Presentation

Chapter 19 Dualism and the Mind/Body Problem

Chapter Outline 1. What Is the Mind/Body Problem? 2. Descartes’ Dualism 3. The Mind/Brain Identity Theory 4. Immortality of the Soul 5. Leibniz’s Law 6. Descartes’ First Argument for Dualism—The Indubitable Existence Argument 7. An Analogy 8. Propositional Attitudes and Aboutness 9. Descartes’ Second Argument for Dualism—The Divisibility Argument 10. Causality between the Physical and the Nonphysical

In this fourth part of the book, on philosophy of mind, I’ll discuss three problems—the mind/body problem (Chapters 19– 23), the problem of free will (Chapters 24– 26), and the problem of psychological egoism (Chapter 27). The mind/body problem and the problem of free will both address the broad issue of how the mind is related to the physical world of cause and effect. Are minds physical things (for example, are they identical with brains?), or are they nonmaterial? If your beliefs and desires are caused by physical events outside of yourself, how can it be true that you act the way you do of your own free will? The last problem—the problem of psychological egoism—concerns the motives that drive us to act. Are people genuinely moved by the welfare of others, or is all behavior, in reality, selfish? These three problems concern different stages in the causal chain that leads from genes and environment, to the mind, and then to action:

The mind/body problem concerns the nature of the objects and events that exist at stage 2 in this diagram. What is a mind? What are beliefs and desires? The problem of free will concerns the relation of stage 1 and stage 2. If our beliefs and desires are caused by the genes we possess and the environments we have inhabited, how can we possess free will? The problem of psychological egoism concerns the relationship of stages 2 and 3. If the actions we perform are caused by the desires we have, won’t it be true that all action is fundamentally selfish—aimed at satisfying the actor’s own desires, not at satisfying the needs of others? These are preliminary statements of the three philosophical problems. Each needs to be refined.

What Is the Mind/Body Problem? The question posed by the mind/body problem is simple: What is the relationship between the mental and the physical? You have a mind, which contains various beliefs, desires, sensations, and emotions. You also have a brain; this physical thing is a structured piece of tissue containing an intricate web of neurons. Are your mind and your brain one and the same thing? Are your beliefs, desires, emotions, and sensations identical with physical things found in your brain? Or are your mind and your brain different objects? Perhaps the mind isn’t a physical thing at all.

Descartes’ Dualism In the previous section, the discussion of Descartes focused on his epistemology. Descartes also advanced a solution to the mind/body problem. It is this view, now called Cartesian Dualism, that I’ll now discuss. Dualism is the idea that there are two kinds of things in the world. There are physical objects on the one hand, and, on the other, there are mental objects (like minds, pains, and beliefs). According to dualism, brains and the bodies in which they are found are physical things; the mind, which is a nonphysical object, is distinct from both the whole body and is also distinct from all of the body’s physical parts. Descartes didn’t deny that there are causal interactions between the mental and the physical; taking aspirin can cure headaches, and the sound of trumpets can lift your spirits. In the other direction, it seems undeniable that beliefs and desires can cause the parts of your body to move in various ways (speaking, walking, etc.). But granting this two-way interaction did not lead Descartes to abandon dualism.

Read Meditation VI from Meditations on First Philosophy on www.mysearchlab.com

The Mind/Brain Identity Theory One alternative to dualism is provided by the Mind/Brain Identity Theory. This theory makes a claim about objects and also about the properties those objects possess. First, it says that your mind and your brain are one and the same object. Second, it claims that the mental properties you have (for example, believing that fire is hot, or wanting some ice cream, or being in pain) are physical properties; to be in pain is to have a certain type of physical event occur in your central nervous system.

The identity theory asserts that mental terminology and physical terminology describe the same items in the world. The following analogy may be instructive. For a long time, people used the term “water” to denote various items in the world. This term was used in

everyday life. At a certain point in the history of science, it was discovered that water is made of H2O molecules. The discovery was that water and H2O are one and the same thing. There certainly is a difference between the two pieces of terminology “water” and “H2O.” The first word has been used by ordinary people for a very long time. The second term was introduced much more recently, as part of a scientific theory. Yet it does not follow from these facts about the two terms that the terms denote different things. Water is identical with H2O, as chemists have discovered. Philosophers who defend the Mind/Brain Identity Theory say that the same point applies to the relationship of mental terms and neurophysiological terms. Common sense has for a very long time deployed such terms as “belief,” “desire,” “pain,” and “mind.” The identity theory suggests that what happened to water will happen to the mind. Eventually neurophysiology will discover the nature of the mind, just as chemistry discovered the nature of water. Once various scientific theories have been developed, we will understand what it is to believe that snow is white, what it is to want some coffee, what it is to feel pain, what it is to have a mind. In each case, the answer will be given in the vocabulary provided by brain science. We now have only a very partial picture of what these neurophysiological theories will be like. However, the identity theory predicts that science is headed in the direction of a purely materialistic account of the mind. The mind is a physical thing, even though we now have only an incomplete picture of what its physical nature is.

In addition to dualism and the Mind/Brain Identity Theory, there are other solutions to the mind/body problem that I’ll discuss. These are logical behaviorism (Chapter 20) and functionalism (Chapter 23). Rather than describing them right now, I’ll turn to the task of analyzing Cartesian Dualism.

Immortality of the Soul Before I present Descartes’ arguments for dualism, I should note a connection between the mind/body problem and an issue in the philosophy of religion. If you believe the doctrine of the immortality of the soul but also hold that the body disintegrates at death, you may be attracted by dualism. The issue of whether the soul is immortal, of course, isn’t the same as the question of whether there is a God. After all, there are many religions that deny the immortality of the soul. Conversely, someone might hold that the soul survives the death of the body and yet deny that there is a God. But historically it is worth remembering that what we might call “traditional” Christianity (this includes the Christianity of Descartes’ time) espouses the doctrine of immortality. Dualism makes room for this possibility.

If the soul is part of the mind (even if it isn’t the entirety of the mind) and if the soul lives forever and the body does not, we have an argument for dualism. However, this isn’t Descartes’ argument for dualism. Why not? Perhaps the reason is that anyone who doubts dualism will also probably doubt that any part of the mind survives the death of the body. So you aren’t going to convince anyone that dualism is true by beginning with the premise that the soul is immortal.

Leibniz’s Law Note a structural feature of the argument for dualism that I just described. The argument defends dualism by trying to find a property that the mind has but the brain lacks; the property in question is immortality. Quite apart from whether this argument is successful, we should note a perfectly sensible principle that it uses. The idea is that if m and b are identical, then they must have all the same properties. This principle is called Leibniz’s Law, after the seventeenth-century philosopher/mathematician (who, incidentally, co-invented the calculus with Newton. In Chapter 7, I briefly discussed Leibniz’s belief that we live in the best of all possible worlds). Leibniz’s Law is sometimes called the principle of the indiscernibility of identicals. It states that if you can find even one property that m has and b lacks, then you will have shown that m and b are distinct entities. You’ll see this principle at work in both of the arguments that Descartes presents for dualism. The following form of argument is deductively valid: • m has property P.

• b does not have property P.

• If m has a property that b lacks, then m ≠ b.

•

• m ≠ b.

Be sure you see how the argument concerning immortality has this logical form. The argument is valid. This means that if you reject the conclusion, you must reject at least one of the premises. I suggest that the third premise (Leibniz’s Law) is true. Therefore, if you reject the conclusion, you must reject one of the first two premises.

Descartes’ First Argument for Dualism—The Indubitable Existence Argument Now let’s look at Descartes’ first argument for dualism. In Chapter 13, I discussed how Descartes uses the method of doubt in his epistemology. He also uses the idea of doubt in his discussion of the mind/body problem.

Read Meditation VI from Meditations on First Philosophy on www.mysearchlab.com In the Second Meditation, Descartes claims you can’t doubt that you have a mind. If you try to doubt that you have a mind, you will find yourself entertaining a thought, and so you

must grant that you have a mind after all. Descartes thought that the existence of the body has a quite different status. He thought that it ispossible for you to doubt that you have a body. After all, you can entertain the thought that you are a disembodied spirit. Descartes concludes that your mind has a property that your body lacks. You can doubt the existence of the one, but not the existence of the other. Dualism follows, by Leibniz’s Law.

Perhaps you are suspicious of what Descartes says about your body. Is it really possible for you to doubt that you have a body? Can you conceive of yourself being a disembodied spirit? You should also consider Descartes’ other premise. Is Descartes right that you can’t doubt that you have a mind?

I’m not going to pursue these questions here. I’ll grant Descartes that he can’t doubt that he has a mind and that he can doubt that he has a body. I want to consider whether dualism validly follows from these premises. To see whether this follows, we must be very explicit about what the property is that the mind is said to have and the body is said to lack. Descartes claims that his mind has the property of indubitable existence, and that his body lacks that property. Let’s look more closely at this property. For an object X to have this property means that the “owner” of X can’t doubt that X exists. I say “owner” since my mind does not have indubitable existence for you. I take it that you have no trouble entertaining the thought that I don’t have a mind. It is the first-person case that matters here—a person can’t doubt the existence of his or her own mind.

An Analogy There is a subtle mistake in Descartes’ argument. I’m going to argue that indubitable existence is not a genuine property at all.

I’ll illustrate this idea by an example. Lois Lane wants to marry Superman. She doesn’t realize that Superman and Clark Kent are one and the same person. Clark Kent, you’ll recall, is the most incompetent reporter at the Daily Planet. If you ask Lois whether she wants to marry Clark Kent, she will say “No!” Does it follow from this (via Leibniz’s Law) that Superman and Clark Kent are two different people? Of course not. The following argument is not valid:

• Lois Lane wants to marry Superman.

• Lois Lane does not want to marry Clark Kent.

•

• Superman is not identical with Clark Kent.

On the surface, it looks as if this argument is valid, given Leibniz’s Law. It describes a property that Superman has and Clark Kent lacks and concludes that they are nonidentical. What you must see is that the argument does not describe any such property. Leibniz’s

Law, properly understood, does not license the conclusion of nonidentity. The two premises are true, but the conclusion does not follow from them; it is false.

Superman and Clark Kent have exactly the same properties. This isn’t contradicted by the fact that Lois Lane wants one of the following propositions to be true and the other to be false:

• Lois Lane marries Superman.

• Lois Lane marries Clark Kent.

The fact that Lois desires one of these propositions to be true and the other to be false does not show that Superman and Clark Kent have different properties. The propositions are different; the people are identical.

Likewise, Descartes says that I am able to doubt one, but not the other, of the following two propositions:

• I have a brain.

• I have a mind.

But from this, it does not follow that my brain has a different property from my mind. The propositions are different, but that doesn’t show that your brain and your mind are different objects.

Propositional Attitudes and Aboutness The crucial distinction we have to note here is this: doubting and desiring are attitudes we have towards propositions; doubting, desiring, and believing are examples of propositional attitudes. Perhaps there are some propositions whose truth cannot be doubted, whereas there are other propositions that we are able to doubt. Surely we desire that some propositions, but not others, should be true. But separate from this issue concerning propositions is the issue of what objectsthose propositions are about. Here is the lesson I draw from the example about Lois Lane: Even if one proposition is desired whereas another is not, it does not follow that what the first proposition is about differs from what the second proposition is about. The same point holds when we consider other propositional attitudes, like doubting. What follows from these two statements?

• Lois Lane wants it to be true that Lois Lane marries Superman.

• Lois Lane does not want it to be true that Lois Lane marries Clark Kent.

What follows is that the proposition Lois Lane marries Superman is a different proposition from the proposition Lois Lane marries Clark Kent. What does notfollow is that the person the first proposition is about (Superman) differs from the person the second proposition is about (Clark Kent). (Note to the reader: if you think that Superman and Clark Kent are different individuals, please invent an example in which a single person has two names and show how this example illustrates the relevant point about propositional attitudes and aboutness.)

What follows from these two statements?

• I can’t doubt that I have a mind.

• I can doubt that I have a body.

What follows is that the proposition I have a mind is a different proposition from the proposition I have a body. What does not follow is that the object the first proposition is about (my mind) differs from the object the second proposition is about (my body).

With this diagnosis in hand, let’s go back to Descartes’ argument for dualism. He says that his mind has the property of indubitable existence, whereas his body does not have that property. It sounds as if Descartes is describing a property that the one thing has but the other thing lacks. But this, I claim, is deceptive. Indubitable existence is not a property of an object; rather, doubting is something we do or fail to do to propositions. To say that my mind indubitably exists is just to say that I cannot doubt a particular proposition. To say that my body does not indubitably exist is just to say that I can doubt a particular proposition. From this difference between propositions, however, nothing follows concerning whether those propositions are about the same or different things. Descartes’ first argument for dualism is invalid.

Sense and Reference The philosopher/logician Gottlob Frege (1848–1925) wanted to explain a difference that separates the following two statements:

• The Evening Star is the Evening Star. • The Evening Star is the Morning Star. The first of these is obviously true; it is a logical truth of the form “a = a.” It is a priori; anyone who understands the meanings of the terms in this sentence will be able to see that it is true, there being no need for astronomical observation. The second statement is different. It describes a discovery that astronomers made; it is a posteriori. The phrase “the Evening Star” is used to refer to the first star to appear in the evening. “The Morning Star” is an expression that is used to refer to the last star to disappear in the morning. It was discovered that these are one and the same object—namely, the planet Venus. Notice that the terms occurring in the two statements refer to exactly the same thing. How, then, can the statements express different thoughts? Frege said that the explanation of this

fact is that terms have sense (meaning) as well as reference. Although “the Morning Star” and “the Evening Star” are terms that refer to the same thing (the planet Venus), the two expressions aren’t synonymous; they have different meanings. Frege thought that synonymous terms must refer to the same thing, but that terms that refer to the same thing need not be synonymous. The meaning of a term determines its reference, but not conversely. He also believed that the “truth value” of a statement (that is, whether the statement is true or false) is settled just by the reference of the terms it contains. Consider the statement “The inventor of bifocals is dead.” This statement is true. If Frege were right to say that the truth value of a statement is determined by the reference of the terms it contains, then we should be able to remove a term from this statement, replace it with a coreferring term, and have the resulting statement still be true. We can do this: “the inventor of bifocals” and “the first U.S. ambassador to France” are coreferential. Substituting one for the other, we obtain the following sentence: “The first U.S. ambassador to France is dead.” This statement is true. In this case, a true statement remains true if one of its terms is replaced by another that is coreferring.

Statements describing propositional attitudes posed a problem for Frege. Even though “Superman” and “Clark Kent” refer to the same person, the first, but not the second, of the following statements is true: • Lois Lane wanted to marry Superman. • Lois Lane wanted to marry Clark Kent. To account for this fact, Frege suggested that terms in such sentences don’t refer to the objects that they normally refer to. Normally, “Superman” and “Clark Kent” refer to a person. But in the above pair of sentences, Frege claimed that a shift occurs; the first refers to the meaning of the term “Superman,” whereas the second refers to the meaning of the term “Clark Kent.” Since these terms have different meanings, it won’t be true that the terms in the first sentence refer to precisely the same things that the terms in the second sentence refer to. This makes it possible for the first sentence to be true and the second false. In this way, Frege was able to retain his principle that the truth value of a sentence is determined by the reference of its constituent terms.

When you say, “Lois Lane shook hands with Superman,” you are referring to Superman. When you say “Lois Lane wanted to marry Superman,” you aren’t referring to Superman, according to this proposal of Frege’s. If you believe that you are referring to Superman in both statements, then you will reject Frege’s account of how statements about propositional attitudes should be understood.

Descartes’ Second Argument for Dualism—The Divisibility Argument I now turn to Descartes’ second argument for dualism. It is far simpler than the one just analyzed. In the Sixth Meditation, Descartes claims that physical things have spatial parts. For example, a surgeon could divide my brain into pieces. My mind, however, does not have spatial parts. If so, dualism follows, by Leibniz’s Law. Descartes also says that the body, but not the mind, has extension. By this he means that the body, but not the mind, takes up physical space; it has spatial location. This also leads to dualism, by Leibniz’s Law.

I’ll treat these two arguments together: if the body has the properties of divisibility and extension, but the mind does not, dualism follows. I think that Descartes’ argument here is valid. The question is whether his premises are true. I’ll grant Descartes that it sounds odd to say that my mind has spatial parts and that it is located between my ears. It also sounds strange to say that my mind weighs about five pounds and has blood vessels running through it. How are we to explain the fact that such claims sound funny to us? One explanation is that they can’t be true. If this were right, dualism would follow, since we then would have cited properties that my brain has but my mind does not. However, there is another possible explanation for why it sounds odd to say that my mind has spatial parts, or weighs five pounds, or has blood vessels running through it. The explanation is that these ideas are unfamiliar. The assertions sound jarring because they radically depart from what we happen to believe.

Consider the claim that water is H2O. Before the advent of the atomic theory, the claim that a liquid is made of numerous tiny particles that are too small to see may have sounded pretty strange to some people. But this, of course, does not mean that water could not be made of molecules of H2O. For this reason, I claim that Descartes’ second argument for dualism is inconclusive. If the mind and the brain are really identical, then many surprising facts may follow. I conclude that Descartes’ arguments for dualism do not work. The first argument (involving the idea of indubitable existence) is invalid. The second argument (involving the ideas of divisibility and extension) is valid, but it begs the question. There seems to be no reason to accept the premises (that the mind is indivisible and lacks extension) unless you already believe that the conclusion (dualism) is true. These negative verdicts don’t show that dualism is false. All I’ve claimed so far is that these two arguments for dualism are unsuccessful. I now turn to a criticism that has been made of dualism.

Causality between the Physical and the Nonphysical One of the main stumbling blocks for dualism has been the idea, endorsed by Cartesian Dualism, that there can be causal interactions between physical and nonphysical things. Descartes thought that physical events in your body can cause sensations in your mind. These sensations, like all mental events, allegedly lack spatial location. But how can events that are located in space bring about events that lack spatial location? And how are causal relations in the opposite direction possible? In The Passions of the Soul, Descartes claimed that the pineal gland in the brain is the jumping-off point for this interaction. Nerve impulses reach the pineal gland and then manage to affect the mind, even though the mind is not located anywhere at all. Conversely, your mind (which is no place at all) influences your body by making an impact on the pineal gland. This is pretty mysterious, and dualists since Descartes have not managed to make this process any more comprehensible.

Causality is something we understand best when we consider two physical events that are linked by a physical signal. When we say that throwing the switch on the wall caused the ceiling light to go on, we are talking about two physical events that occur at different times and at different places. These two events are connected by the flow of electricity. We not only know that throwing the switch caused the light to go on; we also know how throwing the switch managed to bring this about. If we were unable to detect a physical signal passing from the switch to the light, we would be puzzled about how the first event was able to cause the second. Similarly, if I said that throwing the switch caused an event that isn’t located anywhere at all, you would be puzzled how electricity or any other physical signal could reach an event that has no spatial location.

In light of the difficulty of understanding how causality can “cross over” from the mental to the physical and back again, wouldn’t it be simpler to account for the causal interaction of the mind and the body by adopting the identity theory? If the mind and the brain are identical, it isn’t terribly puzzling how your beliefs and desires can cause you to behave in various ways. This doesn’t prove that the Mind/Brain Identity Theory is correct; the point is just that what is a hard question for dualism to answer isn’t especially hard for the identity theory.

Review Questions 1. What does dualism assert? What is the Mind/Brain Identity Theory? 2. What is Leibniz’s Law? How is it used in arguments supporting dualism? 3. “I can’t doubt that I have a mind, but I can doubt that I have a body. Hence, my mind

isn’t identical with my body.” Is this argument valid?

4. “My brain is divisible into spatial parts, is located between my ears, weighs about five pounds, and has blood vessels running through it. My mind has none of these properties. Hence, my brain and my mind are nonidentical.” Is this argument valid? If it is valid, must dualism be true?

5. Dualism has been thought to make mysterious how the mind and the body can causally interact. What problem is involved here?

Problems for Further Thought 1. Descartes says that he can conceive of himself being a disembodied spirit (that is,

having a mind but not a body). What does conceiving of something mean? Does Descartes’ claim entail that it is possible for him to be a disembodied spirit? (See discussion of conceivability and possibility in Chapter 8.)

2. Is a statue identical with the stone it is made of? Is an organism identical with the collection of cells in its body? Can Leibniz’s Law be used to show that either of these claims of identity is false?

3. In the Sixth Meditation, Descartes argues that he is essentially a thinking thing. An essential property of a thing is a property that the thing must have if it is to exist. Could Descartes be deprived of thought and still be Descartes? Could Descartes have been born without the capacity of thought and still be Descartes? If Descartes can’t doubt that he thinks, is that enough to show that Descartes is essentially a thinking thing?

4. It was suggested in this chapter that we understand causality best when there is a physical signal that passes from cause to effect (the electricity example). However, the fact that “absences” are sometimes causes suggests that causality need not involve a physical signal. For example, suppose a patient dies because his doctor fails to give him medicine. There is no “physical signal” between doctor and patient in this case, but there is causation. Does this point solve the objection to dualism that concerns the nature of causality?

5. Frank Jackson (in “What Mary Didn’t Know,” Journal of Philosophy 83 [1986]: 291– 95) gives the following argument against physicalism (which he takes to be the claim that all facts are physical facts):

Mary is confined to a black-and-white room, is educated through black-and-white books and

through lectures relayed on black-and-white television. In this way she learns everything there

is to know about the physical nature of the world. She knows all the physical facts about us and

our environment, in a wide sense of “physical” which includes everything in completed physics,

chemistry, and neurophysiology, and all there is to know about the causal and relational facts

consequent upon all this, including of course functional roles. If physicalism is true, she knows

all there is to know. For to suppose otherwise is to suppose that there is more to know than

every physical fact, and that is what physicalism denies.

Physicalism is not the noncontroversial thesis that the actual world is largely physical, but the

challenging thesis that it is entirely physical. This is why physicalists must hold that complete

physical knowledge is complete knowledge simpliciter. . . . The claim here is not that, if

physicalism is true, only what is expressed in explicitly physical language is an item of

knowledge. It is that, if physicalism is true, then if you know everything expressed or expressible

in explicitly physical language, you know everything.

It seems, however, that Mary does not know all there is to know. For when she is let out of the

black-and-white room or given a color television, she will learn what it is like to see something

red, say. This is rightly described as learning—she will not say “ho, hum.” Hence, physicalism is

false.

Assess Jackson’s argument using the ideas concerning aboutness and propositional attitudes presented in this chapter.

Supplementary Reading RENÉ DESCARTES

Correspondence with Princess Elizabeth One of the primary challenges to any dualist theory is accounting for the interaction between material bodies and immaterial souls. For example, how can the decision to pick up a pencil cause your arm to move? In her correspondence with Descartes, Princess Elizabeth of Bohemia raises this worry as an objection to Descartes’s dualism.