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Descartes's Method of Doubt
Janet Broughton

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DESCARTES'S procedure in the Meditations on First Philosophy is extraordinary. In order to discover the fundamental principles of philosophy, he puts forward the dream argument and the deceiving God argument as reasons for doubt, and he vows to suspend judgment about everything to which those radical skeptical considerations apply. It is hard to imagine a present-day investigation of basic philosophical principles beginning in this way--say, Derek Parfit's Reasons and Persons or John Searle's Intentionality. Of course, there are many reasons why this is so. A few present-day philosophers are dissatisfied with all of the available ways of trying to rescue some sort of knowledge from radical skeptical attack. And many philosophers today would not expect that by showing how to answer the skeptic we would uncover fundamental principles of philosophy; they would expect that once the skeptic had been answered, our claims to knowledge would be much as they were before we raised the radical skeptical worries.

Descartes sees the problems and prospects of philosophy very differently from the way we do. In this introduction, I want to sketch a context that will allow us to develop a sympathetic appreciation of Descartes's extraordinary way of proceeding in the Meditations.

As a preliminary, I want to remind readers of a sequence of discoveries that Descartes claims to make in the Meditations. (I will be examining most of these steps in detail in the chapters to follow.) In the First Meditation, Descartes briefly raises ordinary grounds for doubting beliefs, but he gives his attention mainly to radical grounds for doubt. First he offers the dream argument (and a similar "lunacy" argument), which calls into doubt even the most evident of the beliefs we get from our senses--for example, my present belief that my hand is in front of me. Then he gives us the deceiving God argument (and a similar argument designed for atheists), which calls into doubt not just sense-based beliefs but also beliefs about what we grasp "clearly and distinctly," like the belief that two plus three equals five. Descartes resolves to suspend judgment about all of the beliefs to which these radical arguments apply, and at the beginning of the Second Meditation he worries that he has left himself in the position of suspending judgment about everything. He discovers, however, that "I exist" can somehow be salvaged, and indeed that he can also be certain of claims in which he attributes conscious states to himself. In the Third Meditation, he helps himself both to the causal principle that effects cannot be greater than their causes, and to the subsidiary principle that the cause of an idea must contain at least as much "formal reality" as the idea has of "objective reality." He then argues that given his certainty that he exists and has an idea of God, and his certainty that the causal principles are true, he can be certain that his cause, or creator, is God, a perfect being. This in turn assures him that his mind has been created so that his clear and distinct ideas are true. In the Fifth and Sixth Meditations, he draws upon a number of clear and distinct ideas to show that he can be certain that his beliefs in mathematics are true and that at least some of his beliefs about the world of material things are true too. During the course of these reflections, he recognizes that he cannot clearly understand the nature of his own mind or of material things unless he thinks of them as entirely distinct: mind as a nonextended consciousness, and material things as nonconscious extended things.


Many of today's students of Descartes will have read only the Meditations. While there are good reasons for this focus, it can lead to a lopsided picture of Descartes as a philosopher whose concern with "method" was above all a concern with a method for answering radical skeptical doubts and achieving absolute certainty. Descartes gave many more pages, and much more time, to describing methods of inquiry that did not begin with radical skeptical doubt, than to describing one that did.

He was hardly alone in his interest in methods of inquiring. Since ancient times philosophers had been deeply concerned with questions about method, and questions about "method" were hotly debated in the sixteenth and seventeenth centuries.1 But Descartes shared with many of his contemporaries a particular version of this concern. In the seventeenth century, philosophers were increasingly drawn to the belief that nature is fundamentally homogenous and has a simple, underlying order. This led them to suspect that someone was unlikely to achieve an understanding of nature by conducting a series of theoretically uninformed investigations of this phenomenon and that. Successful investigation would require methodic discipline imposed by a general theory of nature.2

Descartes's own interest in method rarely led him to concern himself with how to generate and analyze empirical data in answer to a scientific question. Rather, he was nearly always more interested in how to find the correct way to pose, or conceptualize, a problem,3 and he was convinced that there would always be some way of describing the route to this correct conceptualization that would equally well describe a route to insight into virtually everything else. Thus when he achieved success in one area, he sought to describe his procedure very generally so that he could turn to other areas and go on in the same way there as well.4 He found his successes in mathematics especially useful: in the Rules for the Direction of the Mind, the Discourse on the Method, and its appended essays in optics, geometry, and meteorology, Descartes represents himself as watching himself solve problems about quantities and their relationships, and then using his mind in this same distinctive way to solve problems in the physical sciences.

He apparently wanted his descriptions of these methods of discovery to enable his readers to use their minds in this distinctive way, too, though the general descriptions are so general that they often sound like platitudes--for example, the advice to "make enumerations so complete, and reviews so comprehensive, that [you can] be sure of leaving nothing out" (1:120; AT 6:19). It is easy to sympathize with Leibniz, who complained that Descartes's rules of method really just said, "Take what is needed; do as you ought; and you will get what you wanted" (1875-1890, 4:329). I imagine that most readers who learned something from Descartes about how to tackle problems in mathematics and physics found his actual explorations of specific problems much more helpful than the very general maxims of method.

When Descartes refers to the "method of universal doubt" (2:270; AT 9A:203), he means a method that begins with consideration of grounds for radical skeptical doubt. This is a distinctive method of inquiry, though in both the Rules and the Discourse, Descartes says things, as he strains for a high enough level of generality, that sound as though he thinks any decent method of discovery will require using the method of doubt. In the Rules he says, "We need a method if we are to investigate the truth of things" (1:15; AT 10:371), and most of the book is devoted to describing a general method for investigating many sorts of truths: mathematical, physical, psychological, and metaphysical. In Rule Two he calls upon us "to believe only what is perfectly known and incapable of being doubted" (1:10; AT 10:362), and that may sound as if he is propounding the method of doubt as at least a part of the method for getting at the "truth of things." He isn't, though. Instead of telling us to test our beliefs by raising the radical skeptical doubts, he is exhorting us to reject "merely probable cognition" (1:10; AT 10:362). He notes that by using this rule, we will straightaway accept the evident propositions of mathematics, and it may even be that we will accept such obvious nonmathematical claims as "Here is a hand."5 But the method of doubt requires us to suspend judgment about mathematical claims and obvious nonmathematical claims like "Here is a hand." Nowhere in the Rules does the general method of discovery involve the procedures dictated by the method of doubt.6

In the Discourse, Descartes does describe the method of doubt as the special method he used to investigate "the foundations of . . . philosophy" (1:126; AT 6:30), but the general method he describes there is not the method of doubt. True, the first of its four rules is "never to accept anything as true if I did not have evident knowledge of its truth: that is, carefully to avoid precipitate conclusions and preconceptions, and to include nothing more in my judgements than what presented itself to my mind so clearly and so distinctly that I had no occasion to doubt it" (1:120; AT 6:18). But Descartes goes on to say that his first applications of this rule (and the three others he gives) concerned problems in mathematics; a little later he adds that by using this general method he was able to solve "many problems" in optics and even meteorology (1:125; AT 6:29). Clearly he did not mean to be saying that he conducted these investigations by starting with, say, the dream argument.7

So Descartes envisioned methods for achieving knowledge that did not pose the challenge of radical skepticism, and indeed such methods occupied more of his attention over the years than the special method of doubt did.8 Of course, once we see this, we are bound to ask exactly when and why he thought we need to use the method of doubt. I will return to this question several times later in this book, and indeed later in this introduction. But for now let me briefly note two points.

The first is that Descartes associates the method of doubt with a special subject matter. It is the method he turns to when he begins "to search for the foundations of any philosophy more certain than the commonly accepted one," as he puts it in the Discourse (1:126; AT 6:30), and it is the method he uses for exploring "First Philosophy," as the full title of the Meditations tells us. The subtitle of the Meditations tells us something about this special subject matter: it concerns "the existence of God and the distinction between the human soul and the body." This has a misleadingly bland and pious sound to it. In fact, Descartes aims to establish all of the following substantive principles:

  1. God, a perfect being, exists;
  2. We ought to assent only to what we understand clearly and distinctly;
  3. The essential attribute of material things is extension, the continuous quantity studied in mathematics;
  4. The essential attribute of the human mind is thought, and the mind is a different substance from the human body;
  5. Human sense experience allows us to know that material things exist and affect our sense organs; it can usually be trusted to indicate what we should pursue and avoid; but although pat- terns of change in our sense experience do reflect patterns of change in the material things that affect us, we should not attribute to material things the qualities with which our sense experience directly acquaints us.

Not only are these substantive claims; as I will explain shortly, many of them were highly controversial in Descartes's time (as in ours). They are also, in an intuitive sense, foundational: they tell us what basic kinds of things there are, and how we can and cannot hope to learn something about them.

There is a second point I want to make here about the special subject matter that calls for using the method of doubt. Although Descartes seems to think that someone might well use the general methods of inquiry over and over again as he tackles new questions in mathematics or science, he imagines that each of us needs to use the method of doubt just "once in the course of . . . life" (2:12; AT 7:17; also 1:193; AT 8A:5; compare 1:30-31; AT 10:395-98), to restructure our basic picture of the world and of our own faculties for understanding it. This is not to say that he thinks using the method of doubt properly is easy. He thinks readers may need "several months, or at least weeks" to ponder the doubts he raises in the First Meditation, and then "at least a few days" to form distinct conceptions of the mind and the body (2:94; AT 7:130-31). So unlike our use of general methods of inquiry, our use of the method of doubt is supposed to produce a lasting change in the limited set of our fundamental beliefs.


So far I have been locating the method of doubt in relation to Descartes's general interest in methods of inquiry. I have not yet done anything to explain why he thought that a good way to grasp the principles of First Philosophy is to begin by raising radical skeptical doubts. My full account of Descartes's reasons for using the method of doubt will emerge in the chapters that follow, but let me begin here by presenting a common assumption about his reasons.

Many readers have assumed that it is Descartes's preoccupation with knowledge, along with his demanding conception of what knowledge consists in, that motivates and explains his use of the method of doubt. Such readers see Descartes as thinking first that mere reasonable belief, belief that does not amount to knowledge, is to be disdained by people who are using their minds properly. The idea that only knowledge should satisfy us completely is a compelling one, whose ancestry we can trace back at least to Plato; but, of course, what it comes to depends upon what "knowledge" is taken to be. On the assumption that I am spelling out, Descartes would be requiring of knowledge that it be something of which we can be certain. Why would he build this requirement into his conception of knowledge? Probably the best answer to this question would invoke Descartes's relation to mathematics. Looking at human beings' successes and failures in coming to understand truths, Descartes thought that in the natural sciences we had in earlier times achieved nothing of lasting worth. One century's theories would be overthrown by the next century's theories, and at any one time distinguished intellectuals would disagree among themselves about how to explain even the simplest phenomena. Only in mathematics could Descartes discern steady accomplishment, progress, and agreement, and he thought that we would succeed in other fields of inquiry only when we could pursue other sciences in much the same way that we pursue mathematics. And here is what impressed him about mathematics: "of all those who have hitherto sought after truth in the sciences, mathematicians alone have been able to find any demonstrations--that is to say, certain and evident reasonings" (1:120; AT 6:19).

So knowledge--really worthwhile cognition--requires certainty. And what is it to be certain? On the assumption I am spelling out, Descartes took it that the concept of certainty required ruling out not just ordinary, everyday grounds for doubt but also, if we stop to think about it, the radical skeptical grounds for doubt as well. That is, on this interpretative assumption, Descartes supposed that if we were really to reflect upon what it is to be certain, we would see that the radical skeptical grounds for doubt are a natural extension of the sorts of doubts we raise in everyday life, and that certainty requires ruling out not just the grounds of doubt that we ordinarily consider, but also some that do not occur to us in the course of everyday life.

So the picture would be this: we ought to pursue knowledge in our inquiries; knowledge requires certainty; and certainty requires ruling out radical skeptical doubts. If this picture were correct, it would provide a very simple way to explain why Descartes uses the method of doubt. He begins his inquiry into the principles of first philosophy by raising radical skeptical doubts so that he can show when and how we can rule them out. That will be the same as showing when and how we can have certainty, and that will be the same as showing when and how we can have knowledge, which is what we want to arrive at in our method-guided inquiry.

There is much about this reading of Descartes that I think is right. He was undeniably impressed with the success of mathematics and thought it was instructive. He also, I am sure, thought that a person who knew something was in a better cognitive state than someone who had only a reasonable belief. And there are at least a few places where he seems to be saying that a person who has knowledge must be able to defend his beliefs against radical skeptical attack. Consider this passage from the Second Replies:

The fact that an atheist can be 'clearly aware that the three angles of a triangle are equal to two right angles' is something I do not dispute. But I maintain that this awareness of his is not true knowledge, since no act of awareness that can be rendered doubtful seems fit to be called knowledge. Now since we are supposing that this individual is an atheist, he cannot be certain that he is not being deceived on matters which seem to him to be very evident. (2:101; AT 7:141)

Because he believes that God does not exist, the atheist will not assent to the claim that God exists and is not a deceiver. Descartes is saying that this leaves the atheist with no way to combat the deceiving God argument, and thus with no "true knowledge" in mathematics. So here Descartes seems plainly to be saying that a belief counts as knowledge only if the person who holds it can defend it against radical skeptical challenges (and, presumably, ordinary challenges too).

Despite all that is right about this reading, though, I think it gives us a mistaken impression of Descartes's concerns and strategies.9 My main reasons for saying this will come out in Part One of this book, where I take a closer look at the First Meditation and the way in which Descartes raises the radical skeptical doubts. Here I want mainly to draw attention to several points that should make us suspect that this reading is at least not giving us the full story about Descartes's reasons for using the method of doubt.

Let me first point out that this account of the atheist mathematician is in some tension with passages in which Descartes seems happy to allow that more general methodological maxims will safely guide us to knowledge in, say, mathematics or optics. In the Discourse, for example, he describes himself as "growing in the knowledge of the truth" (1:126; AT 6:30; trans. altered) before learning how to combat radical skeptical doubt.10 But even if Descartes's use of the method of doubt is closely tied to his conception of knowledge, it is not clear what explains what. Mightn't Descartes's use of the method of doubt be what explains the very demanding account of knowledge that he articulates in the Second Replies? Someone defending the assumption that the conception of knowledge explains the use of the method of doubt might reply that if we reverse the order of explanation, we will have to come up with some other way of explaining the use of the method of doubt. But there is another way to explain Descartes's use of the method of doubt; in fact, there are several.


Over the past two decades, a number of scholars have focused attention on the relation between Descartes's philosophical writings and his intellectual milieu: the science, theology, philosophy, and mathematics of his day. These scholars have stressed several very important aspects of the context in which Descartes used the method of doubt, aspects that may help us understand why he used it.11

First, we know that by the mid-1630s Descartes faced a particular rhetorical challenge. He was committed to a natural philosophy of mechanical corpuscularianism that was deeply opposed to the Aristotelian natural philosophy still entrenched in the Schools. He was shaken to learn, in 1633, that Galileo had been condemned by the Roman Inquisition for claiming that Earth moves around the Sun. He wrote to Mersenne that "if the view is false, so too are the entire foundations of my [natural] philosophy, for it can be demonstrated from them quite clearly" (3:41; AT 1:271). He decided not to publish Le Monde, the scientific treatise he had been working on for three years, and he was, understandably enough, very worried about whether and how he could advocate his natural philosophy without alienating a large and powerful segment of the learned world.

Against this background, we can easily see Descartes as intending the Meditations to hide and yet strengthen his advocacy of mechanistic corpuscularianism.12 He would be hiding his advocacy by considering just the general metaphysical underpinnings of his worldview, leaving undiscussed the controversial details of the view itself. He would be strengthening his advocacy by beginning with radical doubt and thus ostentatiously forgoing presuppositions about whether the scholastics or their opponents were right.

There is good support for such an account of his intentions. In 1640, he wrote to Mersenne about a plan to write a commentary on Eustache's Summa Philosophica Quadripartita, a compendium of scholasticism, but he asked Mersenne not to tell anyone about this plan until the Meditations was published, because it "might . . . hold up the approbation of the Sorbonne, which I want, and which I think may be very useful for my purposes, for I must tell you that the little book on metaphysics which I sent you [the Meditations] contains all the principles of my physics" (3:157; AT 3:233). A few months later, again to Mersenne, he wrote:

I may tell you, between ourselves, that these six Meditations contain all the foundations of my physics. But please do not tell people, for that might make it harder for supporters of Aristotle to approve them. I hope that readers will gradually get used to my principles, and recognize their truth, before they notice that they destroy the principles of Aristotle. (3:173; AT 3:297-98)

Understood in their historical context, passages like these suggest that Descartes had a strong motive for showing his readers how to use a method of discovery that not only led to the Cartesian metaphysical principles but did so in a way that did not rest upon offensive presuppositions.

Inquiry conducted according to the method of doubt is ostentatiously free of presuppositions. Descartes underlines this point in the Second Replies:

[T]he arguments in respect of which I ask my readers to be attentive and not argumentative are not of a kind which could possibly divert their attention from any other arguments which have even the slightest chance of containing more truth than is to be found in mine. Now my exposition includes the highest level of doubt about everything, and I cannot recommend too strongly that each item should be scrutinized with the utmost care [N]o one who restricts his consideration to my propositions can possibly think he runs a greater risk of error than he would incur by turning his mind away and directing it to other propositions which are in a sense opposed to mine. (2:112; AT 7:158)

In the Fifth Replies Descartes happily accepts Gassendi's description of the Meditations as a "project for freeing my mind from preconceived opinions" (2:241; AT 7:348). And the presuppositionless character of the method of doubt is at least part of the point of Descartes's rotten-apple metaphor:

[My critic] must have read somewhere in my writings that any true opinions which we have before we begin to philosophize seriously are mixed up with many others that are either false or at least doubtful. And hence, in order to separate out the true ones, it is best to begin by rejecting all our opinions and renouncing every single one; this will make it easier, afterwards, to recognize those which were true (or discover new truths) Now this is just the same as if I had said that if we have a basket or tub full of apples and want to make sure that there are no rotten ones, we should first tip them all out, leaving none at all inside . . . (2:348-49; AT 7:512; see also 2:324; AT 7:481)

So the method of doubt must have appealed to Descartes as a presuppositionless way to insinuate the foundations of his anti-Aristotelian, corpus-cularian, worldview.

A second motivation has been stressed recently by scholars who see Descartes as responding to the late Renaissance rediscovery of, and fascination with, ancient skepticism.13 Both Pyrrhonian and Academic skepticism were understood by sixteenth- and seventeenth-century intellectuals to be sweeping in scope and radical in character, leading to suspense of judgment about very nearly everything. Many of these readers found the considerations put forward by Cicero and by Sextus Empiricus to be persuasive.14 The times were right for radical skepticism: something very like the skeptical problem of the criterion was already being raised by Reformation and Counter-Reformation theologians arguing about the foundations of religious authority, and the entrenched conception of the world was already being rocked by reflection upon the voyages of discovery and the cosmological theories of Kepler and Copernicus. The learned world was ready for skeptical ideas and took them seriously.

Edwin Curley claims that "sometime around 1628 Descartes came to feel that pyrrhonian skepticism was a more dangerous enemy than scholasticism, and came to feel the force of skeptical arguments which cut against both his own position in the [Rules for the Direction of the Mind] and that of the scholastics" (1978, 38). Seen from this perspective, Descartes was indeed trying to "answer the skeptic," but not because he had built into the conception of knowledge a requirement of skeptic-proof certainty. Rather, other people were offering skeptical arguments and accepting skeptical conclusions. Descartes thought he could show that they were wrong to do so, and that in the course of correcting their mistakes he could at the same time show the underpinnings of his own worldview to be uniquely defensible.

This perspective helps to make sense of several passages in which Descartes wrote about skeptical ideas. In some of these passages he apologized for beginning the Meditations with skeptical arguments: he was not trying to "sell them as novelties" (2:121; AT 7:171); he hesitated to "reheat and serve this stale cabbage" (2:94; AT 7:130; trans. altered). I myself think that the radical skeptical arguments of the First Meditation are novelties, and I will return to this point in Part One. For now, what I want to note is that Descartes clearly thinks of skeptical ideas as commonplace. It should not surprise us to find that he wants to show how to refute them.

In fact, there are several passages in which Descartes explicitly recommends the method of doubt on the grounds that by using it he can show what is wrong with the arguments of the skeptics. Frans Burman reports that in his conversation with Descartes of April 16, 1648, Descartes said that people should not dig more deeply into metaphysical questions than he did in the Meditations, because he had dug as deeply as anyone needs to: "The author did follow up metaphysical questions fairly thoroughly in the Meditations, and established their certainty against the sceptics, and so on; so everyone does not have to tackle the job for himself, or need to spend time and trouble meditating on those things" (3:347; AT 5:165). In a passage in the Seventh Replies, Descartes seems to feel greater urgency in the task of answering the skeptic:

[I]t is wholly false that in laying down our foundations in philosophy there are corresponding limits which fall short of complete certainty, but which we can sensibly and safely accept without taking doubt any further. For since truth is essentially indivisible, it may happen that a claim which we do not recognize as possessing complete certainty may in fact be quite false, however probable it may appear. To make the foundations of all knowledge rest on a claim that we recognize as being possibly false would not be a sensible way to philosophize. If someone proceeds in this way, how can he answer the sceptics who go beyond all the boundaries of doubt? How will he refute them? Will he regard them as desperate lost souls? Fine; but how will they regard him in the meantime? Moreover we should not suppose that sceptical philosophy is extinct. It is vigorously alive today, and almost all those who regard themselves as more intellectually gifted than others, and find nothing to satisfy them in philosophy as it is ordinarily practised, take refuge in scepticism because they cannot see any alternative with greater claims to truth. (2:374; AT 7:548-49)

Radical skeptical arguments were being given and accepted by actual people. Descartes thought he could show what was wrong with the arguments these people were accepting, and what they should be accepting instead.15

So far we have seen two reasons why Descartes might have wanted to use the method of doubt, neither of them involving the interpretative assumption I sketched out earlier, the one that has Descartes appealing to conceptual connections among good cognition, knowledge, certainty, and refutation of radical skepticism. There are two more motivations to which I now want to turn.

Descartes begins the Synopsis of the Meditations this way:

In the First Meditation reasons are provided which give us possible grounds for doubt about all things, especially material things, so long as we have no foundations for the sciences other than those which we have had up till now. Although the usefulness of such extensive doubt is not apparent at first sight, its greatest benefit lies in freeing us from all our preconceived opinions, and providing the easiest route by which the mind may be led away from the senses. (2:9; AT 7:12)

On Descartes's own view of human life, our beliefs about ourselves and the world around us are pervasively distorted by a tendency, acquired in our earliest years, to cede too much authority to our senses (1:218-20; AT 8A:35-37). We assume that the things we see and touch are the basic sorts of things that there are, and we assume that they are much as we perceive them to be. Descartes thought these assumptions were false. Conscious things are basic sorts of things, but we cannot possibly see or feel them. Moreover, the basic components of physical things are bodies that are too small to see or feel, and even middle-size physical things do not really have the colors that we see, the warmth that we feel, and so on. We all make false assumptions about these matters, assumptions that are long held and deeply ingrained. We are capable of overcoming them, but this is very difficult for us to do. We need help, and that is what the method of doubt can provide.

So Descartes thinks that it will help us to inquire into the truth by starting with radical skepticism because this will loosen the grip of the senses upon our minds.16 If I am suspending judgment about whether anything I sense even exists, then I am, at least temporarily, freeing my thoughts from the distorting assumptions I have grown up with. This may subsequently allow me to discern and embrace principles that can replace the bad assumptions that have taken root in my mind.

Some of these new principles will concern the nature of physical things themselves, and Descartes the scientist is certainly eager to help us grasp that the essence of physical things is to be extended, and that all of their properties are just so many "modes" of extension, or ways of being extended. But he is equally eager for us to understand ourselves better. From the perspective of enlightened dualism, Descartes would describe our prereflective beliefs about ourselves as a jumble. We seem dimly to understand that what is special about us is that we have conscious states, but we mix that up with the further thought that we are corporeal things. We have no coherent way of putting these thoughts together, but we do not recognize our difficulty. Again, what can get us to see the problem, and prepare us for grasping a solution and sticking with it, is an inquiry that begins with radical doubt:

I wanted to prepare my readers' minds for the study of the things which are related to the intellect, and help them to distinguish these things from corporeal things; and such [skeptical] arguments seem to be wholly necessary for this purpose. (2:121; AT 7:171-72)

So Descartes sees a special heuristic value in beginning inquiry into first principles with radical skeptical doubts. (We might wonder why this isn't just an instance of the value of avoiding presuppositions. Reasons for treating this as a distinct motivation will emerge in Part One.)

The passage I have just quoted comes from Descartes's reply to an objection Hobbes made to the First Meditation: what, Hobbes had wondered, is the point of retailing these skeptical arguments? In addition to the heuristic point, Descartes mentions two others. One we have seen already: by giving the skeptical arguments, he can later show just how they can be decisively answered. But he continues with yet another reason for beginning with radical doubt: "partly I wanted to show the firmness of the truths which I propound later on, in the light of the fact that they cannot be shaken by these metaphysical doubts" (2:121; AT 7:172). This echoes the third reason in a slightly different trio of reasons he had given in the Synopsis: this extensive doubt "brings it about that we are not able to doubt further what we subsequently discover to be true" (2:9; AT 7:12; trans. altered). Both here and in the reply to Hobbes, Descartes is claiming a special sort of advantage that this doubt brings with it. The advantage does not lie in the presuppositionless character of the inquiry, nor in the satisfactions of answering irritating skeptical libertins, nor in the heuristic benefits of loosening the grip of the senses on our thinking. Rather, it somehow lies in the nature of the basis that we will have provided for the claims that we go on to discover.

Many readers will be inclined to think that this is where Descartes's demanding conception of knowledge comes in. They will take it that he is saying the method of doubt gives us the advantage of establishing truths in such a way that we can claim to have knowledge that they are true, where "knowledge" means, among other things, what we can defend against radical skeptical attack.

In Part One, I will be arguing that Descartes does indeed think there is a special advantage to establishing truths in such a way that we can defend them against radical skeptical attack. But this is not because he has a prior commitment to a very demanding conception of knowledge. Rather, I will argue, Descartes's use of the method of doubt enables him to execute a simple and coolly calculated strategy for establishing the first principles of philosophy he believes to be true. It is this strategic advantage that Descartes is alluding to in the Synopsis and in the reply to Hobbes, and once we see what it is, I believe, the appeal of the interpretative assumption I have begun questioning here will fully evaporate.

Before turning to the First Meditation, let me draw attention to another puzzle about the method of doubt that the Synopsis passage raises. Descartes says that using the radical doubts of the First Meditation will "bring it about that" (efficiat) our subsequent discoveries are established in an especially valuable way. How exactly will beginning with doubt do this? Descartes does not establish truths by first showing that the radical skeptical arguments are invalid or that they have false premises. But if he does not criticize the arguments in either of these ways, then their breathtaking scope suggests that there will not be any way to establish any truths if we take radical skepticism seriously at the outset. So why did Descartes think not only that knowledge of the truth could be salvaged from storms of skepticism, but that those very storms somehow brought the salvage about? My aim in Part Two will be to answer this question.

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