Descartes answered that the point was ‘difficult to explain’, but that our owninner experience was ‘so clear’ that it could not be gainsaid.⁹²Reflections on the phenomenology of sensory experience help to identify whatDescartes is pointing to here. When we are thirsty, to take one of his examples,we do not merely have an intellectualunderstandingthat our body needs water;we experience a characteristic and intrusive sensation of a distinctive kind—themouth and the throat ‘feel dry’. What kind of event is this ‘feeling’? Accordingto the standard expositions of ‘dualism’ found in modern textbooks on thephilosophy of mind, to have a sensation like thirst is to be in a certain kind ofconsciousstate; and hence, feeling thirsty is, for the dualist, assignable to thecategory 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 thephenomena of ‘consciousness’ become that it takes some effort to realize thatDescartes’s own views about sensory experience are in fact rather different.Descartes doesnotsay that sensations are mental events simpliciter; on thecontrary, he explicitly says that ‘I could clearly and distinctly understand thecomplete “me” without the faculty of sensation’.⁹³Sensation, though it is aninescapable part of my daily experience, does not form an essential part of theres cogitansthat is ‘me’. Rather, Descartes explains, it is a ‘confused’ mode ofawareness which ‘arises from the union and as it were intermingling of the mindwith the body’.⁹⁴It emerges from this that Descartes’s universe is not quite as neat and tidy asthe label ‘Cartesian dualism’ tends to suggest. It is true that there exist, forDescartes, examples of pure thinking things—angels are his standard example—whose existence consists essentially and entirely in modifications of intellectionand volition; such beings are examples of ares cogitansin the strict sense. Onthe other side of the divide, there is pureres extensa,mere extended matterwhose every feature can be analysed as some kind of modification of thegeometrically defined properties of size and shape;⁹⁵the human body is anexample of a structure, or assemblage of structures, composed entirely ofextended matter. Buthuman beingsfit into neither of the two categories so fardescribed. 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 inbodies alone.Although the ‘union’ between body and soul is explicitly mentioned in theMeditations,the concept is left somewhat obscure, and it was not until he wasquestioned in detail by Princess Elizabeth of Bohemia that Descartes came toexamine in more detail exactly what it implied. We have, he wrote in a letter tothe Princess of 21 May 1643, various ‘primitive notions’ which are ‘models onwhich all our other knowledge is patterned’. He proceeds to list some of thecategories which he had much earlier labelled as ‘simple natures’: first, there are‘common’ notions, such as being, number and duration, ‘which apply toeverything 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 ofthought, which includes the conceptions of the intellect and the inclinations ofthe will’. All this is straightforward Cartesian doctrine. But now Descartes adds afourth category: ‘as regards soul and body together, we have the notion of theirunion, on which depends our notion of the soul’s power to move the body, andthe body’s power to act on the soul and cause sensations and passions’.⁹⁶Helater 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 singlething…. Everyone invariably experiences the union within himself withoutphilosophizing. Everyone feels that he is a single person[une seulepersonne]with thought and body so related by nature that the thought canmove the body and feel the things that happen to it.⁹⁷The notion that two different substances can unite to form a single thing is not, initself, obscure or problematic. We are familiar nowadays, for example, with theidea that hydrogen and oxygen can unite to form water; furthermore, this‘substantial union’ generates ‘emergent’ properties—water has properties suchas 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 togive 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 theessence of eitherres cogitansorres extensa. Nevertheless, Descartes himselfclearly felt that his notion of the ‘substantial union’ of mind and body presentedproblems. For mind and body, as defined throughout his writings, are not justdifferent, but utterly incompatible substances: in terms of their essentialcharacteristics, they mutually exclude one another, since mind is defined as nonextendedand 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 thesame time the distinction and the union between body and soul, becausefor this it is necessary to conceive them as a single thing and at the sametime to conceive them as two things, and this is absurd.⁹⁸CAUSAL INTERACTION AND OCCASIONALISMThe idea of the union of utterly heterogeneous items is not the only problematicfeature of Descartes’s theory of the mind and its relation to the body. Descartesfrequently talks in a way which suggests both that the mind has causal powersvis-à-visthe body (e.g. it can cause the body to move), and that the body hascausal powers with respect to the soul (e.g. passions and feelings are ‘excited’ bycorporeal events in the blood and nervous system). A great deal of Descartes’slast work, thePassions of the Soul,is devoted to examining the workings of thistwo-way causal flow between body and mind. The following is his account ofmemory:When the soul wants to remember something, this volition makes the[pineal] gland lean first to one side and then to another, thus driving theanimal spirits [the tiny, fast moving particles which travel through thenervous system] towards different regions of the brain until they comeupon 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 throughwhich the spirits previously made their way owing to the presence of thisobject have thereby become more apt than the others to be opened in thesame way when the spirits again flow towards them. The spirits thus enterthese pores more easily when they come upon them, thereby producing inthe gland that special movement which represents the same object to thesoul, and makes it recognize the object as the one it wanted to remember.⁹⁹What strikes the reader here is not so much the wealth of obsolete physiologicaldetail (modern readers will readily be able to substitute electrochemical events inthe cerebral cortex for Descartes’s movements of the pineal gland and ‘animalspirits’) as the way in which that physiological detail is expected to ‘mesh’ withevents in the non-physical realm of the soul. Descartes has managed to supply ahost of mechanisms whereby movements, once initiated in the pineal gland, canbe transferred to other parts of the brain and body; but he does not seem to havetackled the central issue of how an incorporeal soul can initiate such movementsin the first place. And the same problem will apply when the causal flow is in theother direction. Descartes devotes a lot of attention to the physiologicalmechanisms whereby bodily stimuli of various kinds cause changes in thenervous system and brain which ‘dispose’ the soul to feel emotions like anger orfear.¹⁰⁰But he does not explain how mere brain events, however complex theirphysiological genesis, could have the power to arouse or excite events in themental realm.Why exactly is thecausalaspect of the mind-body relation problematic forDescartes? The answer, in brief, is that throughout the rest of his metaphysicsand physics he seems to presuppose that causal transactions should be in somesense transparent to the human intellect. ‘The effect is like the cause’ was astandard maxim of the scholastics which (as noted earlier in this chapter)Descartes readily accepts.¹⁰¹In his causal proofs of God’s existence he relies onthe principle that the cause of an object possessing a given degree of perfectionmust itself possess as much or more perfection: whatever is found in the effect mustbe present in the cause. In physics, too, Descartes often seems inclined to requireexplanations that reveal transparent connections between causes and effects (inthe unfolding of the laws of motion, for example, a simple transmission model isinvoked—a cause transmits or passes on a determinate quantity of motion to itseffect).¹⁰²In all these cases, Descartes apparently wants to be able to appeal tosomething very simple and self-evident: if we could not ‘see’ how effectsinherited 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 nosuch transparency could be available in the mindbody interactions whichDescartes describes in such detail in thePassions of the Soul. Transparentconnections can be unfolded so long as we remain within the realm ofphysiology and trace how the stimulation of a sense organ generates changes inthe ‘animal spirits’ which in turn cause modifications in the movements of thepineal gland. But at the end of the story, there will be a mental event whichsimply ‘arises’ in the soul: the smooth progression of causal explanationsabruptly jolts to a halt. Whatever it is that bridges the gulf between the bodilyand 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.¹⁰³Descartes’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 away that various sensory experiences will ‘arise’ in it whenever the body towhich it is united is stimulated in a certain way. Thus, the mind has the innatecapacity of ‘representing colours to itselfon the occasionof certain corporealmotions [in the brain]’. There is, in effect, no genuine causal transmissionbetween mind and body; ‘nothing reaches the mind from external objects exceptcorporeal motions’; we make judgements about external things ‘not becausethese things transmit ideas to our mind through the sense organs, but becausethey transmit something which, at exactly the right moment, gives the mindtheoccasion to form these ideas by means of the faculty innate to it.’¹⁰⁴What wehave here is something powerfully reminiscent of developments later in theseventeenth century—the occasionalism of Malebranche, and the Leibniziantheory of ‘pre-established harmony’. And the lesson to be learned from this isthat the ideas of Malebranche and Leibniz were not, as is sometimes suggested,bizarre attempts to cobble together anad hocsolution to the problem of mindbodyinteraction which Descartes had bequeathed to Western philosophy; rather,they take their cue from Descartes’s own terminology, and his insistence that therelationship between physical events and mental phenomena must be explainedon the model of divinely decreed correlations rather than transparent causaltransactions. The heterogeneous worlds of mind and matter cannot, properlyspeaking, interact; only the decrees of God can ensure that they workharmoniously together.To conclude from this that Descartes’s theory of the mind is a failure would beeasy enough; but any sense of superiority that the modern commentator may feelshould be tempered by the thought that, even today, the relationship betweenbrain occurrences and conscious experience is very far from having beenelucidated in a coherent and philosophically satisfying way. What may be a morefruitful theme for reflection is Descartes’s own implicit recognition of the limitsof human knowledge. The Cartesian project for a unified system of knowledge,founded on transparently clear first principles, faltered, as we saw in the first halfof this chapter, when the human mind came to confront the incomprehensiblegreatness of God. And in a different way, the project faltered when it came tointegrating into science that most basic fact of human awareness—our everydayexperience, through our external and internal senses, of the world around us andthe condition of our bodies. To ‘explain’ that awareness, Descartes wasconstrained to admit that only the decrees of God, ultimately opaque to humanreason, will suffice. Causal transparency gives way to mere regular conjunction.If this, once again, seems to prefigure the thought of Hume, that should perhapsbe no surprise. For however much commentators may wish to present it as acontest between opposing teams of ‘rationalists’ and ‘empiricists’, the history ofthe early modern period is a continuous unfolding tapestry in which the threadsendlessly cross and re-cross. The picture that has come down to us is the work ofmany hands, but however we view it, there can be no disputing Descartes’s roleas one of its principal designers.NOTES1 AT VI 8: CSM I 115. ‘AT’ refers, by volume and page number, to the standardFranco-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 Englishtranslation:The Philosophical Writings of Descartes,vols I and II, ed.J.Cottingham, R.Stoothoff and D.Murdoch, and ‘CSMK’ refers to vol. III(TheCorrespondence)by the same translators and A.Kenny [6.2]. ‘CB’ refers toDescartes’ 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 theDiscourse(AT VI 41f.; CSM I 131).3 For the significance of this term (Latinpraejudicium), seePrinciples ofPhilosophy,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 thePrinciples of Philosophy(first published in Latin in 1644): AT VIIIA 14; CSM I 186. The simile is alsofound in other writers of the period, notably Francis Bacon (De augmentescientiarum,3, i).6Discourse 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 28June 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 othertwo were theOpticsand theMeteorology) illustrating Descartes’s method.12 AT X 163; CSMK 4. Descartes dedicated to Beeckman his first work, theCompendium Musicae,a study of the application of mathematical methods to theunderstanding of harmony and dissonance.13 cf.Discourse,Part Two (AT VI 19; CSM I 120) and Part One (AT VI 8; CSM I115).14 Descartes began work on hisOpticsandMeteorologyprior to 1630; cf. CSM I109f.15 See especially AT XI 26; CSM I 89. Descartes never publishedThe World.Although it was complete and ready to go to press in 1633, he suppressed the workon hearing of the condemnation of Galileo by the Inquisition for advocating theheliocentric hypothesis.16Regulae,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 toadhere unswervingly to a definite order, always starting from the simplest andeasiest things and never going beyond them till there seems to be nothing further tobe achieved where they are concerned’ (AT X 379; CSM I 20). See also Rule 5, whichinsists on the importance of ‘ordering and arranging the objects on which we mustconcentrate our mind’s eye if we are to discover some truth’ (ibid.), and Rule 6, whichasserts that the ‘main secret of the method is to distinguish the simplest things fromthose 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 fundamentalconcepts like ‘unity, existence and duration’ which may be applied either to thematerial or to the intellectual simple natures.21 AT X 421; CSM I 46.22 AT X 427; CSM I 49.23Discourse,Part One, AT VI 10; CSM I 116. Descartes implies that his resolution wasmade during his visit to Germany as a young man of 23, when he had his famousseries of dreams in the ‘stove heated room’ near Ulm on the Danube. These earlyreflections are described in Part Two of theDiscourse;see also the early notebooks(AT X 217; CSM I 4). InDiscourse,Part Three, Descartes suggests that afterpostponing these metaphysical inquiries he took them up again soon after arrivingin Holland (i.e. after 1629). We know from a letter to Mersenne that about this timehe actually began to compose a ‘little treatise on metaphysics’ whose principalthemes were ‘to prove the existence of God and that of our souls when they areseparated from our bodies’:je ne dis pas que quelque jour je n’achevasse un petittraité de Métaphysique lequel j’ai commencé étant en Frise, et dont les principauxpoints sont de prouver l’existence de Dieu et celle de nos âmes, lorsqu’elles sontséparées du corps(23 November 1630, AT I 182; CSMK 29).24 Discussing what title to give hisécrit de métaphysique(what we now know as theMeditations), Descartes wrote:Je crois qu’on le pourra nommer…Meditationes dePrima Philosophia;car je n’y traité pas seulement de Dieu et de l’âme, mais engénéral de toutes les premières choses qu’on peut connaître en philosophant parordre(letter to Mersenne of 11 November 1640, AT III 329; CSMK 158). Theterms ‘metaphysics’ and ‘first philosophy’ were of course not invented by Descartes;the latter comes from Aristotle who used it to describe fundamental philosophicalinquiries about substance and being, and the former from the name given by earlyeditors to Aristotle’s treatise on ‘first philosophy’ (the name ‘metaphysics’ comingoriginally from the fact that in collected editions of Aristotle this work wastraditionally placed after (Greekmeta) his physics). Descartes’s conception ofmetaphysics was significantly different from the Aristotelian one, however, notleast (as will appear) because of its radically subjective orientation. For adiscussion of crucial disparities between Aristotelian essences and Cartesian simplenatures, see J.-L.Marion, ‘Cartesian metaphysics and the role of the simplenatures’, in J.Cottingham (ed.)Cambridge Companions: Descartes[6.32].25 In particular by the Jesuit Pierre Bourdin; cf. Seventh Replies, AT VII 549; CSM II375.26 AT VII 12; CSM II 9.27Soliloquies,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 waslater to be for Augustine and Descartes, a paradigm of stable and reliable cognitionof the kind which sense-based beliefs could never attain. The term ‘rationalism’ isan over-used and problematic one in the history of philosophy, but it can serve toindicate interesting similarities between groups of philosophers: one suchindisputable similarity is the mistrust of the senses which runs like a clear threadfrom 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 asthat 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 complextwists 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 ofhis metaphysical views in Part Four of theDiscourse: considérant que toutes lesmêmes pensées que nous avons étant éveillés nous peuvent aussi venir quand nousdormons, sans qu’il y en ait aucune pour lorsqui soit vraie, je me résolus de feindreque toutes les choses qui m’étaient jamais entrées en l’esprit n’étaient non plus vraiesque 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 127.36Haud dubio igitur sum, si me fallit;&fallat quantum potest, nunquam tamenefficiet, ut nihil sim quamdiu me aliquid esse cogitabo.Adeo ut…deniquestatuendum sit hoc pronuntiatum,Ego sum, ego existoquoties a me profertur, velmente concipitur, necessario esse verum(AT VII 25; CSM II 17).37 The phrasing here is from theDiscourse,Part Four (AT VI 32; CSM I 127). Thenotion of the Archimedean point appears in the Second Meditation: ‘Archimedesused 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 phrasecogitoergo sumappears in thePrinciples of Philosophy,Part I, article 7; its Frenchequivalent,je pense, donc je suis,in theDiscourse,op. cit.38 AT VII 140; CSM II 100. For discussion of thecogitoargument, 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 theMeditations:‘I would not urgeanyone to read this book except those who are able and willing to meditateseriously with me’ (AT VII 9; CSM II 8). For the importance of the meditator’sactivity,see Wilson, op. cit., and compare J.Hintikka, ‘Cogito ergo sum: Inferenceor 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 SeePrinciples 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 14.45In 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 inDescartes’ 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: ATVII 35–6; CSM 24–5.50 Or what Descartes calls (using scholastic terminology) ‘objective reality’(realitasobjectiva). The more helpful reference to the ‘representational’ aspect of ideas issupplied in the 1647 French translation of theMeditations(by the Duc de Luynes)which was issued with Descartes’s approval.51 Third Meditation: AT VII 40, 45, 51; CSM II 28, 31, 35.52Lumine naturali manifestum est tantundem ad minimum esse debere in causa…quantum in ejusdem causae effectu…Hinc autem sequitur [non] posse…fieri…idquod 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 explanationspurely in terms of mathematical covering laws, offers the possibility of dispensingwith traditional models of causality; the opportunity, however, was not fully seizedby Descartes (see pp. 222–5). For more on Descartes’s conception of causality, andits influence on the philosophical history of the seventeenth and eighteenthcenturies, see N.Jolley,The Light of the Soul[6.19], ch. 3.54Conversation with Burman,AT V 156; CB 17. For more on the scholasticbackground to Descartes’s causal proof for God’s existence, see J.Cottingham, ‘ANew Start? Cartesian Metaphysics and the Emergence of Modern Philosophy’, inT.Sorell (Ed.)The Rise of Modern Philosophy[6.37].55 In the Fifth Meditation, Descartes offers a further proof of God’s existence, namelythat since God is defined as the supremely perfect being, all perfections, includingthat of existence, must necessarily be part of his essential nature:it is quite evident that existence can no more be separated from theessence of God than the fact that its three angles equal two right angles canbe separated from the essence of a triangle, or than the idea of a mountaincan be separated from the idea of a valley. Hence it is no less of acontradiction to think of God (that is a supremely perfect being) lackingexistence (that is, lacking a perfection) than it is to think of a mountainwithout 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 ofCanterbury in the eleventh century, but it had been strongly criticized by Aquinas,and its revival by Descartes was a source of considerable surprise to hiscontemporaries. For some of the objections raised by contemporary critics, see theFirst Set of Objections to the Meditations, AT VII 98; CSM II 70. For a discussionof 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 VII214; 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 circleobjection and Descartes’s reply to it, see especially A.Gewirth, ‘The CartesianCircle’ [6.45] and L.Loeb, ‘The Cartesian Circle’, in J.Cottingham (ed.)CambridgeCompanions: Descartes[6.32].60 AT VII 526; CSM II 419.61Conversation with Burman(1648): AT V 160; CSMK 343.62 Letter to Mersenne of 15 April 1630, AT I 145; CSMK 23; cf. Sixth Replies: ‘Goddid not will that the three angles of a triangle should be equal to two right anglesbecause he recognized that it could not be otherwise;…it is because he wills thatthe three angles of a triangle should necessarily equal two right angles that this istrue 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 25.65Notre âme, étant finie, ne le puisse comprendre ni concevoir(ibid.). For furtherdiscussion 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 SeePrinciples,Book II, art. 64.68 I use the term ‘post-Humean’ in accordance with what may be called the traditionalinterpretation of Hume as a philosopher who undermined the idea of science as thediscovery of necessary connections in the world. For an alternative interpretation,see J.Wright,The Sceptical Realism of David Hume(Cambridge, CambridgeUniversity Press, 1983).69 For the simplicity and economy claimed by Descartes for his system see the letterto Huygens of 10 October 1642 (AT II 797; CSMK 216) andPrinciples,Part IV,arts 199 and 206.70 For the breaking down of the barriers between terrestrial and celestial, seePrinciples,Part IV,passim;for the barrier between organic and inorganic, seeDescription of the Human Body(AT XI 226; CSM I 315); for that between naturaland artificial, seeTreatise on Man(AT XI 120f., CSM I 99f.).71Treatise on Man:AT XI 120; CSM I 99. Though published (after Descartes’sdeath) as a separate work, theTreatise on Manwas originally conceived byDescartes as part ofLe Monde. See further CSM I 79.72 He lived for a time in Kalverstraat in Amsterdam, where he obtained carcasses fordissection from the butcher; some of his later experiments in vivisection aredescribed in theDescription of the Human Body(AT XI 242f.; CSM I 317f.).73 AT VII 230; CSM II 161.74 AT VII 426; CSM I 288.75Description of the Human Body:AT XI 226; CSM I 315.76Discourse,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).78Discourse,Part Five, op. cit. For more on the strengths and weaknesses ofDescartes’s language argument, see J.Cottingham, ‘Cartesian Dualism: Theology,Metaphysics and Science’, inCambridge Companions: Descartes[6.32].79 In theTreatise on Man,Descartes compares the nervous system to the complex setof pipes and reservoirs found in a park with fountains and moving statues:Visitors who enter the grottos of these fountains…cannot enter withoutstepping on certain tiles which are so arranged that if, for example, theyapproach a Diana who is bathing they will cause her tohide in the reeds, and if they move forward to pursue her they will cause aNeptune to advance and threaten them with his trident.All these events happen purely mechanically, according to the ‘whim of theengineers who made the fountains’. But a human being is more than aphysiological system of pipes and levers:when a rational soul is present in the machine, it will have its principalseat in the brain and reside there like the fountain keeper who must bestationed at the tanks to which the fountain’s pipes return if he wants toproduce or prevent or change their movements in some way.(AT XI 131; CSMI 101)80Discourse,Part Five: AT VI 59; CSM I 141.81 cf. Synopsis toMeditations: ‘…l’esprit OH l’âme de l’homme (ce que je nedistingue point)…’(AT IX 11; CSM II 10).82Discourse,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 originalLatin 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 ofhuman 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 onMetaphysics,§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 theLateran 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 56.92Conversation 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 sensationand imagination are often singled out for special treatment by Descartes. Comparea passage earlier in the same Meditation, which asserts that imagination is not anecessary constituent of my essence as a thinking thing:vim imaginandi, proutdiffert a vi intelligendi, ad mei ipsius, hoc est ad mentis meae essentiam nonrequiri(AT VII 73; CSM II 51). For more on the ‘hybrid’ faculties, seeJ.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 astraightforward mode of extension (AT II 650; CSMK 217), but which, in thePrinciples,is said to be specially imparted to matter by divine action (seePrinciples,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.99Passions of the Soul,Part I, art. 42 (AT XI 360; CSM I 344). Descartes regardedthe pineal gland (orconarion) as the ‘principal seat of the soul’ and the locus ofpsycho-physical interactions; cf.Passions,Part I, arts 31 and 32.100 See for examplePassions,Part I, art. 39.101 See p. 211.102 SeePrinciples,II, 36 and 40.103 It should be noted that some recent commentators have argued that Descartes didnot in fact regard interaction between heterogeneous substances as problematic.See R.C.Richardson, ‘The Scandal of Cartesian Interactionism’ [6.51]. For criticismof this view, see J.Cottingham,The Rationalists[6.12], 212f. and 202.104Comments on a Certain Broadsheet:AT VIIIB 359; CSM I 304. Compare alsoOptics,Section Six: AT VI 130; CSM I 167. For more on the ‘occasionalist’elements in Descartes’s account of mind and body, see J.Cottingham, ‘Descartes onColour’,Proceedings of the Aristotelian Society90 (1989–90) Part 3, 231–46.BIBLIOGRAPHYOriginal language edition6.1 Adam, C. and Tannery, P. 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