I'm Peter Adamson, and you're listening to the History of Philosophy podcast, brought to you with the support of the philosophy department at King's College London and the LMU in Merrick. Online at historyofphilosophy.net. Today's episode, Perchance to Dream, Descartes' Skeptical Method.
Some years ago I attended a performance of Shakespeare's Hamlet in London. Watching it, I was struck by the unusual challenge it must pose to the actors. It's packed with familiar quotations, to the point that it seems almost impossible to make the dialogue seem fresh. It's no easy feat to deliver the line, to be or not to be, or, alas, poor Yorick, and get the audience to feel as if Hamlet is saying this only just having thought of it.
What was once a newly written play has over time become something more like a greatest hits compilation. Rereading Descartes' Meditations, I had a similar sensation. Once original, but now clichés are clear and distinct ideas. The evil demon that may be feeding us false beliefs, the contemplation of a piece of wax, imagining that people in the street are automata, hidden under cloaks and hats.
And, of course, cogito ergo sum. I think, therefore, I am quite possibly the most famous single sentence in all of philosophy. A pleasing trivia fact is that these exact words do not appear in the Meditations, though they do in other writings by Descartes. Still, the cogito argument does play a key role, or even the key role, in the meditations. If that is, it is really an argument. We'll come back to that.
I think that comparison to Hamlet is an apt one, even beyond the over-familiarity of the text, because a big part of the extraordinary success of the Meditations is its literary artistry. It has the gripping quality of investigative drama. Descartes casts himself in the role of the meditator, the kind of philosophical private detective who's going to solve the biggest mysteries of all without leaving his study.
Through incidental examples, we get a concrete sense of the scene. The meditator is in a dressing gown, paper in hand, next to a glowing fire. His aim is to discover what, if anything, he knows is a matter of absolute certainty. The plot of the meditations is that the meditator puts all his beliefs under suspicion, then, step by step, restores his conviction in their reliability.
As critics at the time immediately pointed out, many of the individual arguments were not original to Descartes. His reasons for doubt go back to antiquity. Perhaps I am insane, or dreaming, or a supernatural power like God or the evil demon is deceiving me. One of Descartes' proofs of God's existence is just the classic ontological argument, and as for the Cogito argument, it can be found in Augustine.
After this parallel was pointed out to him by Messin, Descartes claimed it was a happy coincidence, but he admitted that numerous other moves in the meditations were derivative. the skeptical worries in particular might seem like stale cabbage. Still, he needed to reheat them and serve them up to the reader nonetheless, as part of a philosophical method that was genuinely new. Our question in today's episode is how and why.
As we launch this investigation of our own, we should look for clues in Descartes' previous writings. These show that Descartes was intensely interested in philosophical method. His first published work was called Discourse on the Method. It appeared in 1637 and anticipates some of what we find in the 1641 meditations, including the vow never to accept any proposition without evident knowledge of its truth.
Already in the 1620s, Descartes was at work on rules for the direction of the mind. It appeared only posthumously, first in a Dutch translation, and then finally the Latin original, only in 1701. The Rules is a short but difficult text. It was composed over years, during which time Descartes' views evolved. And then there's the new manuscript that has come to light only recently, which is significantly different from the 1701 version.
It's ironic that the rules has such a complex history, because its aim is to present a straightforward and simple method for all manner of intellectual inquiry. It's an approach that Descartes first adopted in mathematics and now wants to use for all the sciences. He even refers to the ancient mathematicians Papus and Diophantus as pioneers in the method, breaking with his usual vow of silence as far as his sources go.
He might also have mentioned the Aristotelian scholastics at Padua, but of course he doesn't. Like Zavarella and other Paduan thinkers, Descartes divides his method into two parts, which he calls analysis and synthesis. Analysis is of particular interest, because Descartes would later say that this was the method used in the meditations. Analysis begins with familiar phenomena that we want to explain and breaks them down into simpler parts.
Ultimately, we want to arrive at general ideas or principles. These are grasped directly through what Descartes here calls intuition, which he defines as the indubitable conception of a clear and attentive mind that proceeds solely from the light of reason. These principles will later appear as the clear and distinct ideas of the meditations.
Having isolated them through analysis, we then turn around, as it were, and perform synthesis. This means retracing our steps and showing that the particular phenomenon we wanted to explain originally can indeed be accounted for using the principles we found. As Descartes puts it in the discourse, I take my reasonings to be so closely interconnected that just as the last are proved by the first, which are their causes, so the first are proved by the last, which are their effects.
Obviously, this is all terribly abstract, and it would be nice to have an example. Actually, here are two. One, taken from the rules itself, of course concerns mathematics. Descartes mentions the problem of finding the proportional mean between two numbers, as in 3 is to 6 as 6 is to 12, or 5 is to 10 as 10 is to 20. Here we see that an unlimited number of mathematical problems can be reduced to just one idea, the proportional mean. All these problems will have the same kind of solution.
Furthermore, the idea of a proportional mean is clearly distinguished from other nearby ideas, for instance, ratio, like 3 is half of 6. This is what distinct means in the phrase clear and distinct, that this idea has been distinguished from all other ideas. elsewhere, Descartes offers the example of a triangle to illustrate this, which might actually be a bit more helpful.
Probably you remember being at school and finding the area of a complex shape by breaking it down into triangles whose individual areas can be calculated easily. The triangle is such a clear idea that it doesn't call for further analysis. Also, you aren't going to confuse a triangle with a line or a square, so it is distinct. What would be an example of an idea that is not clear and distinct? Well, in the meditations, Descartes offers the case of coldness.
It is unclear and indistinct, because it might be a positive property of a body, or might just be the absence of heat. We don't even know if it is a thing or a non-thing. With this bad case of cold, we come from mathematics to natural philosophy. Our second illustration of Descartes' method also comes from this area. In his withheld treatise, The World, one of the topics that I tackled was the reflection and refraction of light.
He alludes to this topic in the rules, saying that to understand the behavior of light, we need to consider the idea of a natural power. The point being that light must involve a natural power, so we need to analyze it into this more general and simple idea, and then use that idea to deduce, by synthesis, why light is behaving as it does.
Here in the rules, we don't get further illumination on the question, but in the writings on natural philosophy, Descartes gives a series of analogies for how light may work. He compares the ray of light to a walking stick and a tennis ball. It is like a walking stick because its motion conveys an effect from source to destination immediately.
just as you can poke a stone with a stick and the stone will move as soon as your hand does. So the light source is seen simultaneously with the light rays impact on your eyes. That impact then triggers a further motion in the optic nerve, which is connected to the brain.
Notice that this explanation of vision is entirely mechanistic and involves no qualities, such as color. That fits with what we learned about Descartes' views of perception, according to which our subjective visual experience arises from the causal interactions of microscopic bodies. As for why light is like a tennis ball, this is because the tiny particles of light bounce off surfaces the way a ball thrown at the floor will leave the surface at the same angle.
This just applies Descartes' laws of motion. When the ball hits an object it cannot overpower, its motion is deflected along a straight line. Light works the same way when it reflects off a mirror. With this analogy, then, we are again using analysis to get down to the simple idea of reflection at equal angles, and then to the still simpler idea of motions caused by collisions.
We can then use synthesis to show that these concepts do indeed explain the particular case of a mirror image or reflected beam of light. that step is crucial because it establishes that the principles we found by analysis really do account for the phenomenon in question. The whole procedure seems very abstract, like something Descartes could have come up with while sitting by the fire in his dressing gown. And in a way, that's true.
but there's an important place for experimentation in his philosophy because it is needed to validate the explanation we have come up with. Real measurement will verify that the angles of reflection are as predicted. One reason we need to do this sort of test is that multiple causal accounts could be consistent with our principles. So we need to do some empirical investigation to decide which account accurately describes the world.
As I say, similar ideas about method had been developed amongst Aristotelians. It would even be possible to frame Descartes' story about reflected light in syllogistic form, as the scholastics like to do. Every moving body bounces off other bodies at equal angles. Light is a moving body, therefore light bounces off other bodies at equal angle. But Descartes is emphatic that his method is not so logistic. Instead, it deploys comparisons which give us the exact knowledge of the truth.
Comparing reflected light to a tennis ball draws the mind to the clear and distinct idea of reflection, which is grasped through intuition or the natural light of reason. This may sound a bit arbitrary and dogmatic. Come up with some analogies, announce that they've led you to some evident principles, and advise anyone who still disagrees to think about it harder. As Leibniz put it in a mocking summary of Descartes' method, take what is needed, do as you ought, and you will get what you wanted.
The early Descartes could defend himself against this charge to some extent. The empirical verification part of the method would help, for starters. And also, he does not underestimate the difficulty of the procedure. He stresses the need for training, as by going over an analysis and synthesis carefully and without interruption to accustom the mind to making these connections.
Still, it would be nice if we had a better way of ensuring that our rock-solid principles really are rock-solid and that they lie beyond all possible doubt. Presumably, the best way to do that would be to try to doubt them and see what happens. This brings us back to the meditations and its revolutionary method of radical doubt.
Descartes told Nassim that the purpose of the work was indeed to provide all the foundations of my physics, but that this purpose was left unstated to avoid calling attention to the fact that the meditations destroys the principles of Aristotle. So, the arguments of the meditations aimed to make good on an ambition already stated in his rules, where he declared, We resolve to believe only what is perfectly known and incapable of being doubted.
And remember, he told Marcin that the sole method of the meditations is analysis, so it must involve a search for principle. But is this his only motivation for adopting a stance of radical doubt? How would radical doubt lead us to principles exactly? And what is radical doubt anyway? These questions have attracted a staggering amount of commentary from modern-day Descartes scholars, which I'll do my best to summarize for you without any claim to completeness.
One starting point would be the prevalence of skepticism in Descartes' historical context. We know from earlier episodes that, not long before Descartes, several French thinkers had been reviving the ideas of the ancient skeptics and devising skeptical arguments of their own.
Montaigne is perhaps the most important here. Indeed, the setup of the meditations, an intelligent man sits alone pondering what he can know and what he cannot, is highly reminiscent of Montaigne sitting in his tower and doing exactly the same thing. The Meditations is like something Montaigne might have written if he were extraordinarily confident, instead of charmingly diffident, and if he didn't have a penchant for quoting sources.
Other skeptical authors worth recalling would be Sanchez and Shaham. I covered them in episode 413. Now, we already saw that Descartes admitted using arguments from these skeptics and from ancient authors like Cicero and Sextus Empiricus. The first of the meditations where these arguments are presented is itself something of a greatest hits compilation from the skeptical catalog.
Descartes semi-apologizes for this in a dedicatory letter that aimed to win approval for the work from the theology faculty at Paris, saying it is scarcely possible to provide any arguments which have not already been produced by someone else. So, one idea is that Descartes was not so much introducing the specter of radical doubt as reacting to the fact that others had already introduced it. There's some evidence for this interpretation.
In his replies to objections aimed at the meditations, Descartes pointed out that skepticism was vigorously alive in his own day, and asked, how can someone answer the skeptics who go beyond all the boundaries of doubt? How will he refute them? Still, I'm skeptical. Descartes makes no effort to persuade us that the scenarios he uses to induce doubt are compelling or even plausible.
In fact, he labels the most radical challenge to our knowledge, the evil demon hypothesis, as very slight and, so to speak, metaphysical. This doesn't exactly make it sound urgent to demon-proof our beliefs. To the contrary, the first meditation says that many of our uncertain beliefs are still reasonable to maintain. So why not tell the traditional skeptic, my beliefs may not be fully certain, but they are reasonable, which is good enough for me.
It would be one thing if I were convinced that I'm just as likely to be dreaming as not. Then I should suspend judgment, as Sexist Empiricus argued. But Descartes doesn't argue for this. Though I may be dreaming now or under the control of an evil demon, I have no reason to think so, and plenty of reason to think otherwise.
Another interpretation finds clues in Descartes' correspondence. As we just saw, the Descartes of the rules is happy to rest science upon intuition, on ideas we feel just cannot be false. But then Descartes came to reflect on divine omnipotence and decided that there are absolutely no limits on what God can do.
He told Mohsen in a letter that even mathematical truths are freely laid down by God, like the laws of physics. So if God wanted, for instance, to make the radii of a circle unequal, he could do so. Perhaps then Descartes' project in the meditations is to rule this out. He finds a truth not even God could falsify, namely that when I am doubting or thinking, I must exist, and then goes on to prove that God is not a deceiver and can be trusted not to make necessary truths suddenly turn false.
But here again, I'm doubtful that this is at the top of Descartes' agenda, not least because the Meditations doesn't even mention the issue of God's power over eternal truths. It's important that God is no deceiver, but not for this reason. Let's try something else, then. Maybe Descartes just thinks it is never acceptable to believe anything about which you are uncertain.
Well, not never. He speaks elsewhere of what he calls moral certainty, by which he means certainty that suffices for the conduct of our life, but is not absolute. In everyday life, you just have to go around acting as if things that seem very reasonable are true. Maybe you can't 100% prove that an almond croissant has just been handed to you because maybe you are being fooled by an evil demon, but you're going to bite into it nonetheless. Or if you don't want it, just let me know.
Moral certainty is enough for action, then. But is it enough for belief? Arguably not. For Descartes, we believe something when our will is sufficiently moved to accept it. If we realize that a given proposition might be false, however remote that possibility, would we really believe it?
We might be convinced that the proposition is probably true, but not that it is true. Descartes also notes that error comes from believing too indiscriminately. This should encourage us to become extra careful in our believing. Hence the vivid metaphors Descartes uses for his method of doubt, like raising a house to the ground and then building a new one on solid foundations. Or emptying out a whole barrel of apples to pick out the bad ones.
This gets us closer to understanding Descartes' project, but I think we're still not quite there. Think again about that idea of merely moral certainty, which is good enough for everyday life. when would we want to impose stricter criteria? There might be special cases even in our practical affairs. If your life literally depends on getting an answer right, you would perhaps hold out for absolute certainty. But that doesn't seem to be Descartes' concern.
Rather, what is contrasted to everyday life is philosophy and science. Here, Descartes is for once a true heir of the Aristotelians. Aristotle and his followers insisted that true philosophical or scientific understanding must be certain, which it achieves by dealing only with necessary truth. Remember the so-called Berul Affair? Descartes criticized his opponent for using merely probable ideas in a scientific context.
Cartesian philosophy and science will not be like this. It will not contain the occasional bad apple, will not be a house with a few cracks in the foundation. Actually, scholastics and common-sense civilians alike are not just suffering from the occasional false belief. Their whole understanding of the world is riddled with falsehood.
They believe in the reality of things like colors and sounds, cold and heat, little souls and rocks, a sun that goes around the earth. Somehow, Descartes needs to get his reader to give all this up. The science whose foundations are being laid in the meditations is radically counterintuitive and novel.
To get us from our current ignorance to accepting Cartesian science, we need a kind of therapy that teaches us to doubt everything we think we know. Above all, we must be led to suspect our sense experiences. Picard says this a few times, including in the preface, where he comments that the purpose of the doubting strategy 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.
And led toward what exactly? Two things that are not available to the senses, namely the soul and God. Their existence is more certain even than mathematical truths, because unlike mathematical truths, belief in the soul and in God is immune to doubt. Try as they might, the skeptics will never come up with a scenario that casts doubt on their existence, not even doubt of a slight and metaphysical sort. That makes the soul and God the right foundations to use for the rest of Cartesian science.
Which brings us finally to the Kogito. Like many of the best philosophical ideas, it's pretty simple, yet has far-reaching implications. Some of these will emerge next time when we look at Descartes' dualism. But here's the simple part. I cannot be wrong when I think I exist, because to be wrong about anything, I need to exist.
The reason I put it this way, instead of in the terms of the famous phrase, I think, therefore I am, is because it is how Descartes seems to understand the cogito in the second meditation. He introduces it in response to the evil demon hypothesis, the worry that there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving.
It doesn't matter how powerful or cunning the deceiver is. It could never trick me into thinking that I exist when I don't. How could I be tricked if I don't even exist? Now we can see why the cogito is for Descartes even more certain than mathematical truths, like 2 plus 3 equals 5.
We can imagine that an evil demon is inducing that belief in me, but there's no skeptical scenario that could undermine my conviction that I exist. My existence is literally indubitable, because my existence is a condition for doubting. Despite the therefore in I think therefore I am, Descartes insists that the cogito is not syllogistic in form. He is not inviting us to go through a mental operation along the following lines. Everything that thinks must exist, I think, therefore I exist.
And for good reason. That first premise, everything that thinks must exist, looks like a claim that would need defense and could be subjected to doubt. Rather, when I grasp that I must exist if I think or doubt, I do so via direct intuition, to use the terminology of his earlier rules for the direction of the mind. Thus, my own existence fulfills all the criteria Descartes demands for his principles. But this looks like a rather small stone on which to build the whole edifice of science.
In fact, the cogito provides even less than it may seem to do, because as Stigart is aware, it only shows that I exist at the moment that I am thinking or doubting. Thus his phrasing in the meditations, this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind. I cannot then use the cogito to prove that I existed five minutes ago, still less that I will continue to exist five minutes from now.
But here's one further thing we can add. Suppose I'm seeing a giraffe. Maybe I'm dreaming, or an evil demon is making me believe that there's a giraffe in front of me, so who knows whether there really is a giraffe. Still, I am sure that I seem to be seeing a giraffe, and for the same reason that my own existence is indubitable. For me to doubt whether I really am seeing a giraffe, I must first be under the impression that I am seeing a giraffe. So that's a bit more progress, but only a bit.
It falls far short of what Descartes needs, which is to eliminate the possibility of a superhuman deceiver. And this is where God comes in. Descartes needs to prove that God exists and is good, and he needs these proofs to be as certain as the upshot of the cogito.
He gives a couple of arguments to achieve this. The second one is a reworking of the ontological argument, familiar from the medieval philosopher Anselm. You can revisit episode 205 if you want, since it was devoted entirely to that argument. The first one is more original. Descartes says that, inspecting his own ideas, he finds that one of them is the notion of a perfect being. This idea is, he claims, clear and distinct, so in that respect it satisfies his usual demands for a principle.
but my having a clear and distinct idea of something doesn't guarantee that it exists. We saw that the idea of a triangle is clear and distinct, but who says that there have to be triangles in reality? The idea of God, though, is different. It cannot have come from Descartes' own mind, because the idea surpasses his mind in what Descartes calls objective reality, by which he seems to mean the degree of perfection involved in the idea.
Where then did the idea come from? It must be from a cause that has just as much perfection as the idea itself, which would only be a perfect being who really exists outside my mind. Picard is convinced that this argument is just as compelling as the cogito. The key premise that the idea would need a cause, at least as perfect as the content of the idea, seems obvious to him by the natural light of reason, another bit of terminology that already appeared in the rule.
As we'll see in a later episode, though, the first readers of the meditations did doubt the principle, and thus the whole argument. For now, we just need to understand how God functions in Descartes' overall strategy. Since God is a perfect being, we can rely on him not to be deceiving us systematically or allowing any other supernatural power deceive us. This allows us to banish the evil demon hypothesis.
Other skeptical scenarios do remain on the table. For instance, I could still be dreaming at any given moment. But the meditator now feels able to rely on his clear and distinct ideas. Whenever he is fixing mental vision continually on the same thing so as to keep perceiving it clearly, he can recognize clear and distinct ideas as true.
A good example would be mathematical truths. Such ideas are not intrinsically certain, like his own existence or God's existence, which are immune even to the evil demon hypothesis. but once we have God in the picture, we can rely on him to ensure that our clear and distinct ideas are also reliable.
So, now we can bring back in all the principles that Descartes was talking about in the rules. The deliverances of intuition and analysis would provide an adequate basis for science. Mission accomplished. Or is it? A lot of questions remain, including several about these clear and distinct ideas. Though they seem certain to Descartes, he admits that many such ideas are discovered only after lengthy investigations.
This is shown by some of the ideas we've already mentioned. The idea of a proportional mean between two numbers may be clear and distinct, but it's not going to occur to anyone who hasn't studied math. Then there's the problem that what seems clear and distinct may not be. Aristotelians would surely think the idea of coldness is as clear and distinct as it gets, but Descartes disagrees. So there's still work to do to sort bad apples from good ones.
One might also ask where clear and distinct ideas come from, presumably not from sensation, given that Descartes is so wary of trusting whatever it tells us. Actually, we already know the answer, at least in one case. The clear and distinct idea of God is given to us by God himself. and that seems to apply to all such ideas. God creates us such that the ideas are innate within us, though it is possible to go through life without noticing them.
Descartes saw it as his mission to bring the ideas to the full attention of his contemporaries. My principal aim has always been to draw attention to certain very simple truths which are innate in our minds, so that as soon as they are pointed out to others, they will not consider that they were ever ignorant of them. The notion that true ideas are inborn and need to be rediscovered through philosophical inquiry goes all the way back to Plato.
Descartes acknowledges this by citing the Mino, the platonic dialogue that introduces the theory of recollection. Now, in early modern philosophy, innatism is going to experience a rebirth, thanks largely to Descartes. But for my money, the most profound legacy of the meditations is a different one, one that would have horrified Descartes.
With this work, Descartes unwittingly gave a massive boost to skepticism. Unfortunately, his proofs of God seem to be the weakest link in his argumentative chain, and on his own telling, almost none of our beliefs are certain without a proof of God.
In Descartes' replies to objections aimed at the meditations, he notes that an atheist cannot be certain about anything apart perhaps from their own existence. Atheists cannot rule out the evil demon hypothesis, so they should doubt even mathematical truth. Many of us will find that consequence absurd, but it doesn't worry Descartes. What should have worried him, though, is that he risked putting everyone in the position of this hypothetical atheist, forced to doubt pretty much everything.
Ultimately, the skeptical arguments at the beginning of the meditations have struck readers as considerably more successful than the attempt to rebuild knowledge from the ground up. As David Hume observed, Cartesian doubt, were it ever possible to be attained by any human creature, as it plainly is not, would be incurable, and no reasoning could ever bring us to a state of assurance on any subject.
As an empiricist, Hume would have advised Descartes to get up from his chair, go out into the street, and use his sense experience as much as possible, since it is our senses and not God that are the source for all our ideas. As I've said, we should not overlook Descartes' own devotion to empirical investigation, but, as I've also said, he is distrustful of the senses, writing in the meditations that our erroneous beliefs stem precisely from the combination of our rational souls with our bodies.
And it's that combination we'll be exploring next time, as we turn to yet another famous aspect of Descartes' philosophy, one that has become more or less synonymous with Cartesianism, mind-body dualism. I hope you won't be of two minds whether to join me for that here on the History of Philosophy with