That is the story of Descartes' life, work and death. His true monument is the modern world, of which he is one of the founders. Every philosophy student reads him, and his is a household name. That is fame. Fame is acquired in many ways, not all of them involving merit; Descartes' fame rests on great merit, and is unlikely ever to fade so long as people read history and think about philosophy, and contemplate the lifetimes of those who made a difference to both.
Appendix I
A Note on Descartes' Philosophy
Descartes is studied in universities today for his philosophical (not his scientific) views, where "philosophy" has its present meaning as the collective label for metaphysics, epistemology (theory of knowledge), and ethics—and their various spin-offs. It is a sometimes confusing fact that in Descartes' day "philosophy" meant what is now called natural science, and the term "metaphysics" was used to denote what we now mean by "philosophy." This is why Descartes entitled his textbook of science The Principles of Philosophy. But here in this Appendix, as in the main body of the foregoing text, I use the word "philosophy" in its present-day sense to mean philosophy, not science.
Descartes' philosophy focused upon a central question in epistemology, and three related central topics in metaphysics. The epistemological question is: "What can I know with certainty?" The related metaphysical topics are: the fundamental constitution of the universe, the relation between its basic constituents, and the question of whether it includes a deity (and moreover, of a specific kind). As so often in philosophy, Descartes' answer to the central epistemological question stands in a defining relationship to the position he takes regarding the three related metaphysical topics. The answer to the epistemological question is: I can know with certainty that I exist, "I" being a mind or thinking thing. From there Descartes proceeded to argue that it can be proved there is a God, and moreover a good one; that error is the result of our own fallibility and pride; and that from all these considerations, responsible use of our cognitive powers will get us to truth. Along the way we are left with the difficult question of how mind and body interact but, since there is a good God, the fact that mind and body obviously do indeed interact can be left to the larger divine intellect to understand.
These central commitments of Descartes' philosophy are mentioned in due place in earlier chapters, and both they and the large debate that has come to surround them can be left to the many books and articles that the reader could consult to take matters further (see the Select Bibliography). But there are three interesting points to be made about Descartes' philosophy, one about its distinctive and famous starting point, the other two about Descartes' method of setting out his views, which might be useful to anyone proposing to embark on a more detailed study of his thought.
First, the idea behind the thesis for which Descartes is known even among those who know nothing else about him, namely, "I think therefore I am," is not original to him. The idea, in most explicit form, is that one cannot doubt one's own existence, which provides Descartes with what he was looking for, namely, something that one knows with absolute certainty. When St. Augustine wrote in the early fifth century that we can doubt everything except the soul's doubting ("On Free Will" II 3:7) he was even then not inventing a new idea, and presumably Jean de Silhon, who published his The Two Truths in 1626 containing the remark "it is not possible that a man who has the ability, which many share, to look within himself and judge that he exists, can be deceived in this judgement, and not exist," must have known St. Augustine's remark or—independently of that—the idea itself in the philosophical tradition.
Descartes certainly knew Silhon's work, which predates his own version of the "I cannot doubt my own existence" by between five and ten years, for he spoke approvingly of it, though he did not cite it. This is a little surprising given that Descartes owed even more than this to Silhon; for in the passage in which Silhon says that one cannot doubt one's own existence, he proceeded also to claim that God's existence can be proved from a knowledge of one's own existence—a crucial step for Descartes' thesis, given that the validation of one's responsibly acquired beliefs depends on there being not just a God but a good God, whose goodness is the guarantee that responsible use of cognitive faculties will lead to truth; a good God would not endow us with such faculties yet lead us astray—as the "evil demon" hypothetically does in the first Meditation to generate the swingeing doubt Descartes needed in order to get his project going.
Secondly, a striking fact about Descartes' philosophical writing is that it all takes a distinctively autobiographical form. One reason for this, no doubt, is that this form came naturally to him; but— more importantly—it was particularly suitable to his aims, for it is a conversational method of exposition which allowed him to explain his points by showing how he himself had arrived at them. There is a clever angle to this, of which Descartes was, of course, fully aware. It is that the reader is thereby made to take the point of view of the thinker of the thoughts in question—to become the denotatum of the first person pronoun "I"—and therefore to feel the convincing power of those ideas from the viewpoint of how they were arrived at. This was especially significant for Descartes' views because his system is such that it requires the individual consciousness to be convinced of the truth of what it thinks from within the privacy of its own experience, for it starts from a consideration of the contents of its private consciousness, and therefore has to find reason to trust what (appears to be) conveyed into it, by experience and reason, from an external universe.
This starting point—the Cartesian starting point of private data, from which a route to an external world has to be under-pinned by a guarantee of certainty lest it be an illusion created by perceptual or ratiocinative error, or the mischief of a malign demon bent on making us believe nothing but falsehoods—was accepted by all Western philosophy until Dewey, Heidegger and Wittgenstein in the twentieth century, and was the source of endless difficulty, as was the dualistic commitment (the mind-body division) of Descartes' metaphysics. For although Descartes laboured, most notably in his Meditations on First Philosophy, to provide a guarantee for the route from private experience to public world, few if any of his successors could accept what he offered as guarantee, which was: the goodness of a God. (Two large assumptions have to be accepted here: first, that there is a God; and secondly, that it is good.) So Descartes had bequeathed his successors an intractable problem to which no response seemed plausible, except to the individual proposers of the various solutions that were offered in epistemology: by John Locke and Bishop Berkeley, by Bertrand Russell and A. J. Ayer, and by others in between and since.
Thirdly, the reason why Descartes was such a repetitive writer— his three main works, the Method, the Meditations and the Principles, all iterated the same few basic philosophical claims—is that he was especially anxious to show that his scientific views—Copernican, materialist and mechanistic as they are—did not controvert the fundamentals of the Christian faith, but were consistent with it. It happens that his endeavour was one of the helps towards freeing science from the proscribing interference of religion, even though in his own day, and for a time afterwards, his desire to be believed on this score went unsatisfied by the people he most wished to convince: namely, the church authorities and the Jesuits. As he was keen to point out repeatedly, his metaphysics (his philosophy) was essential as a basis for his science—not in the sense that the latter followed from it, but because the science was licensed by the metaphysics in orthodox terms. His philosophy was thus a preface to his science; it is an irony, though only a minor one after all, that what is left of Descartes in the world of thought is that preface alone, for his science was very soon superseded by Newton and all that has followed from Newton's work.
Among the most discussed aspects of Descartes' thought are the sceptical arguments he used in applying his method of doubt, his insistence on the essential difference between mind and matter, and his reliance on the goodness of a deity to serve as a gua
rantee of our enquiries. Some comments are called for on each of these, given their centrality to Descartes' philosophical enterprise.
Descartes' "method of doubt" involved setting aside any belief or knowledge which admitted of the least possible doubt, however improbable or absurd that doubt might be, to see what if anything was left behind. If anything was left behind, it would be so precisely because it was invulnerable to doubt: it was certain. Since Descartes' aim in the Meditations was to discover what can be known with certainty, the method of doubt is crucial, for it is the route to his goal. Trying to take each of our beliefs or knowledge claims and individually subjecting them to scrutiny would be an impossibly long task, so Descartes needed a completely general means of setting aside the whole corpus of dubitable beliefs, however unlikely their alleged dubitability. This he sought to achieve by employing sceptical arguments.
It is important to note that Descartes' use of sceptical arguments does not make him a sceptic. Far from it; he used them merely as an heuristic device to show that we indeed have knowledge. He was therefore a "methodological sceptic" rather than a "problematic sceptic," by the latter term meaning someone who thinks that sceptical problems are serious and pose a genuine threat to our ambition to acquire knowledge. It happens that many philosophers since Descartes' time have felt that he did not provide an adequate answer to the sceptical doubts he raised, and that therefore scepticism really is a problem. Descartes himself emphatically did not think so.
The sceptical considerations Descartes used are mentioned briefly in the main text, but merit iteration here. The first of them is a reminder that our senses sometimes lead us astray; perceptual misjudgements, illusions, and hallucinations can and occasionally do give us false beliefs. This might prompt us not to place reliance on what we think we know by means of sense-experience, or at the very least to be cautious in reposing confidence in it as a source of truth. But even so, said Descartes, there would be many things I believe on the basis of my current experience—such as, for example, that I have hands and that I am holding a piece of paper in them, that I am sitting in an armchair in front of a fire, and the like, to doubt which would seem to be madness, even given the senses' frequent unreliability.
Would it really be mad to doubt such things? No, said Descartes— and he here brought his second argument into play—for I sometimes dream when I sleep, and if I am now dreaming that I am sitting in front of a fire holding a piece of paper, my belief that I am so doing is false. To be able to be certain that I am sitting thus, I would have to be able to exclude the possibility that I am merely dreaming that I am sitting thus. How is that to be done? It seems very hard, if not impossible, to do it.
But even if one were asleep and dreaming, he continued, one could know that, for example, one plus one equals two. Indeed there are many such beliefs that could be known to be true even in a dream. So Descartes introduced a much more swingeing consideration: suppose that instead of there being a good God who wishes us to know the truth, there is by contrast an evil demon whose whole purpose is to deceive us in all things, even about "one plus one equals two" and all such other apparently indubitable truths. If there were such a being, one would have a completely general reason for doubting everything that can be doubted. And now we can ask: suppose that there is such a being; is there any belief that I nevertheless cannot doubt, even if the deceiving demon makes every belief I have false, if it is possible for it to be false? And as we know, the answer is yes, there is an indubitable belief: it is that I exist.
Some critics of this procedure have argued that the sceptical arguments employed by Descartes do not work. They criticise the dreaming and evil demon argument on a variety of grounds—for respective examples, that there are indeed criteria that enable us to distinguish between dreaming and waking states; and that the evil demon hypothesis is far less plausible than most of the beliefs (such as that one plus one equals two) it is supposed to call into question. But such attempts to show that Descartes' method of doubt cannot get off the ground are misplaced. The sceptical arguments employed in the method of doubt do not themselves have to be plausible or sustainable. They may indeed be far less plausible than what they impugn; but that does not matter. They are simply a device, an heuristic, something that helps one to see how it is that when one says "I exist" it cannot but be true. Given that in any case the aim of the Meditations was to demonstrate what can be known with certainty, almost any heuristic that made it possible to expose certainties would do equally as well.
Criticisms of the sceptical arguments Descartes used are more pertinent if those arguments are employed as part of a "problematic" sceptical attack on the possibility of knowledge or reliable belief. If a sceptical argument is less plausible than what it is used seriously to call into question, that is a prima facie reason for suspecting it. We can in this case legitimately ask whether sense-perception is as unreliable as the argument alleges; whether the idea of a deceiving demon is a coherent one; whether the concept of error would make sense if there were never anything to contrast it with, namely, sometimes being right or knowing the truth; whether the formulation of sceptical doubts is itself possible unless we already know something to be true, for example that responsibly employed reasoning is reliable and that we know the meaning of the words we use in framing the sceptical doubt; and so forth. But none of this applies to Descartes' argument in the Meditations, in which the invocation of sceptical considerations is merely a device, and does not have to survive scrutiny of this kind to do the work required of it.
The second great talking point in Descartes'philosophy, the mind-body problem, is the source of an immense debate in philosophy and more latterly also in psychology and the neurosciences. It is one of the most important questions still facing human enquiry. Put at its simplest, it asks: what is mind, and what is the relation of mind to the rest of nature? How should we best understand common-sense concepts of such mental phenomena as belief, desire, intention, emotion, reason and memory? How does the grey matter of the brain give rise to our rich and vivid experiences of colour, sound, texture, taste and smell?
Descartes gave the mind-body problem an especially sharp focus by arguing that everything that exists in the world falls under the heading either of material substance or mental substance, where "substance" is a technical term denoting the most basic kind of existing stuff. He defined the essence of matter as extension (that is, occupancy of space), and the essence of mind as thought. Matter is thus extended stuff, mind is thinking stuff. But by making matter and mind essentially different in this way, he raised the seemingly insuperable problem of how they interact. How does a bodily event like pricking oneself result in the mental event of feeling pain? How does the mental event of thinking "it's time to get up" cause the bodily event of rising from bed?
Descartes himself did not have an answer, and his successors had to resort to heroic solutions to the problem his theory had bequeathed. Their strategy was to accept dualism but to argue that mind and matter do not in fact interact, their appearance of doing so being the result of the hidden action of God; such were the views of Malebranche and Leibniz, reported in the main text above.
A much more plausible alternative, however, is monism: namely, the view that there is only one substance. Three possibilities rise to the fore. One is that there is only matter. The second is that there is only mind. The third is that there is a neutral substance which gives rise to both mind and matter. Each of the three has had proponents, but it is the first option—the reduction or annexation of all mental phenomena to matter —which has been most influential.
One materialist approach is the "identity theory," which asserts that mental states are literally identical with states or processes in the brain. In its earliest form, it asserted that occurrences of mental phenomena are nothing other than types of brain occurrences, but this was quickly seen to be too sweeping, for a particular mental event (for example, a mental image of the Eiffel Tower) might in my brain be instantiated in o
ne set of cells, in yours another.
On the basis of this theory, a number of philosophers currently maintain that, as neuroscience advances, we will be able to eliminate the old-fashioned and imprecise mental vocabulary we standardly use. Research in neurology and cognitive science has built an overwhelming case for accepting a very intimate relation between mental and neurological phenomena. Neuroscientists now have highly detailed empirical knowledge of brain function and its relation to mental activity, and are able to locate the seat of many conscious processes in precisely defined brain structures.
But these advances only serve to correlate brain activity with mental occurrences; they do not explain how the former actually produces the latter. Given the persistent difficulties in identifying that relation precisely, various strategies are proposed. One is to accept that our ways of talking about mental and physical phenomena are irreducibly different, even though they are about the same thing. Imagine, for example, how sociologists and physicists would respectively describe a football game, each focusing upon features which his particular science can address to describe the same thing.
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