Descartes: The beginnings of modern philosophy of mind

The dominant view of the mind for the last three hundred years of Western philosophy has been one that derives from the French philosopher Rene Descartes, one of the most influential philoso­phers of all time.

Descartes' best-known work, the Discourse on Method—its full title is actually Discourse on the Method for Properly Conducting Reason and Searching for Truth in the Sciences—is written in a clear, attractive style. This may make what he is saying seem simpler and more obvious than it really is, so we need to consider what he says very carefully. Here is a passage from the fourth part of the Discourse, published in 1637, where he sets out very clearly his view of the nature of his own self:

This passage contains practically every central component of Descartes' philosophy of mind.

First, Descartes is a dualist.

Second, what he thinks you really are, your self, is a mind. Since you are your mind, and minds are totally independent of bodies, you could still exist, even without a body.

Third, your mind and your thoughts are the things you know best. For Descartes it is possible, at least in principle, for there to be a mind without a body, unable, however hard it tries, to become aware of anything else, including any other minds. Descartes knew, of course, that the way we do in fact come to know what is happen­ing in other minds is by observing the speech and actions of “other bodies.” But for him there were two serious possibilities, each of which would mean that our belief in the existence of other minds was mistaken. One is that these other bodies could be mere fig­ments of our imagination. The other is that, even if bodies and other material things do exist, the evidence we normally think justifies our belief that other bodies are inhabited by minds could have been produced by automata, by mindless machines.

Fourth, the essence of a mind is to have thoughts, and by “thoughts” Descartes means anything that you are aware of in your mind when you are conscious. (The essence of a kind of thing, K, is the property—or set of properties—whose possession is a necessary and sufficient condition for membership in K. That is, if some­thing has the essential property E, then it belongs to K—so E is suffi­cient for membership in K; anything that doesn't have E doesn't belong to K—so E is necessary for membership.) In other places Descartes says that the essence of a material thing—the property, in other words, every material thing must have—is that it occupies space. This means that for Descartes the two essential differences between material things and minds are (1) that minds think, whereas matter does not, and (2) that material things take up space, whereas minds do not.

It is not surprising that Descartes believed that matter does not think. Very few people suppose that stones or tables or atoms have thoughts. But why did he think that minds were not in space? After all, you might think that my mind is where my body is. But if I had no body, as Descartes thought was possible, I would still have a mind. So he couldn't say that a mind must be where its body is, sim­ply because it might not have a body at all. Still, if I do have a body, why shouldn't I say that that is where my mind is? If I didn't have a body, that would be the wrong answer; but, as it happens, I do.

I think the main reason for thinking that minds are not in space is that it does really seem strange to ask, “Where are your thoughts?” Even if you answered this question by saying “In my head,” it would not be obvious that this was literally true. For if they were in your head, you could find out where they were in your head, and how large a volume of space they occupied. But you cannot say how many inches long a particular thought is, or how many centimeters wide, or whether it is currently north or south of your cerebral cortex.

There is a fifth and final characteristic of this passage that is typ­ical of Descartes' philosophy of mind: throughout the argument Descartes insists on beginning with what can be known for certain, what cannot be doubted. He insists, that is, on beginning with an epistemological point of view.

These are the major features of Descartes' philosophy of mind, and, as I said, this has been the dominant view since his time. So dominant has it been, in fact, that by the mid-twentieth century the central problems of the philosophy of mind were reduced, in effect, to two.

Now, it is just this dualism that raises some of the major difficul­ties of Descartes' position. For anyone who thinks of mind and body as totally distinct needs to offer an answer to two main questions. First, how do mental events cause physical events? How, for exam­ple, do our intentions, which are mental, lead to action, which involves physical movements of our bodies? Second, how do physi­cal events cause mental ones? How, for example, is it possible for physical interaction between our eyes and the light to lead to the sensory experiences of vision, which is mental? And, as we shall see, the answer Descartes gives to these questions seems not to be con­sistent with his explanation of the essential difference between body and mind.

Descartes' answer to these questions seems clear and simple enough. The human brain, he thought, was a point of interaction between mind and matter. Indeed, Descartes suggested that the pineal gland, in the center of your head, was the channel between the two distinct realms of mind and matter. That was his answer to the mind-body question.

But this theory comes into conflict with Descartes' claim that what distinguishes the mental from the material is that it is not spatial. For if mental happenings cause happenings in the brain, then doesn't that mean that mental events occur in the brain? How can something cause a happening in the brain unless it is another happening in (or near) the brain? Normally, when one event—call it “A”—causes another event—call it “B”—A and B have to be next to each other, or there has to be a chain of events that are next to each other which runs from A to B.

Descartes wants to say that thoughts aren't anywhere. But, according to him, at least some of the effects of my thoughts are in my brain, and none of the direct effects of my thoughts are in any­body else's brain. My thoughts regularly lead to my actions and never lead directly to someone else's. We have now reached one central problem for Descartes' position. For it is normal to think that things are where their effects originate. (We can call this the causal account of location.) And on this view my thoughts are in my brain, which is the origin of my behavior. But if mental events occur in the brain, then, since the brain is in space, at least some mental events are in space also. And then Descartes' way of distin­guishing the mental and the material won't work. Let's call this apparent conflict between

a)     the fact that mind and matter do seem to interact causally and

b) Descartes' claim that the mind is not in space

Descartes' problem. Once you accept the causal account of loca­tion, there are four main ways you might try to deal with this problem.

The first would be to deny that causes and their effects have to be in space. Descartes' is only one of the possible dualist solutions to the mind-body question that takes this approach.

A second way out of Descartes' problem is to deny that there are any causal connections between mind and matter at all. On this view there are corresponding material and mental realms, which run in parallel, without any causal interaction. Psychophysical parallelism, as this theory is called, certainly escapes Descartes' problem. But we are left with a mystery: why do the mind and the body work together if there is no interaction between them? Psychophysical parallelism says mind and body run in parallel without explaining why.

The third way out of Descartes' problem would be to try a dif­ferent way of distinguishing mind and matter. If you think that both causes and their effects have to be in space and that mental events have material causes or effects, you cannot maintain Descartes' claim that minds are not spatial. Starting with some new way of dis­tinguishing mind and matter, however, you might still be able to keep dualism, while taking into account the fact that causes have to be in space if their effects are.

But however you distinguish the mental and the material, if you believe they are two different kinds of thing you will have to face the other-minds problem. If your mind and body are utterly distinct kinds of thing, how can I know anything about your mind, since all I can see (or hear or touch) is your body? You brush off the fly, and I judge that you want to get rid of it. But if there is no necessary con­nection between what your body does and what is going on in your mind, how is this judgment justified? How can I know your body isn't just an automaton, a machine that reacts mechanically, with no intervening mental processes? If you find this thought compelling, you might want to try a solution to Descartes' problem that is not dualist at all.

So the fourth and last way out of Descartes' problem is just to give up the idea that mind and matter really are distinct kinds of thing, and thus to become what philosophers call a “monist.” Monism is the view that reality consists of only one kind of thing. For monists, beliefs and earthquakes are just things in the world. Things in the world can interact causally with each other, so there's nothing surprising about my belief that there's a table in my way causing me to move the table. The movement of the table is partly caused by the belief. That's no more surprising than a movement of the table caused by an earthquake.

I've suggested that thinking about the other-minds problem might lead you to give up dualism. And if you consider the very evi­dent fact that we do know that other people have minds you may be led, with many twentieth-century philosophers and psychologists to the form of monism called “behaviorism.” Behaviorism, which we noticed as one possible response to the problem of deciding whether a computer could have a mind, is simply the identification of the mind with certain bodily dispositions. A behaviorist, then, is someone who believes that to have a mind is to be disposed to behave in certain ways in response to input. On one behaviorist view, for example, for English-speakers to believe that something is red is for them to be disposed to say, “It is red,” or to reply with a “Yes” if asked the question “Is it red?” And dispositions like this are a familiar part of the world. Being sharp is (roughly) being disposed to cut if pressed against a surface; being fragile is (roughly) being disposed to break if dropped.

There's a strong contrast between behaviorism and Descartes' view. Descartes thought belief was a private matter. That had two consequences. First, that you know for sure what you believe. Second, that only you know for sure what you believe. And the trou­ble with Descartes' view of the mind is that it makes it very hard to see how we can know about other minds at all. For the behaviorist, on the other hand, belief is a disposition to act in response to your environment. If you respond in the way that is appropriate for some­one with a certain belief, that's evidence that you have it. Since your response is public—visible and audible—others can find out what you believe. Indeed, as the English philosopher Gilbert Ryle argued in his book The Concept of Mind, we sometimes find out what we ourselves believe by noticing our own behavior.

It is a big step from saying that some of our mental states are things that other people can know about, to saying, with the behav­iorists, that all of them must be in this way public. Yet one of the most influential philosophical arguments of recent years has just this conclusion. The argument was made by the Austrian-born philoso­pher Ludwig Wittgenstein, whose work we will discuss again in the chapter on language.

Wittgenstein began by supposing that anyone who believed in the essentially private thoughts of Descartes' philosophy of mind would find it quite acceptable to suppose that someone could name a private experience—one, that is, that nobody else could know about. And indeed, as we shall see in Chapter 3, Thomas Hobbes, who was an English philosopher who reacted against some of Descartes' ideas, thought that we used words as names of our pri­vate thoughts in order to remember them. He called them “marks” of our thoughts. To use marks in this way, someone would have to have a rule that they should use the name just on the occasions where that private experience occurred. Wittgenstein argued that obeying such a rule required more than that there should be both circumstances when it was and circumstances when it wasn't appro­priate to use the name. He thought that it also required that it should be possible to check whether you were using the name in accordance with the rule. And he offered a very ingenious argu­ment that was supposed to show that such checking was impossible. If Wittgenstein was right, there could be no such “private lan­guages.” And his argument is called, for that reason, the private­language argument.

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