Why I am neither a materialist nor a dualist: a dialogue

Dramatis Personæ:

Amber – a philosophy graduate student

Woody – a philosophy graduate student and a materialist

Madhva – a philosophy graduate student and a dualist

Part I

Amber: Hey, guys. Arguing again?

Madhva: Yep.

Amber: I don't really understand either of your positions.

Woody: Well, it's pretty simple, isn't it? I'm a materialist, and Madhva is a mind-body dualist.

Amber: What's materialism? Define it for me.

Woody: Well, I guess it's the belief that all substances are material.

Amber: That doesn't help me. I'm not sure what objects count as substances. Is a plastic chair a substance, or is it only an accidental modification of plastic? Is plastic a substance, or is it only an accidental modification of carbon?

Woody: Let's just define a substance as anything that isn't a property of something else. So both a plastic chair and its plastic would be substances.

Amber: In that case, aren't there some immaterial substances? Light isn't a property of anything else, so it's a substance, but it's a different kind of thing than matter.

Woody: You're wrong. Haven't you heard of E = mc²? Energy, such as light, has mass. So it's really a form of matter.

Amber: Well, okay. But that's a relatively recent discovery. Suppose that E = mc² weren't true. Suppose that light didn't have mass and weren't a form of matter. Even if that were true, you wouldn't feel forced to renounce your materialism, would you?

Woody: No, I guess not.

Amber: So, by "materialism", you can't really mean the belief that all substances are material.

Woody: Okay, let's define materialism this way: the belief that all substances are physical.

Amber: What does "physical" mean?

Woody: I guess it means "located in space". Matter and light are both physical, because they're both located in space. God and Cartesian minds, if they existed, would not be physical, because they would not be located in space.

Amber: So materialism is the belief that all substances are located in space?

Woody: Yes.

Amber: But that kind of materialism doesn't rule out property dualism. That kind of materialism just talks about substances; it doesn't even address properties. I thought that materialists wanted to rule out property dualism, not just substance dualism.

Woody: Okay, let's try again. In the context of philosophy of mind, materialism is the belief that every mental property is identical with some physical property (or set of properties).

Amber: There's that word "physical" again! Can you define materialism without using it?

Woody: I'll try. Materialism is the belief that every mental property is identical with some property (or set of properties) that can be identified without using mental terms like "subjective", "experience", "mind", etc. For example, pain is identical with, say, C-fiber stimulation, something that can be identified without using mental terminology. Or perhaps any internal state counts as pain as long as it performs the right functional role in an organism—again, something that can be identified without using mental terminology.

Amber: Can't even a substance dualist say that mental properties can be identified without using mental terminology? I mean, even if substance dualism is true, can't we identify happiness by saying, "Happiness is the property that causes people to smile"?

Woody: Well, we can say that in our world, because in our world happiness causes smiling. But if substance dualism is true, then happiness is a property of immaterial minds. If those immaterial minds exist, then there are possible worlds in which bodies don't smile when their immaterial minds feel happiness. So if substance dualism is true, then we can't identify happiness across all possible worlds by saying, "Happiness is the property that causes people to smile". So let's define materialism like this: materialism is the belief that every mental property is identical with some property (or set of properties) that can be identified across all possible worlds without using mental terminology. So a materialist would say that pain is identical across with C-fiber stimulation or with a certain functional state—properties that can be identified across all possible worlds without using mental terminology. Although it isn't immediately obvious, pain and C-fiber stimulation (or pain and the filling of a certain functional role) are really the same property.

Amber: If that's what materialism is, then I reject materialism. I just don't understand how pain and C-fiber stimulation could "really" be the same property. In fact, I don't understand how any two properties could "really" be the same property. For example, consider roundness and the ability to roll. These two properties may always occur together: it may be the case that every round object has the ability to roll and everything that can roll is round. But I don't even understand what it would mean to say that roundness and the ability to roll are "really" the same property. Roundness is roundness, and the ability to roll is the ability to roll.

Woody: Aren't there some cases where two properties are really the same property? What about the property of fatherhood and the property of being a male parent? Aren't they really the same property?

Amber: Okay, you're right. "Father" and "male parent" mean the same thing by definition. So of course the property of fatherhood and the property of being a male parent are the same property. I spoke too quickly. What I should have said is this: if property F and property G are not identical by definition, then I don't understand how F and G could be the same property.

Woody: Aren't you giving properties special treatment? After all, you wouldn't say the same thing about, say, the morning star and the evening star. The morning star and the evening star aren't identical by definition, but they are in fact the same object—namely, the planet Venus. Why is it different with properties?

Amber: The morning star and the evening star are identified by means of different sets of properties. In particular, the morning star is identified by its property of appearing in the morning, whereas the evening star is identified by its property of appearing in the evening. Now, it happens that these two sets of properties belong to the same object. So we can say that the morning star and the evening star are the same object. Since I'm not a substance dualist, I'd say something similar about the mind and the brain. They are identified by means of different sets of properties: the brain is identified by means of properties like its location in the skull; the mind is identified by means of its properties of consciousness, intelligence, etc. It happens that these two sets of properties belong to the same object. So we can say that the mind and the brain are the same object. But you thoroughgoing materialists want to go farther. You want to say the same thing about the properties themselves. I just don't see how that's supposed to work.

Woody: Really? Aren't there a lot of cases where we discover that two properties are really the same property, even if they aren't identical by definition? For example, we discovered that temperature is really average molecular motion.

Amber: Wouldn't it be more accurate to say that we redefined temperature as average molecular motion? "Temperature" used to mean the power to produce sensations of heat and cold in us. That power is not itself identical with molecular motion. But once we discovered that the power to produce sensations of heat and cold is correlated with average molecular motion, we redefined "temperature", at least for scientific purposes, as average molecular motion. If that's correct, then your temperature example isn't an example of discovering that two properties are really the same property.

Woody: I don't think that "temperature" originally meant the power to produce sensations of heat and cold in us. I think that "temperature" has always meant something like "the property (whatever it is) that causes sensations of heat and cold in us". We've discovered that sensations of heat and cold are caused by average molecular motion. Thus, we've discovered that temperature is identical with average molecular motion.

Amber: Let's assume that you're right about the meaning of the word "temperature". In that case, the temperature example isn't analogous to the pain example. Temperature is defined as a property that causes certain sensations. Thus, whatever property turns out to cause those sensations will turn out to be identical with temperature. But pain isn't defined as a property that causes certain sensations. By "pain", we do not mean "the property that causes painful sensations in us". Pain doesn't cause our painful sensations; it just is those sensations.

Part II

Madhva: Given what you've said so far, Amber, shouldn't you call yourself a property dualist? You think that mental properties aren't identical with physical properties. That's property dualism.

Amber: No, I said that mental properties aren't identical with properties that can be identified across all possible worlds without using mental terminology. I didn't say that mental properties aren't identical with "physical" properties. I don't understand the distinction that property dualists draw between the "physical" and the "non-physical".

Madhva: Surely you have a concept of physical and non-physical substances?

Amber: I guess so. If I have a concept of physical and non-physical substances, then it's just the concept that we mentioned earlier: physical substances are located in space; non-physical substances, if they exist, aren't located in space. In that case, "non-physical" means "not located in space". If "non-physical" means "not located in space", then aren't all properties non-physical? My red shirt is located in space, but it's a category mistake to say that the shirt's redness is located in space. Therefore, the redness is just as non-physical as my mental properties.

Madhva: Can't we say that your shirt's redness is located in space, since it belongs to your spatially-located shirt?

Amber: In that case, my mental properties are also located in space, since they belong to my spatially-located brain. Either way, my mental properties are no more or less "physical" than any other properties that I have.