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 all we would see are parts that push and move each other, but nothing that could explain thinking. • Do you agree that we cannot provide a mechanical explanation of 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
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?
Thought Probe: Living in the Matrix • Can you be sure that you’re not in living in a computer simulation such as that portrayed in the movie, The Matrix? • If so, how? • If not, does that mean that you can’t have knowledge of the external world?
“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.”
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. • Cartesian Dualism: mental states are states of an immaterial substance that interacts with the body.
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?
The Conceivability Argument • It’s conceivable for me to exist without having a body. • Whatever is conceivable is possible. • Therefore, it’s possible for me to exist and not have a body. • If it’s possible for me to exist without having a body, then having a body is not essential to me. • Therefore, having a body is not essential to me.
The Conceivability Argument • It’s inconceivable for me to exist without having a mind. • Whatever is inconceivable is impossible. • Therefore, it’s impossible for me to exist and not have a mind. • If it’s impossible for me to exist without having a mind, then having a mind is essential to me. • Therefore, having a mind is essential to me.
Thought Probe: Bodies, Minds, and Death • Descartes claims that when a person ceases to think, they cease to exist. • Those in a permanent vegetative state seem to have lost the ability to think. • Have those “people” ceased to exist?
The Divisibility Argument • If minds are identical to bodies, then whatever is true of minds is true of bodies, and vice versa. • But minds are indivisible and bodies are divisible. • Therefore, minds are not identical to bodies.
The Causal Impotence of the Mental • Descartes believes that our minds affect our bodies, and vice versa. • But how can a non-physical object affect a physical one?
Epiphenomenalism • People have thoughts, feelings, and desires. How are they related to the body? • 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.