The aim of this book is to introduce the reader to the philosophy of mind. I have three objectives. First, the reader should get an understanding of the most important contemporary issues and discussions in this field, and also get some understanding of their historical background. Second, I want to make clear what I think is the correct way to approach these problems, and I even hope to provide answers to many of the questions I pose. And third, most important of all, I would like the reader to be able to think about these issues for himself or herself after reading the book. I can state all of these aims at once by saying that I am trying to write the book that I wish I had read when I first began to think about these questions. I write out of the conviction that the philosophy of mind is the most important subject in contemporary philosophy and that the standard views—dualism, materialism, behaviorism, functionalism, computationalism, eliminativism, epiphenomenalism—are false.
One agreeable feature of writing about the mind is that it is not necessary to explain why the subject is important. It takes a while to see that illocutionary acts and quantified modal logic are important subjects in philosophy, but everyone can see immediately that the mind is central to our life. The operation of the mind—conscious and unconscious, free and unfree, in perception, action, and thought, in feeling, emotions, reflection, and memory, and in all its other features—is not so much an aspect of our lives, but in a sense, it is our life.
There are risks in writing such a book: among the worst things we can do is to give readers the impression that they understand something they do not really understand, that something has been explained when it has not been explained, and that a problem has been solved when it has not been solved. I am acutely aware of all these risks, and in what follows I will be emphasizing areas of human ignorance—my own as well as others’—as much as areas of human understanding. I think that the philosophy of mind is so important that it is worth taking these risks. For a number of important historical reasons, the philosophy of mind has become the central topic in contemporary philosophy. For most of the twentieth century the philosophy of language was “first philosophy.” Other branches of philosophy were seen as derived from the philosophy of language and dependent on results in the philosophy of language for their solution. The center of attention has now moved from language to mind. Why? Well, first, I think many of us working in the philosophy of language see many of the questions of language as special cases of questions about the mind. Our use of language is an expression of our more biologically fundamental mental capacities, and we will not fully understand the functioning of language until we see how it is grounded in our mental abilities. A second reason is that with the growth of knowledge we have seen a movement away from treating the theory of knowledge, epistemology, as central in philosophy and we are now prepared to do a more substantive, theoretical, constructive philosophy, rather than just dealing piecemeal with specific traditional problems. The ideal place to begin that constructive philosophy is to start by examining the nature of the human mind. A third reason for the centrality of the mind is that, for many of us, myself included, the central question in philosophy at the beginning of the twenty-first century is how to give an account of ourselves as apparently conscious, mindful, free, rational, speaking, social, and political agents in a world that science tells us consists entirely of mindless, meaningless, physical particles. Who are we, and how do we fit into the rest of the world? How does the human reality relate to the rest of reality? One special form of this question is, What does it mean to be human? The answers to these questions have to begin with a discussion of the mind, because mental phenomena form the bridge by which we connect with the rest of the world. A fourth reason for the preeminence of the philosophy of mind has been the invention of “cognitive science,” a new discipline that attempts to go deeper into the nature of the mind than was customary in traditional empirical psychology. Cognitive science requires a foundation in the philosophy of mind. Finally, more controversially, I think the philosophy of language has reached a period of relative stagnation because of certain common mistakes that surround the doctrine of so-called externalism, the idea that the meanings of words, and by extension the contents of our minds, are not inside our heads, but are matters of causal relations between what is in our heads and the external world. This is not the place to rehearse those issues in detail, but the failures to give an account of language on an externalist premise have led to a fallow period in the philosophy of language; and the philosophy of mind has taken up the slack. I will say more about externalism in chapter 6.
The philosophy of mind has a special feature that distinguishes it from other branches of philosophy. In most philosophical subjects there is no sharp division between what the professionals believe and the opinions of the educated general public. But on the issues discussed in this book, there is an enormous difference between what most people believe and what the professional experts believe. I suppose most people in the Western world today accept some form of dualism. They believe they have both a mind, or a soul, and a body. I have even heard some people tell me they have three parts—a body, a mind, and a soul. But this is definitely not the view of the professionals in philosophy, psychology, cognitive science, neurobiology, or artificial intelligence. Almost without exception, the professional experts in the field accept some version of materialism. A great deal of effort in this book will be devoted to trying to explain these issues and solve the attendant problems.
Let us suppose then that the mind is now the central topic in philosophy and that other questions, such as the nature of language and meaning, the nature of society, and the nature of knowledge are all in one way or another special cases of the more general characteristics of the human mind, How should we proceed to examine the mind?
In philosophy there is no escaping history. Ideally, I sometimes think, I would just like to tell my students the truth about a question and send them home. But such a totally unhistorical approach tends to produce philosophical superficiality. We have to know how it came about historically that we have the questions we do and what sorts of answers our ancestors gave to these questions. The philosophy of mind in the modern era effectively begins with the work of René Descartes (1596-1650). Descartes was not the first person to hold views of the kind he did, but his view of the mind was the most influential of the so-called modern philosophers, the philosophers of the seventeenth century, and after. Many of his views are routinely expounded, and uncritically accepted today by people who cannot even pronounce his name. Descartes’ most famous doctrine is dualism, the idea that the world divides into two different kinds of substances or entities that can exist on their own. These are mental substances and physical substances. Descartes’ form of dualism is sometimes called “substance dualism.”1
Descartes thought that a substance has to have an essence or an essential trait that makes it the kind of substance that it is (all this jargon about substance and essence, by the way, comes from Aristotle). The essence of mind is consciousness, or as he called it “thinking”; and the essence of body is being extended in three dimensions in physical space, or as he called it “extension.” By saying that the essence of the mind is consciousness, Descartes is claiming that we are the sort of beings we are because we are conscious, and that we are always in some conscious state or other and would cease to exist if we ceased to be in some conscious state. For example, right now my mind is concentrating consciously on writing the first chapter of this book, but whatever changes I go through when I stop writing and, for example, start eating dinner, I will still continue to be in some conscious state or other. In saying that the essence of body is extension, Descartes is claiming that bodies have spatial dimensions: the desk in front of me, the planet Earth, and the car in the parking lot are all extended or spread out in space. In Descartes’ Latin terminology the distinction is between res cogitans and res extensa. (Descartes’ name, by the way is a contraction of “Des Cartes,” Latin: “Cartesius,” meaning of the cards; and the corresponding English adjective is “Cartesian”)
Cartesian dualism was important in the seventeenth century for a number of reasons, not the least of which being that it seemed to divide up the territory between science and religion. In the seventeenth century the new scientific discoveries seemed to pose a threat to traditional religion and there were terrific disputes about the apparent conflict between faith and reason. Descartes partly, although not entirely, defused this conflict by, in effect, giving the material world to the scientists and the mental world to the theologians. Minds were considered to be immortal souls and not a proper topic of scientific investigations, whereas bodies could be investigated by such sciences as biology, physics, and astronomy. Philosophy, by the way, he thought could study both mind and body.
According to Descartes, each essence has different modes or modifications in which it can occur. Bodies are infinitely divisible. That is, they can in principle be divided up indefinitely into smaller pieces, and in this sense each body can be destroyed, though matter in general cannot be destroyed. The amount of matter in the universe is constant. Minds, on the other hand, are indivisible, that is, they cannot be divided into smaller pieces, and thus they cannot be destroyed in the way that bodies can. Each mind is an immortal soul. Bodies, as physical entities, are determined by the laws of physics; but minds have free will. Each of us as a self is identical with his or her mind. As living human beings we are composite entities, comprising both a mind and a body, but for each of us the self, the object referred to by “I,” is a mind that is somehow attached to our body. Gilbert Ryle, a twentieth-century philosopher of mind, sneered at this aspect of Descartes’ view by calling it the doctrine of “the ghost in the machine.” Each of us is a ghost (our mind) inhabiting a machine (our body).2 We know both the existence and the contents of our minds by a kind of immediate awareness, which Descartes summarizes in the most famous sentence of his philosophy, “Cogito ergo sum”: I think therefore I exist. This looks like a formal argument with “I think” as premise and “I exist” as conclusion, but I believe that Descartes intended it also to record a kind of inner inspection of the existence and the contents of the mind. I cannot be mistaken about the existence of my own consciousness, hence I cannot be mistaken about my own existence, because it is my essence to be a conscious (that is, thinking) being, a mind. Nor can I be mistaken about the contents of my mind. If it seems to me, for example, that I have a pain, then I do have a pain.
Bodies, on the other hand, cannot be known directly but only indirectly by inferring their existence and features from the contents of the mind. I do not directly perceive the table in front of me; but, strictly speaking, I perceive only my conscious experience of the table, my “idea” of the table; and I infer the existence of the table from the presence of the idea. My present idea of the table is not caused by me, so I have to assume that it is caused by the table.
Descartes’ account of the relationship between mind and body can be summarized in the accompanying chart. In addition to having an essence each substance has a series of modifications or properties, and these are the particular forms that the essence takes.
| Substances | ||
| Mind | Body | |
| Essence | Thinking (consciousness) | Extension (having spatial dimensions) |
| Properties | Known directly Free Indivisible Indestructible | Known indirectly Determined Infinitely divisible Destructible |
Descartes’ views have led to endless debates and it is fair to say that he left us with more problems than solutions. The account that I just gave you, brief as it was, of reality as dividing into the mental and the physical, leaves us with a bushel of problems of which here are eight that most concerned Descartes himself and his immediate successors.
What exactly are the relations between the mental and the physical, and in particular how can there be causal relations between them? It seems impossible that there should be causal relations between two completely different metaphysical realms, the physical realm of extended material objects and the mental or spiritual realm of minds or souls. How does anything in the body cause anything in the mind? How does anything in the mind cause anything in the body? Yet, it seems we know that there are causal relations. We know that if somebody steps on my toe, I feel a pain even though his stepping on my toe is just a physical event in the physical world, and my feeling of pain is a mental event that occurs inside my soul. How can such things happen? Just as bad: it seems there are causal relations going the other way as well. I decide to raise my arm, an event that occurs inside my conscious soul, and, lo and behold, my arm goes up. How are we supposed to think that such a thing could ever happen? How can a decision in my soul cause a movement of a physical object in the world such as my body? This is the most famous problem that Descartes left us, and it is usually called the “mind-body problem.” How can there be causal relations between the two? Much of the philosophy of mind after Descartes is concerned with this problem, and it is still, in spite of all of our progress over the centuries, a leading problem in contemporary philosophy. I believe it has a fairly obvious general philosophical solution, which I shall explain later; but I have to tell you in advance that many—maybe most—of my colleagues are strongly in disagreement with my claim that we have a ready solution to Descartes’ problem.
There are really two sets of problems. How can anything physical produce an effect inside my soul, which is nonphysical, and how can events in my soul affect the physical world. In the past century and a half the first of these questions has been transformed in a way that Descartes would not have accepted. In its modern version, the question is, How can brain processes produce mental phenomena at all? How can brains cause minds? Descartes did not think such a thing was possible, because on his account minds have an existence completely independent of the brain. The problem for Descartes was not the general question of how a mental substance can arise out of neurobiology, because for him it cannot. His question was rather how specific mental contents such as feeling a pain can arise from the impact of an injury to my body. We think the very existence of a mind is explained by the operations of the brain. Descartes did not think that was possible. For him the question was only how specific thoughts and feelings, such as a sensation of pain, can be caused by events occurring to the body.
It is important to emphasize this point: we tend to think, even the dualists among us, that our bodies with their brains are conscious. Descartes did not think that. He thought bodies and brains could no more be conscious than tables or chairs or houses, or any other hunk of junk. Conscious souls are separate, though somehow attached to human bodies. But no material object, living or dead, is conscious.
I said that according to Descartes each of us is a mind and that each of us knows the contents of his or her mind directly, but how do I know that other people have minds? What makes me confident, when, for example, I meet you, that you have a mind? After all, all I can observe is your body, including its physical movements and the sounds that come out of its mouth that I interpret as words. But how do I know that there is anything behind all these physical phenomena? How do I know that you have a mind when the only mind that I have direct knowledge of is my own mind?
We might think that I can infer the existence of mental states in you by analogy with myself. Just as I observe in my own case a correlation between input stimulus, inner mental state, and output behavior; so in your case, because I can observe the input stimulus and the output behavior, I infer by analogy that you must have an inner mental state corresponding to mine. Thus, if I hit my thumb with a hammer, the input stimulus causes me to feel a pain, which in turn causes me to cry out. In your case, so the story goes, I observe the input stimulus and the crying out, and I simply plug in the gap by making an analogy between you and me.
This is a famous argument, called the “argument from analogy.” But it doesn’t work. In general, it is a requirement on inferential knowledge that if the knowledge claim is to be valid, there must be, in principle, some independent or noninferential way to check the inference. Thus, if I think that there is someone in the next room by inferring her presence from sounds that I hear, I can always go in the next room and check on this inference to see if there really is someone in the next room causing the sounds. But if I make an inference from your stimulus and your behavior to your mental state, how can I ever check the inference? How can I ever see that I am correctly inferring and not just making a wild guess? If I take it to be a kind of scientific hypothesis that we test by scientific methods, whether or not you have mental states corresponding to your observable stimulus and response patterns, in the same way that I have mental states corresponding to my stimulus and response patterns, then it seems that what the argument proves is that I am the only person in the world that has any mental states at all. Thus, for example, if I ask everybody in the room to put their thumbs on a desk and I go around pounding each thumb with a hammer to see which ones, if any, hurt; it turns out that as far as I can observe there is only one thumb that hurts: this one, the one I call mine. But when I hit the other thumbs, there is no feeling at all.
The view that I am the only person who has mental states is called “solipsism.” Solipsism comes in at least three different grades. One, the most extreme form: I am the only person in the world who has mental states; and indeed in some forms, nothing exists in the world except my mental states. Two, epistemic solipsism: maybe other people have mental states, but I can never know for sure. It is quite possible that they do but I have no way of finding out, because all I can observe is their external behavior. And three: Other people do have mental states, but I can never be sure that they are like mine. For all I know, what I call “seeing red,” if you could have that very experience you might call it “seeing green,” and if I could have your experience that you call “seeing red” I would call it “seeing green.” We both pass the same color blindness tests because we both make the same discriminations in our behavior. If asked to pick out the green pencil from a box of red pencils, we both pick the same pencil. But how do I know that the inner experiences you have that enable you to discriminate are similar to the ones I have that enable me to discriminate?
Solipsism is unusual in the history of philosophy in that there are no famous solipsists. Just about every conceivable crazy philosophical position has been held by some famous philosopher or other, but, as far as I know, no famous historical philosophers have ever been solipsists. Of course, if anyone were a solipsist it would hardly be worth his or her time to tell us that they were solipsists, because on their theory we don’t exist. *
Solipsism also involves a peculiar asymmetry in that your solipsism is no threat to me, and my solipsism, if I am tempted to solipsism, cannot be refuted by you. So, for example, if you come to me and say, “I am a solipsist. You don’t exist.” I do not feel the temptation to think, “Gosh, maybe he’s right, maybe I don’t exist.” But, correspondingly, if I am tempted to solipsism, it is no good my going to you and asking, “Do you exist? Do you really have mental states?” Because anything you say will still be consistent with the hypothesis of solipsism.
The skepticism about other minds that follows from Cartesian dualism is just a special case of a much more general kind of skepticism: skepticism about the existence of the external world. On Descartes’ view all I can have certain knowledge of are the contents of my own mind, my actual thoughts, feelings, perceptions, and so on. But what about the chairs and tables and mountains and rivers and forests and trees that I see around me? Do I have secure knowledge that they really exist and that I am perceiving them as they really are? It is important to understand that on Descartes’ view we do not directly perceive objects and states of affairs in the world. What we directly perceive, that is, perceive without any inferential processes, are the contents of our own minds. So if I hold up my hand in front of my face, what I directly perceive, what I strictly and literally perceive, according to Descartes, is a certain visual experience that I am having. Descartes calls these experiences “ideas.” I perceive not the hand in itself, but rather a certain visual representation of the hand, a kind of mental picture of the hand. But then the question arises, How do I know there really is a hand out there on the other side causing me to have this mental picture? Because I do not perceive the hand itself but only a mental representation of the hand, the question arises, How do I know that the representation really represents, or represents accurately? Descartes’ view was common in the seventeenth century. It is called the “representative theory of perception,” and I am going to tell you more about it later, but I want to point out at this stage that a problem for Descartes is, How can we really be sure? How can we have certain and secure knowledge that there is an object out there that is causing me to have this visual experience, and that the visual experience is in any respect an accurate representation of the real features of the object?
Descartes presents very little by way of an argument to show that we cannot directly perceive tables, chairs, mountains, etc. but can only perceive our ideas of these things. He makes the transition from perceiving real objects to perceiving only the contents of our own minds very casually. Though he was by no means the first philosopher to hold this view, the move from the view that we really perceive real objects to the view that we only perceive our ideas of objects is a move of decisive importance in the history of philosophy. Indeed, I would say it is the greatest single disaster in the history of philosophy over the past four centuries. In contemporary jargon, it is put by saying: we do not perceive material objects, we perceive only “sense data.” I will have much more to say about this issue in chapter 10.
There are really two closely related problems. The first is, How do we give an analysis of our perceptual interactions with the world? What exactly is the relationship between our inner perceptual experiences, on the one hand, and material objects and other features of the external world, on the other? The second is, How can we ever be sure that we have knowledge of the external world that is on the other side of our perceptual experiences? The two are closely related because we would like our analysis of perception of the external world to provide us with the tools for answering skepticism about the possibility of having knowledge of the external world.
I have experiences of making up my own mind, of deciding between genuine alternatives, and of doing one thing, when I could easily have done something else. These are manifestations of what I take to be my own freedom of the will. But the question naturally arises, Do I genuinely have free will, or is it only an illusion? The question comes in a very sharp form for Descartes, because if my free will is a feature of my mind, how can it have any effect on the physical world, if the physical world is entirely determined? This problem is an extension of, but not the same as, the mind-body problem. For even if we have a solution to the mind-body problem, even if we can show how my thoughts and feelings can move my body, there is still the question, How is this consistent with the conception of physics of Descartes’ time that the physical world is a completely causally closed, deterministic system? Every event that happens in the physical world is determined by preceding physical events. So even if we could prove somehow that we have mental free will, it wouldn’t make any difference to the behavior of my body, because the behavior of my body is caused by the preceding states of my body and the rest of the physical universe. The problem of free will seems difficult for anyone, but it raises exceptional problems for someone who accepts dualism.
This problem is still with us today in a form just as acute as that of Descartes’ time. Nowadays we think that quantum physics has shown an indeterminacy in the behavior of particles at the subatomic level. Not everything is determined in the way that classical physics supposed. But that seems to be no help with the free will problem, because the form of quantum indeterminacy is randomness, and randomness is not the same as freedom. The fact that particles at the microlevel are not completely determined, and therefore not completely predictable, but only statistically predictable, seems to give no support whatever to the idea that our apparently free actions are really free. Even if our decision making somehow inherited the indeterminacy of the quantum-level events in our brains, that would still not give us free will, but only an unpredictable random element in our decisions and behavior. I will say more about this in chapter 8.
There is another problem to which Descartes’ followers have thought his account provided a conclusive answer, even though Descartes himself did not address the problem directly: the problem of the existence of the self and its identity through time and change. To see what the problem is, consider this example: I am now working on a set of issues while looking out at a lake in Sweden. A month ago I was working on related problems while looking at the ocean off California. The experiences are quite different, but I think of them as both experiences of mine. Why? With what justification? There is really a whole set of questions here, a tangle of philosophy. What fact about these experiences makes them experiences of the same person and what fact about me makes me now the same person as the person who was in California? It is tempting to say that this person is the same as that person because they both have the same body. But is this body really essential to my identity? It seems at least possible to imagine that I might, like Gregor Samsa in the story by Kafka, wake up in a completely different body. But if the same body is not what makes me me, then what does make me me? What is the relation between my personal identity and my bodily identity? In addition to this or that particular experience, do I also have the experience of myself as a self?
The dualist’s answer to these questions is swift. My body has nothing whatsoever to do with my identity. My identity consists entirely in the continuation of the same mental substance, the same soul, or res cogitans. Material objects may come and go and experiences may come and go, but my identity is guaranteed by the sameness of my mental substance, for I am identical with that substance.
There are two other problems for Descartes that are more in the nature of puzzles that he has to resolve, but his solutions are quite interesting. These are the problem of nonhuman animals and the problem of sleep.
If every mind is a spiritual or mental substance, and if minds are indestructible, then it seems that if animals have minds, every animal has an immortal soul. But if it turns out that every dog, cat, mouse, flea, and grasshopper has an immortal soul, then, to put it mildly, heaven is going to be very much overpopulated. Descartes’ solution to the problem of animal minds was swift and brutal. He said that animals do not have minds. He was not at all dogmatic about that; he thought that perhaps they have minds, but it seemed to him scientifically unlikely that they had minds. He thought the crucial distinction between us and animals, that enables us to tell for sure that human beings have minds and animals do not, is that human beings have a language in which they express their thoughts and feelings, and animals have no language. Their lack of language he considered to be overwhelming evidence that they have no thoughts or feelings. Descartes agreed that this is a somewhat counterintuitive result. If we see a dog hit by a carriage and we hear the dog howling in apparent pain, it looks like we have to assume that the dog has feelings just as we do. But Descartes says all of that is an illusion. We should no more pity the dog than we pity the carriage when it is involved in a crash. The noise might make it look as if the carriage was suffering pain, but it is not; and likewise with dogs and all other animals. It sounds crazy to deny that dogs and other animals are conscious, but here is how I think Descartes thought of the matter. In the human case, the body is not conscious. It is only the immortal soul, which is attached to the body, that is conscious. But in the dog’s case, it seems very unlikely that there is an immortal soul; there is just a body, and bodies cannot be conscious. Therefore, the dog is not conscious. Ditto for all other animals.
The eighth problem for Descartes is the problem of sleep. If every mind is essentially conscious, if consciousness is the essence of mind such that you could not have a mind without being conscious, then it looks like unconsciousness would imply nonexistence. And indeed Descartes’ theory implies: if I cease to be conscious, then I cease to exist. But then how do we account for the fact that people, while still alive, nonetheless are often unconscious. They go to sleep, for example. Descartes’ answer to that would be that we are never totally 100 percent unconscious. There is always some minimal level of dreaming going on even in the soundest sleep. As long as we continue to exist we necessarily continue to be conscious.
There are four other problems arising out of the problems of fitting minds into the rest of the universe, which, however, were either not addressed by Descartes himself or have been transformed in the contemporary era in ways that are quite different from the forms in which Descartes and his immediate followers addressed them.
Intentionality is a problem that arises not only for dualism, but for the philosophy of mind in general. It was never explicitly faced by Descartes, but in subsequent philosophers it has come to the fore, and indeed in the past hundred years has become one of the central problems in the philosophy of mind.
“Intentionality” is a technical term used by philosophers to refer to that capacity of the mind by which mental states refer to, or are about, or are of objects and states of affairs in the world other than themselves. So, for example, if I have a belief, it must be a belief that something is the case. If I have a desire, it must be a desire to do something or that something should happen. If I have a perception, I must at least take myself to be perceiving some object or state of affairs in the world. All of these are said to be intentional, in the sense that in each case the state refers beyond itself. Intending, in the ordinary sense in which I intend to go to the movies tonight, is just one kind of intentionality among others along with belief, hope, fear, desire, and perception. (The English technical term comes not from the English “intention” but from the German Intentionalität and that in turn from Latin.) It is a special technical term, not to be confused with intending in the ordinary sense.
The special philosophical problem of intentionality is this: suppose that I now believe that George W. Bush is in Washington. The question arises, How can my thoughts, which are entirely inside my mind, reach out all the way to Washington, D.C.? If I think the sun is 93 million miles from the earth, how is it, again, that my thoughts can reach out and refer beyond themselves? The problem of how a mental state can refer to or be about something beyond itself is the problem of intentionality.
It is absolutely essential to be clear about the distinction between the intrinsic or original intentionality that I have in my head when I am thinking about something and the derivative intentionality that the marks on paper have when I write my thoughts down. The words on paper really do mean and refer, and thus have intentionality, but their intentionality is derived from mine when I intentionally wrote them down. Also we need to distinguish these two, the original and the derived, from metaphorical ascriptions, or as-if cases of intentionality. If I am now thirsty that is a case of intrinsic or original intentionality. If I write down the sentence, “I am thirsty” that sentence has derived intentionality. If I say, “My car is thirsty for gasoline” that sentence makes a metaphorical or “as-if” ascription of thirst to the car. But the car does not literally have any intentionality, either original or derived. I cannot tell you how much confusion has been generated by the failure to see these elementary distinctions.
In its modern form there are really two problems of intentionality. First there is the problem of how it is possible for events occurring in our brains to refer beyond themselves at all. How is aboutness or directedness possible at all? A second, related, problem is how is it that our brains or minds have the specific intentional contents that they do? So, for example, if I am now thinking about George W. Bush, what fact about me makes my belief have the content that it is about George W. Bush and not, for example, about his brother Jeb or his father George Bush or somebody else named George W. Bush or my dog Gilbert? The two problems are, How is intentionality possible at all? And given that it is possible, How is it that intentional states have the specific contents they do have? I devote chapter 6 to the problems of intentionality.
I said there were two parts to the mind-body problem, one going in and one going out. How do input stimuli cause mental phenomena, and how do mental phenomena cause output behavior? Each of these deserves separate discussion, so I am going to make the question of how mental states function causally into a separate topic.
Some philosophers who think that we could explain how consciousness is caused by brain processes cannot see how consciousness could have any causal powers of its own. Granted that somehow or other consciousness, and mental phenomena generally, are dependent on brain processes, it is hard to see how they could cause bodily movements or cause anything in the physical world. The view that mental states exist but are causally inert is called “epiphenomenalism.” On this view consciousness exists alright, but it is like the froth on the wave or the flash of sunlight reflected off the surface of the water. It is there but it does not really matter. It is an epiphenomenon. But this seems too counterintuitive. Every time I decide to raise my arm, it goes up. And it is not a random or statistical phenomenon. I do not say, “Well, that’s the thing about the old arm. Some days she goes up and some days she doesn’t.” The problem is to show how something not a part of the physical world could have such effects on the physical world. In the contemporary jargon this problem is posed as follows. It is often said, “The physical world is causally closed.” That means that nothing outside the physical world can enter into the physical world and act causally. How then could mental states, which are not physical and thus not part of the physical world, act causally on the physical world?
For Descartes, any mental activity is by definition conscious. The idea of an unconscious mental state is to him a contradiction in terms, an unconscious consciousness. But, in the past century or so, we have come to be quite comfortable with the idea that many of our mental states are unconscious. What can this mean? What is an unconscious mental state and how does it fit in with the rest of our mental life and with the world in general?
The problem of the unconscious is not one just for psychopathology. We do indeed say that people act from motives of which they are unconscious and the presence of which they would sincerely deny. We say that Sam was insulting to his brother Bob because he has an unconscious hostility to his brother. This is the sort of thing that Freudian psychology attempts to deal with. But there is another, more pervasive, use of the notion of the unconscious according to which we think of all sorts of mental processes as going on inside our brains but without any conscious manifestations. On standard theories of perception, we think that people perceive the shapes of objects by unconsciously inferring the real features of the object from the limited features of the physical stimulus with which they are presented. The problem for both of these notions of the unconscious is, what exactly is it supposed to mean in real terms? What facts about brain events could make them both mental and at the same time unconscious?
Explanations of human psychological and social phenomena seem to have a different logical structure from explanations in physics and chemistry. When we explain why we voted the way we did in the last election, or why the First World War broke out, we seem to be using a different sort of explanation from when we explain why plants grow. What are the appropriate forms of explanation for human psychological and social phenomena and what implications does this have for the prospects of the social sciences?
One of the most disappointing features of the intellectual history of the last hundred years was the failure of the social sciences to achieve the rich explanatory power characteristic of the physical and biological sciences. In sociology, or even economics, we do not have the kind of established knowledge structures that we have in physics and chemistry. Why not? Why have the methods of the natural sciences not had the kind of payoff in the study of human behavior and human social relations that they have had in the physical sciences?
A large part of this book will be concerned with the 12 problems that I have just outlined. If those problems look interesting to you, you are likely to find this book interesting. If you cannot for the life of you figure out why anybody would be interested in these problems, then this is probably the wrong book for you. The book is not a historical book, and I will not say a great deal about the development of these problems historically. However, since I introduced eight of them by way of Descartes as their origin, I want to tell you, however briefly, what his answers to these eight questions were. I think that, without exception, his answers were inadequate, and to his credit, he was often fully aware that they were inadequate. I think you will understand contemporary philosophy better if you see, at least briefly, how he dealt with these problems.
Descartes never got an answer to this question that he was satisfied with. He did recognize that the mind caused events in the body and that events in the body caused events in the mental realm. But how exactly was it supposed to work? He never felt he had resolved that. He studied anatomy and at least once observed the dissection of a cadaver to find out where the point of connection between the mind and the body might be. In the end he came up with the hypothesis that it must be in the pineal gland. This is a small pea-shaped gland at the base of the skull. Descartes thought that this must be where the mental forces and the physical forces come in contact with each other. This is not as crazy as it sounds; he gave a reasonable argument for thinking this. He noticed that everything in the brain has a twin on the opposite side of the brain. Because of the two hemispheres, the anatomy apparently occurs in duplicate. But since all of our mental events occur in a unitary form, there must be some unified point in the brain where the two streams are brought together. The only single unduplicated organ he could find within the brain was the pineal gland, so he assumed that the point of contact between the mental and the physical must be the pineal gland.
(The urge to find the point of contact between the soul and the body is still not dead. I once debated a Nobel Prizewinning neurobiologist, Sir John Eccles, on British television. He argued that the soul attaches to the brain in the supplementary motor area. Here is his argument: If you ask a subject to perform a simple motor task such as touching each of his right fingers with his right thumb, the motor cortex shows a high level of activity. If you now ask the subject to just think the task but not actually perform it, the motor cortex shuts down but the supplementary motor area remains active. The idea that Eccles had is that when the soul alone is active it is stimulating the supplementary motor area.)
In a famous passage Descartes said we should not think of the mind as lodged in the body like a pilot in a ship, but we should really think that it is somehow suffused throughout the body. If I bump into something I do not observe my body banging into another object in a way that the pilot of a ship might observe the ship banging into the wharf, but rather I feel a pain in the part of my body that comes in contact with the object. Descartes says we should think of our mind as if it were somehow suffused throughout the body, but on his own account, that cannot be a correct thing to say, because mental substance cannot be spatially extended. It cannot be spread throughout the body because it cannot be spread out at all.
Some version of the argument from analogy is often attributed to Descartes, but I have never been able to find it stated explicitly in his writing. According to the argument from analogy, I infer the existence of mental states in other people, by analogy with myself. Just as I observe a correlation of my own behavior with my mental states, so I can infer the presence of appropriate mental states in others when I observe their behavior. I have already pointed out the limitations of this form of argument. The problem is that in general with inferential knowledge there must be some independent check on the inference if the inference is to be valid. Thus for example, I might discover that a container is empty by banging on the container and inferring from the hollow sound that there is nothing in it, but this inferential form of knowledge only makes sense given the assumption that I could open up the container and look inside and thus noninferentially perceive that the container is empty. But in the case of knowledge of other minds there is no noninferential check on my inference from behavior to mental states, no way that I can look inside the container to see if there is something there.
Descartes has an elaborate argument that we can have certain knowledge about objects and states of affairs in the external world, even though all we directly perceive are the contents of our own minds. The first step in his argument requires that he prove the existence of God. And this is no mean feat in itself. But, assuming that God exists, he argues that God cannot be a deceiver. Because of God’s perfection, it would be inconsistent to suppose that he could be a deceiver, for deceit is an imperfection. But if God is not a deceiver, then there must exist an external world, and I must have some sort of correct knowledge when I make observations of the external world. Why? Because God gives me every reason to believe, for example, that there is a desk in front of me, and a chair on which I’m sitting, and no reason to suppose otherwise. Therefore, if I am mistaken, God would be deceiving me, and that is impossible.
This then raises a problem for Descartes: How is error is possible? And his answer is that error is possible because my will exceeds my understanding. My will is potentially infinite; my understanding is finite. And I often will to believe things that I do not clearly and distinctly perceive to be true, and consequently, I can be mistaken.
It is important to emphasize that Descartes did not think that our perceptions are in general accurate representations of the world. Objects do not really have colors, tastes, or smells, nor do they give off sounds, even though colors, tastes, smells, and sounds seem to us perceptually to be parts of the world. The point is that we can be certain that there is an external world causing our perceptions and we can get certain sorts of accurate information about it from our perception, even though much of our perceptual experience is illusory.
It seems to me that Descartes has no answer to this question beyond a mere assertion. He says I am free insofar as I feel myself to be free. But the problem, as we will see later, is that it is not at all clear that from the fact that I perceive myself to be free, I really am free.
Descartes never faced this question explicitly, but Cartesians have generally thought his dualism gives us an automatic solution to this problem. The self just is identical with a mental substance and the identity of the mental substance is simply guaranteed by the fact that it is the same mental substance. But it is hard to see how this is any kind of a solution other than a solution by fiat. How does the mental substance ever acquire all these mysterious powers and properties? And what reason have we to suppose that there is any such mental substance in addition to our physical bodies and our conscious experiences? As we will see, Hume made devastating criticisms of the Cartesian account of the self and personal identity. There is no experience of the self, according to Hume; and the identity that we ascribe to ourselves through the changes in our lives is an entirely fictitious identity. It is a kind of systematic illusion. Many other philosophers follow Hume in supposing that there is no such thing as a self in addition to the sequence of our particular experiences. Lichtenberg thought that the “I” in sentences such as “I think” gives us the illusion that there is an “I” that does the thinking; but he says we should say rather “It thinks,” where the “it” is like the “it” in “It’s raining.” It does not actually refer to an entity.
There is not just one problem of the self but several. I do not think Descartes' account of res cogitans is in any way a solution to these problems and I will address the whole bunch of them in chapter 11.
I have already criticized Descartes’ solutions to these problems so I will be very brief here: it seems to me simply preposterous to claim that animals do not have any conscious states. When I come home from work and my dog rushes out to greet me, wagging his tail and jumping up and down, why exactly is it that I am so confident that he is conscious and indeed that there is a specific content to his consciousness, he is happy to see me? The usual answer given to this question is that because his behavior is so much like that of a happy person I can infer that he is a happy dog. But that seems to me a mistaken argument. To begin with, happy people do not in general wag their tails and try to lick my hands. Furthermore, and more importantly, someone might easily build a robot dog that would wag its tail and jump up and down without having any inner feelings whatever. What is so special about the real dog? I think the answer is that the basis on which I am confident that my dog is conscious and has a specific content to his consciousness is not simply that his behavior is appropriate, but that I can see that the causal underpinnings of the behavior are relatively similar to mine. He has a brain, a perceptual apparatus, and a bodily structure that are relevantly similar to my own: these are his eyes, these are his ears, this is his skin, there is his mouth. It is not just on the basis of his behavior that I conclude that he is conscious, but rather on the basis of the causal structure that mediates the relation between the input stimulus and the output behavior. In the case of humans, the input stimulus causes experiences, which in turn cause output behavior. The underlying physical structure that enables the input stimulus to cause experiences is relevantly similar in humans and higher animals. For that reason we are completely confident that dogs and chimpanzees have conscious states, in many respects like our own. When it comes to snails and termites, we have to leave it up to the experts to tell us whether or not they have a rich enough neurobiological capacity to have conscious life.
Again, just as it seems preposterous to me to suppose that animals are not conscious, it also seems preposterous to me to suppose that we cease to exist if we become completely unconscious during sleep or under anesthesia. However, if Descartes is wrong to suppose that a continuation of consciousness is essential for a continuation of our very existence, then the question is raised, What exactly are the criteria for our continued existence? This is the famous problem of personal identity, which I will discuss further in chapter 11.
The 12 problems I have outlined form the framework for my discussions about the philosophy of mind. But I do not wish to give the impression that the subject is in this way limited. These problems open up into a variety of other problems that we will have to pursue. One thing we will discover is that often there are two sets of problems concerned with each of these issues. There is the overwhelming philosophical problem, the big-deal problem, as it were, then there is a detailed problem or set of problems about how the phenomenon works in real life. So, for example, with consciousness, there is the big-deal problem: How is such a thing possible at all? How could the brain cause consciousness? In current discussions this is often called the “hard problem” and the lack of an explanation of how the brain does it is called the “explanatory gap.” But there is also, I think, an equally interesting problem: How does consciousness function in actual organisms like ourselves? Similarly with intentionality. There is the huge problem: How is it possible that intentionality could exist at all? But, to me, at least, the more interesting question is: How does it work in detail?
What I have tried to do in this chapter is to present the framework for the discussions that will follow. The problems will not be treated as of equal weight. Not by any means. The next three chapters will be largely devoted to the mind-body problem. I have already said what I will have to say about animals and sleep. Several problems receive a chapter of their own: intentionality, mental causation, free will, the unconscious, perception, and the self. Some of the other problems, though they are of great importance, will receive only rather brief discussion in this book, because they go far beyond the philosophy of mind, especially skepticism and social science explanation. These are both large questions and I will discuss them only briefly in this book, because to give an adequate discussion would require a separate book.
* Bertrand Russell writes:
As against solipsism it is to be said, in the first place, that it is psychologically impossible to believe, and is rejected in fact even by those who mean to accept it. I once received a letter from an eminent logician, Mrs. Christine Ladd Franklin, saying that she was a solipsist, and was surprised that there were no others.
Human Knowledge: Its Scope and Limits (London: Allen and Unwin, 1948), 180.