Chapter 2The Mind-Body Problem

Bodies and Minds

• Modern science has shown that what goes on in our bodies can be explained in physical terms, as the result of various electrochemical or biomechanical interactions.

• But what about what goes on in our minds? Can our thoughts be explained physically?

Thought Experiment: Descartes’s Mechanical Moron

• Can we construct a machine that thinks?• Descartes claims that no machine would be

able to use language or solve problems like we do.

• Do you agree? Why or why not?

Thought Experiment: Leibniz’s Mental Mill

• Suppose that we created a machine that thinks, and suppose further that we were able to walk around inside the machine.

• Leibniz claims that explaining the working of the parts of the machine would not explain its thinking.

Thought Probe: Walking Around Inside the Brain

• Suppose you were able to walk around inside a brain, like the crew from the movie Fantastic Voyage.

• Would you observe thinking?

Theories of Reality

• Idealism: the doctrine that all that exists are minds and their contents.

• Materialism: the doctrine that all that exists are material objects.

• Dualism: the doctrine that reality contains both mental and material things.

Section 2.1The Ghost in the Machine

Mind as Soul

Cartesian Dualism

• Cartesian dualism is the doctrine that mental states are states of an immaterial substance that interacts with the body.

Descartes’s Doubt

• We know something only if it’s certain.• Most of what we think we know is based on

sense experience.• But we can’t be certain of anything we’ve

learned through sense experience.

Thought Experiment: Descartes’s Dream Argument

• “How often has it happened to me that in the night I dreamt that I found myself in this particular place…while in reality I was lying undressed in bed.”

• Can you be certain that you’re not dreaming right now? If so, how?

Thought Experiment: Descartes’s Evil Demon

• “How do I know that [an evil demon] has not brought it to pass that there is no earth, no heaven, no extended body, no magnitude, no place, and that nevertheless they seem to me to exist just exactly as I now see them?”

• Can you be certain that there is no such demon?

“I think, therefore I am”

• Descartes cannot doubt that he is thinking, for doubting is a type of thinking.

• And Descartes can’t doubt anything unless he exists.

• So Descartes claims that he can be absolutely certain of one thing, namely, “I think, therefore I am.”

The Conceivability Argument

1. It’s conceivable for me to exist without having a body.

2. Whatever is conceivable is possible.3. Therefore, it’s possible for me to exist and not

have a body.4. If it’s possible for me to exist without having a

body, then having a body is not essential to me.5. Therefore, having a body is not essential to me.

The Conceivability Argument

6. It’s inconceivable for me to exist without having a mind.

7. Whatever is inconceivable is impossible.8. Therefore, it’s impossible for me to exist and not

have a mind.9. If it’s impossible for me to exist without having a

mind, then having a mind is essential to me.10. Therefore, having a mind is essential to me.

Cartesian Dualism

• Descartes has proven that he is a thing that thinks.

• But physical things, he claims, cannot think.• So, he concludes, he (his mind) is a non-

physical thing.

Thought Probe:Animal Soul

• Descartes believed that only humans had souls because, among other things, only humans have free will.

• Do you agree? Do animals have souls?

Indiscernibility of Identicals

• The indiscernibility of identicals is the principle that if two things are identical, then they must both possess the same properties.

• For example, if Mark Twain is identical to Samuel Clemens, then whatever is true of Mark Twain is true of Samuel Clemens and vice-versa.

The Divisibility Argument

1. If minds are identical to bodies, then whatever is true of minds is true of bodies, and vice versa.

2. But minds are indivisible and bodies are divisible.

3. Therefore, minds are not identical to bodies.

The Problem of Interaction

• Descartes believes that our minds affect our bodies, and vice versa.

• But how can a non-physical object affect a physical one?

Parallelism

• One way to deal with the problem of interaction is to say that the mind and body only seem to interact with each other.

• According to parallelism, mental processes and physical processes run parallel to each other. There is a correlation between mental and physical events, but no causal interaction.

Occasionalism and the Preestablished Harmony

• Occasionalism is the parallelist theory of the mind that claims the correlation between mental and physical events is produced on each occasion by God.

• Preestablished harmony is the parallelist theory of mind that claims that the correlation between mental and physical events was established by God at the beginning of the universe.

The Causal Closure of the Physical

• Descartes’ dualistic interactionism runs afoul of a basic principle of materialism known as the “causal closure of the physical.”

• According to this principle, everything can be explained in purely physical terms.

• Nevertheless, people do have thoughts, feelings, and desires, and these things seem to be nonphysical.

• How can we reconcile these facts?

Epiphenomenalism

• Maybe we can reconcile them by admitting the existence of Cartesian minds and denying them any causal power.

• According to epiphenomenalism, the mind is an ineffective by-product of physical processes; the body affects the mind, but the mind does not affect the body.

The Problem of Other Minds

• Because Cartesian minds have no physical properties, they cannot be sensed or detected by any physical instruments.

• If so, Descartes cannot know that other people have minds.

Solipsism

• The only mind that we can know for certain exists is our own.

• Some have made the further claim that the only mind that exists is their own. This is known as solipsism.