One view of the mind says that connected to every body that has a mental life--every body that thinks, has experiences, is conscious of itself, and so on--is a separate, non-physical thing we can call a soul. The body is one thing, a physical thing; and the soul is another, independent and non-physical thing. While the body is alive, the soul is connected to it, but it's possible for the soul to go on existing even after the body is destroyed.

The view of the mind is called dualism, because its proponents think that there are two kinds of things in the world: physical things, like rocks and trees and human bodies, and these non-physical "souls." The souls aren't made up of physical parts. In principle, they can exist independently of any bodies or other physical things. The dualist says that in order to have a mental life--in order to think, have feelings, and so on--you need to have one of these "souls" connected to your body.

Comment: Many dualists would say that you just are your soul. But we won't try to settle that question in this class. We'll just worry about whether there needs to be a soul, in order for any thinking to be going on.

Some dualists have more complicated views, where souls are required for some kinds of mental processes (e.g. reflective thought) but not for others (e.g. on some views, animals can have pains and other bodily sensations without having souls). We'll stick with the simpler forms of dualism for now.

The dualist says there are two kinds of things in the world. Other theorists say there is only one kind of thing.

  • The materialist doesn't believe in any non-physical souls. He thinks everything in the world is really physical. Some of these physical things (like rocks and trees) are unable to think or have experiences, but the materialist thinks that other physical things (human bodies) are able to think and have experiences. They have mental lives, without having any non-physical souls.

    Materialism was originally the view that everything is made of matter. (That's why it's called "materialism.") Nowadays, though, philosophers have broadened the meaning of this term, so that you can still be a materialist even if you believe in gravitational fields, curves in space-time, and other things which are clearly not matter. Basically, the materialist believes in whatever our best physics tells us about.

  • The idealist says that there are no material things, there are only minds and thoughts and experiences. There is no mind-independent, physical table here; there are only certain experiences I have as if there's a table.

    You've probably all heard the following philosophical problem: Suppose a tree falls in the forest but there's no one there to hear it. Does it make a sound?

    One answer says:

    Yes, it does make a sound: because a sound is a physical phenomena, perhaps some wave patterns in the air. Those wave patterns can exist even if no one's there to hear them.

    The other answer says:

    No, a sound is essentially something that has to be experienced. If no one hears it, then it can't be a sound.
    Some want to say the same thing about colors: if no one sees them, then they can't really exist.

    The idealist is someone who holds that kind of view not just about sounds and colors, but about everything: about rocks and trees and even their own bodies. If they're not experienced then they don't really exist. Really nothing can exist except for minds and the thoughts and experiences that those minds have.

In this class we won't be talking very much about idealists. We'll be concentrating on the debate between dualists and materialists. So we'll take it for granted that things like tables are real, mind-independent things made up of matter. The question we're interested in is whether, in addition to material things like rocks and trees, there are also these non-physical souls.

Before we consider arguments for or against dualism, we first need to understand better what it is the dualist believes.

What does she mean when she says "There are two kinds of things in the world?"


A substance is:

  • an individual thing, not a property or event. It's the sort of this which has properties, and which might change its properties over time

  • a concrete thing, not something abstract like a number or a set

    Comment: It's a hard and controversial question how to explain this contrast between concrete and abstract. At a first approximation, abstract things are things that exist outside space and time and are causally inert. Numbers and sets are paradigm examples. Concrete things are the things that aren't abstract. Note that "concrete" doesn't just mean "physical." It might be true that every concrete thing is a physical thing, but if so, that's supposed to be a substantive philosophical thesis, and not just part of the definition of "concrete."

    If you'd like to read more about the contrast between concrete and abstract, see Gideon Rosen's article in the Stanford Encyclopedia on abstract objects.

  • something which might in principle exist by itself. It doesn't logically depend for its existence upon other things. (Contrast holes, shadows, and pains. These seem to depend for their existence upon other objects.)

Substances don't always have to be solid things; they don't have to be things that you can touch and feel. A cloud is a substance. A campfire is a substance. If there are any ghosts flitting about the campfire, then they would be substances, just like knives and campfires. Unlike those other things, though, ghosts would be non-physical substances.

When the dualist says that there are two kinds of things in the world, what she means is that there are two kinds of substances. She's saying that some substances are physical, and other substances, souls, are non-physical. And that it's the non-physical substances that really do all the thinking and feeling. (The dualist need not take any specific stand about numbers, properties, or anything else that's not a substance.)

The materialist, on the other hand, thinks that the world only contains physical substances.

Comment: Some materialists think that this is a ¥¥necessary truth: that it's not even possible for the world to contain non-physical substances of the sort the dualist believes in. Other materialists think it's just a ¥¥contingent truth: the world could have contained non-physical souls, but as a matter of fact, it doesn't. As a matter of fact, the only substances the world contains are all physical ones. Both of these count as materialist views.

Now what will a materialist say about "the mind"? Some materialists say that the mind is just the brain. When ordinary people talk about souls, he thinks, they usually just mean to be talking about the mind, and on his view that's just the brain. Not some non-physical thing like the dualist has in mind.

So that's one way to be a materialist. You say that the mind is not a non-physical substance, a soul, but rather that it's a physical substance, the brain.

But other materialists are more subtle. They say that "the mind" is not really a substance at all--neither a physical substance nor a non-physical substance.

Let's build up to that view gradually.

First consider the following examples.

Claire has a sharp knife. Claire has a sharp wit.
Once you climb the steep cliffs on this side, you'll find a gentle slope down to the plain. Despite his harsh words, Mike has a gentle touch.

Look first at the first column. It says that there is this thing, a knife, that Claire possesses. And there is a thing, a slope, on the other side of the cliff.

But now in the second column, when we talk about a sharp wit and a gentle touch, we don't seem to be talking about things in the same robust and full-blooded way. In one sense a sharp with and a gentle touch are "things" we can talk about. I can say, "There's one thing I really like about her, that's her sharp wit." But Claire's wit doesn't seem to be a thing in the same way that a knife and a slope are things. Knives and slopes are substances, but wits and touches aren't. It would be possible for a knife or a slope to exist, all by itself, floating in space. It wouldn't be possible for a wit to exist all by itself in the same way. (At a minimum, there would also have to exist a person whose wit it was.)

Here's another example. Suppose you tell me, "We're going to take a hike." Wouldn't it be absurd if I responded, "Don't take the last one! I was saving it for this weekend!" Why would that be absurd? It's because a hike isn't really a substance. Rather, it's more a process or activity. It's something that people do, not a thing that people can "take" in the way they can take a ticket.

What do hikes, wits, and touches all have in common? They have it in common that we use nouns to talk about them, but we don't really think there are any substances or things, in the full-blooded sense, corresponding to those nouns. On a hike, the only substances are:

  • the hikers
  • their clothes
  • the dirt path they're walking on
  • the oxygen they're breathing
  • the sweat on their skin

There's not some further, additional substance, the hike.

Now let's consider two more examples:

Claire has a sharp knife. Claire has a sharp wit. Claire has a sharp mind.
Once you climb the steep cliffs on this side, you'll find a gentle slope down to the plain. Despite his harsh words, Mike has a gentle touch. Mike has a gentle spirit.

How do the examples in the third column work?

Remember, the dualist says that the mind is a kind of substance, a special kind of non-physical substance. We saw that one way to be a materialist is to say that the mind is rather a physical thing or substance, like the brain. But maybe the best thing to say is that talk of "having a sharp mind" or "a gentle spirit" is like talk of hikes, wits, and touches. There's not really some additional thing or substance corresponding to these words. Of course there are substances, like rocks and so on. This view says those substances are all physical. When we talk about "a person's mind," though, we're not referring to any substance. Neither a physical substance nor a non-physical substance. To say that a person "has a mind" is just to say that the person's brain and body can do certain things. They can think, they can have experiences, they can make choices, and so on. In the same way, to say that a person is "taking a hike" is just to say that the person is doing certain things. We're not really saying there's some substance, a hike, that the person is taking. It's just a way of talking.

I will count this view of the mind as a materialist view, too, because it says that the only substances there are are material or physical substances. Like tables and rocks and human brains and bodies. There aren't any extra, non-physical substances in addition to all that.

I said that for the materialist, to say that you have a mind is just to say that your brain and body can do certain things. They can think, they can have experiences, they can make choices, and so on.

The dualist doesn't think that brains and bodies can do any of those things. According to the dualist, it's only souls which are able to think, have experiences, and so on. Physical things like your brain and your body can't think and have experiences. Imagine there are all these chunks of dead, unfeeling matter. According to the dualist, it's only after a soul comes along and "animates" the matter, that there can be real thoughts and feelings. Without a soul, there is no thinking or consciousness or any sort of mental life going on.

There are some things that the dualist and the materialist agree on. They agree that there are ¥¥these special kinds of states and processes that only thinking, feeling creatures can have. Some examples are:

  • pains
  • itches
  • the experience of seeing red
  • hearing yourself think
  • wanting to go on vacation
  • remembering that Henry VIII was an English king
  • remembering your first kiss
  • believing that Harvard is located in Massachusetts
  • emotions
  • intending to do the laundry tomorrow

and so on.

The materialist and the dualist agree that only certain sorts of creatures are able to have thoughts, experiences, and other mental states. Whenever a creature is able to have these mental states, we say that the creature "has a mind." So if you have a belief, or experience any emotions, or have memories, then you "have a mind," on everyone's view. Both the dualist and the materialist agree that we "have minds." Having a mind is what distinguishes you from things like rocks and plants. You can think, and you are conscious. But a rock and a plant aren't conscious, and can't think. They don't have any mental life. They don't have minds.

What the dualist and the materialist disagree about is what "having a mind" amounts to. The dualist thinks that in order to have a mind, you quite literally have to have some thing, a soul, connected to your body. The soul is what really does the thinking and feeling. If you have a toothache, it's really your soul that feels it. If you think about Maine, it's really your soul that does the thinking. "Having a mind" is having one of these non-physical things, a soul.

According to the materialist, though, that's not what "having a mind" consists in. According to the materialist, all there is to people is their physical body, their brain, the electrical patterns in their brain, and so on. If you put these together in the right way, the materialist thinks, you'll get beliefs, and emotions, and memories, and so on. The brain and the body are able to have thoughts and experiences all by themselves, because of the complicated way that they're built, without any help from a non-physical soul. The only substances involved are your physical brain and body. When they are configured in the right way, thoughts and feelings take place, and then we say that you "have a mind."


Last Modified: 
Copyright © The President and Fellows of Harvard College