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 Munich. Online at historyofphilosophy.net. Today's episode, Ghost in the Machine, Cartesian Dualism. If you ask a modern-day philosopher to explain Cartesian dualism, they'll tell you it is a theory about the mind.
The Cartesian, impressed by the uniqueness of consciousness, postulates a mind, self, or soul that is a substance in its own right, and might be able to survive bodily death. But if you use your thinking self to consider it for about five seconds, you'll see that this cannot have been the radical new claim made by Descartes for the simple reason that people had been saying it for about 2,000 years before he came along.
Obviously, Plato and all those who thought of themselves as Platonists were dualists in this sense, but even Aristotle argues that the mind needs no bodily organ. This had inspired Aristotelians from late antiquity to the Renaissance to argue that he, too, made the rational part of the soul independent from the body.
The standard scholastic view, which Descartes would have learned well as a student, was that the soul is the substantial form of the body, responsible for all the body's vital powers, from digestion and sensation to imagination and memory. but also giving humans a capacity for abstract thought, which is carried out immaterially.
Insofar as the scholastics perceived any serious threat to this orthodoxy, it came from a non-dualist direction. Some schoolmen down in Padua had been flirting with the idea that the soul is so closely tied to the body that it cannot survive on its own. So, Descartes' innovation cannot have been that he postulated a separate rational soul. Rather, his decisive intervention was on the side of the body, or matter. His bold new physics would explain a wide range of phenomena mechanistically.
We've seen how he wanted to do that with things like celestial motion and the radiation of light, but he also wanted to extend this research program to the vital functions of plants, animals, and humans. Life, digestion, sensation, imagination, all of these can be explained in purely material terms. In short, Descartes' distinctive move was not to postulate a separable thinking soul. His scholastic opponents already accepted that.
It was to take the other functions of life away from the soul, giving them to matter. This left nothing for the soul to do but think. Descartes' contemporaries found this somewhat baffling. One of his sternest and most insightful critics, Pierre Gassendi, told him, I must admit that I had been laboring under a misapprehension.
I thought that I was addressing a human soul, or the internal principle by which a man lives, has sensations, moves around, and understands. Instead, I find I was addressing a mind alone. Even the more sympathetic Nelson was puzzled as to what Descartes meant by the word thinking. He assumed that Descartes must be talking about only abstract scientific thinking, which is what scholastics would mean by the term.
Descartes cleared up this misapprehension when he offered the following definition of thought. I use this term to include everything that is within us in such a way that we are immediately aware of it. Thus all the operations of the will, the intellect, the imagination, and the senses are thought. But this only deepens the confusion. Didn't we just say that for Descartes, sensation and imagination are bodily processes?
Yes and no. On the one hand, he thinks that he can explain the physical processes related to sensation and imagination in purely mechanical terms. When we see, for instance, light corpuscles strike the retina in the eye, and this causes a motion in the nerves, which are connected to the pineal gland in the center of the brain. This is where sensation and imagination are seated.
Images are thus formed in the brain, and Descartes was even willing to call these images ideas, writing, I wish to apply the term idea, generally, to all the impressions which the spirits are able to receive as they issue from the pineal gland. On the other hand it is the mind or rational soul that as it were takes notice of these physical processes that are happening in the brain and elsewhere in the body.
Thus, Descartes is also willing to say, it is the soul that sees and not the eye, and it sees immediately only through the intervention of the brain. So we have an incorporeal mind monitoring corporeal processes, and that monitoring is part of what Descartes means by thinking. On the other hand, Descartes also speaks of pure thought, which he defines as an understanding that is not concerned with any physical images.
In such a case, there's apparently thinking with no connection to anything happening in the body. But even when we are thinking, by being aware of sense experience, imagination, or memory, the thinking as such is an immaterial activity. How does Descartes know this? One answer is the increasingly familiar and increasingly frustrating appeal to clear and distinct ideas. Descartes finds it obvious that mental processes are not the kind of thing that could be physically realized.
The notion that we have of the mind is just entirely different from the notion we have of the body. Of course, this isn't going to satisfy anyone, but Descartes also thinks that he can infer dualism from the cogito argument. As we saw last time, the existence of the self is special, because unlike almost anything else, it is immune to doubt.
I am able to have absolute certainty about my own self while being in doubt as to whether my body is just the figment of a dream or a delusion caused by an evil demon. How then could the self be the same as the body? What then am I? asks Descartes, and immediately answers, a thing that thinks. What is that? A thing that doubts, understands, affirms, denies, is willing, is unwilling, and also imagines and has sensory perceptions.
So the Cogito argument is doing a lot of work for Descartes. It provides both the initial escape from radical doubt and an initial reason to accept dualism. But is his argument convincing? Already at the time, critics raised the following problem. Let's grant Descartes that he is certain that his mind exists, but is not certain that his body exists. Does this really show that his mind and body are different?
Consider the following analogy. Suppose I know that Superman has x-ray vision, but I don't know that Clark Kent has x-ray vision, because I don't know that Clark Kent is Superman. Obviously, this doesn't show that Clark Kent and Superman are not the same person. which allows us to see right through Descartes' argument. Perhaps his mind is just part of his body, like his brain.
So when he is certain that his mind exists, he's actually certain that his brain exists. He just doesn't realize it because he doesn't know that his mind is his brain. Or more likely, it is what Descartes would call a mode of his brain, a property or activity that belongs to it. Is there any way Descartes could escape from the objection? Yes, but not without making a few contentious metaphysical assumptions.
For Descartes, the mind is not a substantial form, which combines together with matter to produce the living human being. Instead, the mind just is a substance, as is the body. This means that both mind and body can exist on their own. To be a substance is to be independent, needing nothing else in order to exist, which, by the way, was also a test Aristotle used to tell whether something is a substance or not.
Descartes is careful here, though. The fact that the mind can exist on its own didn't mean that it does. Perhaps God has set things up so that minds only ever exist together with bodies. But, speaking of God, Descartes observes that divine omnipotence at least could bring it about that the mind exists without matter, or vice versa. The reason we know he could do this is that both mind and matter have what Descartes calls principal attributes.
The principal attribute of body is that it is extended, or rather it just is extension. As for mind, its principal attribute is thinking, as we can see from the way we can come to grasp its existence in the cogita argument, I think, therefore I am. These two ideas, extension and thinking, have nothing to do with one another. In fact, they even seem to be incompatible. The thinking mind is indivisible, there's no such thing as half a mind, whereas every extension can be divided.
But that isn't Descartes' main point. His main point is that we grasp body and mind as being independent substances because they have clearly distinct natures. This would not apply to Superman and Clark Kent, who are not differentiated by substantial attributes. Superman could just be Clark Kent without glasses and with superpowers. In fact, that's exactly what he turns out to be.
In a famous passage from The Meditations, Descartes shows us how to perform this kind of conceptual test, which we saw him calling analysis in the previous episode. He describes picking up a piece of wax. It has various features, like hardness, shape, color, and scent. Then he brings it close to the fire and sees it lose all these features as it melts. It remains something extended, flexible, and changeable, features that belong to it just insofar as it is matter or body.
Since this underlying nature is nothing that is evident to the senses, it must be grasped directly by the mind. So, the wax example gives us an illustration of both attributes, the extension of matter, and the thinking, or pure understanding, of the mind, which gets past sensation and imagination to grasp extension.
Other famous passages in the meditations make related points about pure understanding as opposed to sensation. Right after the wax passage, Descartes mentions another case where the mind has to infer something or make a judgment that is not given to sensation. We might look out the window and think we see people walking in the street below, but actually we only see their hats and coats and have to add a mental judgment that there must be humans wearing them.
That's like grasping the extension that underlies the sensible qualities of the wax. In other cases, we might think of something that is completely inaccessible to sensation or imagination. While we can imagine simple figures like a triangle or square, what about a chiliagon, which is a figure with 1,000 sides? I'm guessing not even Superman could picture that, but it's no trouble to understand the idea in pure thought.
With all these arguments and examples, Descartes has managed to isolate the mind as nothing but a thinking subject. This is more or less what we mean when we talk about mind today, thanks in no small part to Descartes, which is why I have been using this word throughout the episode. But Descartes also regularly calls it the soul, or rational soul.
This amounts to applying the word soul very differently than the scholastics had. As one modern-day scholar has put it, Descartes was the first to claim that the soul is not the principle of life. But this is bound to create a problem for him because matter is not alive either. To quote another scholar, Cartesian matter, being no more than extension, is utterly inert. Genuine agency pertains to spiritual substances alone.
Somehow, Descartes is going to have to explain all those functions carried out by the Aristotelian soul, using no explanatory resources apart from extended corpuscles and motion. How is he going to manage this? The short answer is that he isn't, but not for lack of trying. Obviously, contemporary physiological theories and his own observations were going to fall well short of providing accurate, fully mechanistic explanations of things like the nervous system or reproductive organs.
to say nothing of psychological phenomena like memory and the imagination. But such explanations are exactly what he was after, as we can see from his telling Marcin that one goal of his activities in animal dissection was to explain what imagination, memory, etc. consist in. It's routine to point out that Descartes was inspired by technological advances in his day. For instance, the moving statues operated by water pressure that he saw as a young man at Royal Gardens in the outskirts of Paris.
Indeed, Descartes frequently compares biological phenomena to clocks and God to a clockmaker. But Aristotle had also compared animal motion to the motion of automated toys, so the idea was not entirely new. I suspect that technological examples were not, as it were, the driving engine of Descartes' approach to science, but only encouraged him to pursue the mathematics-inspired physics he discussed early on with Isaac Baikman.
This orientation meant that Descartes welcomed such developments as William Harvey's discovery of the circulation of the blood. However, he disagreed about the cause. For him, the heart was not pumping the blood around the body, but rather expanding when the blood inside is heated, in a process he compared to fermentation. As for the nervous system, he believes that nerves are hollow and allow for the passage of animal spirit, which is like a fine wind or flame.
This spirit is a holdover from the Galenic medical tradition. In Greek, it was called pneuma, as in pneumatic. It is refined out of the blood coming from the heart and then conveyed from the brain to the rest of the body in a process Descartes compares to playing a church organ. Animal spirit is responsible for a wide variety of vital functions. Take reflex motion.
Using the example of pulling one's foot away from a hot fire before it gets burnt, Descartes suggests that the animal spirit connects the foot to the brain, like a string that gets pulled at one end and rings a bell at the other end. Or, take another example, memory of earlier sense experience. Descartes thinks this involves the flowing of spirit through channels in the brain that were used before.
He compares the process to the crease in a paper that has been folded before and to holes in a cloth that have been punched through it by needles. Even sneezing is caused by leakage of animal spirit from the brain into the nose. Notice that for all the talk of machines, Descartes is not thinking of the body as if it were made of gears and levers.
As he knew well from his dissections, what you'll find if you cut open an animal or a human is a sopping wet mess. His physiology duly evokes hydraulics, with fermenting concoctions and spirits flowing along channels. Notice also that Descartes is being true to his methodological principles, using comparisons to draw the mind toward underlying principles and structures.
When explaining light, he talked of bouncing tennis balls. When explaining the body, he talks of church organs, folded paper, and strings attached to bells. The analogies make it easy to imagine what might be happening inside the body, and to make it even easier, he sketched diagrams for inclusion in his printed work. He told Nassim that these would need improvement from the engravers, Descartes himself not being much of an artist.
These diagrams were an important part of the Cartesian scientific project, not unlike the blueprint of a machine or even a drawing used in a geometrical pre. Indeed, in the diagrams, he often labels parts of the body, like the foot or pineal gland, with letters, as one would do in such a proof. From our point of view, this might seem to create a spurious impression of scientific exactness.
For all the diagrams and systematicity, for all the anatomical dissections, Descartes was largely just making up plausible stories about what might be going on. These stories turned out to be false pretty well across the board, in part precisely because they appealed to fairly simple mechanical processes. In some cases, he even rejected the correct physical explanation in favor of an incorrect one as when he tried to improve on Harvey's account of blood circulation.
Still, a sympathetic observer might give him credit for the general approach, if not the detailed result. One such observer was Nicholas Steno, a Danish scientist who praised Descartes when lecturing on the brain in 1665. This glowing passage deserves quotation at length. Descartes was the first who dared to explain all the functions of man, and especially of the brain, in a mechanical fashion.
Other authors describe man. Descartes puts before us merely a machine, but by means of this, he very clearly exposed the ignorance of others who have treated up man and opened up for us a way by which to investigate the use of other parts of the human body. with the same clarity he shows us in the parts of his man-machine, which no one before him attempted.
It is therefore necessary not to condemn Descartes if his account of the brain is not found entirely conformable to experience. The excellence of his genius, which appears principally in the treatise on man, covers the errors of his hypotheses. which seems like a fair assessment, though I would suggest at least one amendment. Steno here speaks of a man-machine and of investigation into the human body, which is true, but only half the story.
Remember, Descartes told Messon he was visiting butcher shops nearly every day to see bodies being slaughtered. And though the 16th century was a violent time, I'm pretty sure those were not the bodies of humans. Everything he says about human bodies is meant to apply equally to the bodies of higher animals, since they also have very similar organs—brains, nervous systems, hearts, blood, and so on.
which is not to deny that Descartes' ultimate aim was to understand the human body. In fact, he once said, the preservation of health has always been the principal end of my studies, meaning, of course, the health of humans, not animals. On the other hand, Descartes owned a dog named Monsieur Grat, and we may hope that he wished this dog good health too.
Equally, we might worry that he didn't, because one of Descartes' most notorious philosophical positions concerns the inner life of animals, to wit, that they don't have one. This takes us back to sensation and imagination. Descartes separates the physical change in the body from the awareness of that change. For instance, when light particles hit the retina and cause a motion in the optic nerve, that enables us to see. But as I quoted him saying, it is the soul that sees and not the eye.
Animals do not have souls or minds, so only the material side of this story applies to them. Which sounds kind of crazy. Is Descartes really trying to convince us that animals can't see? Well, it depends what you mean by seeing. Their visual organs are affected by the environment, and this sets off further motions in their body. In Arnaud's reply to the meditations, he recalls an example originally found in Avicenna. What happens when a sheep sees a wolf and runs away in fear?
Descartes answers that he finds nothing surprising in the notion that light reflected from the body of a wolf onto the eyes of a sheep can arouse the movements of flight in the sheep. No thinking or mental awareness need be involved. Descartes thus compares the sense experiences of animals to the ones we have when our mind is on something else, or to the sensations that people would have when sleepwalking.
The animals themselves are, of course, compared to machines Swallows are like clocks when they return in spring, and we can tell from the instinctive, routinized, and sometimes pointless actions of animals that they are like mechanized functions. Trains flying in a standard pattern, or dogs and cats scratching at the ground to bury their excrement, even when the ground is too hard to dig. The inflexibility shown by animal behavior is one of Descartes' primary arguments for their mindlessness.
His other argument is an appeal to language. As he says in Discourse on the Method, even very stupid humans are capable of expressing themselves using language, something we do not observe in animals. Animals do make noises of various kinds, of course, but this is only a matter of communicating what Descartes calls their natural impulses of anger, fear, hunger, and so on.
This applies to birds that can use human language, like a magpie that greets its owner when she comes into the room, which is only an automatic noise caused by a physical process. As that example shows, Descartes' language argument is in fact closely related to the first point, that animal behavior seems to be automatic, and hence unintelligent.
Humans can react to changing circumstances in a highly adaptable and versatile fashion, and their language use is a prime example, because language is itself infinitely flexible and can be used to represent any idea that comes to mind. Descartes was convinced that no machine could ever be capable of this, and animals are, in the end, nothing but machines.
Thanks to these views, Descartes is often held up as the ultimate example of philosophical dismissiveness toward animals. And not without good reason. He told Moussen that when animals are harmed, they have no awareness of pain. No wonder he had no compunctions about engaging in vivisection, meaning the anatomical dissection of living animals, as part of his scientific investigation.
We're liable to be appalled by all this and to think it was really Descartes who was insensitive and unfeeling, not the animals. But there are some things we can say in mitigation. Descartes' animals may be machines, but they are machines designed by God with utmost subtlety, vastly more sophisticated than clocks or other man-made devices. In keeping with this, Descartes is happy to use functional language when speaking of animal bodies, as if their organs and limbs have a purpose.
Of course, he does not accept the natural teleology and final ends assumed by Aristotelian philosophers, but animal bodies reveal the design of God, who is like the ultimate clockmaker. As a result, animals have a high degree of what Descartes calls objective reality, a concept we saw him using in his proof of God's existence in the meditations.
In other words, our ideas of animals involve perfection and coherence, in contrast to the incoherently assembled animals of myth, like the chimera, which is made of parts of a serpent, lion, and goat. So animals may not have minds, but they do display a profoundly impressive functional unity. While this is perhaps not going to serve as the basis for our satisfying animal ethics, it would at least imply that we should show respect to animals as products of a divine creator.
And finally, it is to Descartes' credit that he admitted uncertainty about all of this. He wrote in one letter that, to be really sure that animals have no minds, we would have to reach into their hearts with our own minds, which is obviously impossible. All this leaves us with at least one final puzzle. How exactly is it that our minds reach into our own hearts? Given that the mind and the body are substances of entirely different natures, how can they interact?
So far, I've been talking as if a disembodied mind somehow observes what's going on in the body as if we're watching a movie from the very back row of a cinema. But as Descartes admits in the Meditations, this cannot be right. Unlike animals, when we are harmed, we do feel pain, an experience that points towards an intimate connection between body and mind.
So alluding to an analogy already found in Aristotle, Descartes says that the mind is not in the body like a sailor riding in a ship, but is instead intermingled with the body. Given everything he's told us about the metaphysics of matter in mind, this is hard to understand. It's as if one were preparing batter for a cake and told to mix in the number four.
Still today, the metaphysical gap between mind and body is a central challenge for Cartesian dualism, and it did not take centuries for people to notice the problem. Among those who pressed Descartes on the issue was Elizabeth of Bohemia, the most important philosophical interlocutor of his later years. We'll be getting to their correspondence soon, but first I want to turn to an interlocutor of my own.
Now that we've surveyed the main themes of the meditations, his skeptical method, the cogito, proof of God, and mind-body dualism, it seems like the right time to ask an expert what we should make of the work as a whole. And that's what we'll be doing next time here on The History of Philosophy.