What is Substance Dualism?
1) One traditional definition of a substance is something that doesn't depend on any other thing to exist.
2) Substance dualism holds that there are two types of substances, each capable of existing without the other:
- Mental substances (minds)
- Material substances (bodies)
3) Materialism holds that there are only material substances, so that everything that exists is - or depends on - a material substance to exist.
1) Plato argues that - unlike the body - the soul cannot be destroyed because it does not have parts. We can reply that there can be other kinds of destruction.
2) He also argues that all change involves something coming from its opposite. Becoming alive is a change from not being alive. It is the joining of the soul to the body; so the soul must exist before life. We can reply that 'coming into existence' doesn't invlove one's changing from one thing to another.
Descartes' Knowledge Argument
1) Descartes argues that he can doubt the existence of his body, but not that of his mind, which shows that his mind can exist without his body.
2) We can object that he has not shown he/his mind exists as a substance, a unitary thing. He could be no more than a succession of thoughts,
3) Another objection is that we cannot legitimately infer from conceiving of the mind existing without the body that it can actually exist without the body. Being able to conceive of two things as different doesn't guarentee that they are two different things, rather than one thing thought of in different ways.
4) Descartes argues that having parts is an essential property of bodies, as things that exist in space. But the essential property of minds is thought; and minds have no parts. Therefore, minds and bodies are distinct.
5) We can object that this presupposes that minds exist (so as to have properties).
Problems associated with this view of mind
1) Substance dualism entails that we are two things, mind and body, connected together. We can object that our experience is of being just one thing. (The Mind-Body Problem)
2)Neuroscience has shown that the mind is very dependent on the brain, which underminds the idea that the mind is a seperate substance. Descartes can respond that the dependence is causal, not logical.
3)Substance dualism faces the problem of explaining how the mind, given that it is so different from the body, can cause physical events.
4) Descartes assumes we can make sense of the idea of our minds existing alone, without any other mind or physical world. This entails that words must get their meaning by referring to our ideas, thoughts and sensations. But if this is true, the word 'experience' means my experience. Since it is logically impossible that anyone else should hve my experience, it is logically impossible that anyone else should have experience, This is solipsism.
5) Substance dualism also faces the challenge of showing that we can know other minds exist. If minds are logically independent of bodies, any evidence from someone's bodily behaviour does not prove they have a mind.
Responses to these problems
1) The argument from analogy claims that I can infer other people have minds because they behave as I do, and I have a mind.
2) The argument from inference to the best explanation claims that the hypothesis that other people have minds is the best explanation for their behaviour. We can develop this by saying that mental states are defined by their causal relations.
3) We can object, first, that this account of mental states is false,