substance dualism

• substance dualism holds that there are two types of substances, mental substances (mind) and physical substances (bodies).
• substance dualism claims that minds are not bodies, parts of bodies or properties of bodies.
• cartesian substance dualism claims that minds can exist independently of bodies.
• descartes argues that bodies are divisible into spatial parts, but minds have no such parts. therefore, the mind is a distinct substance from the body.
• leibniz's principle of the indiscernibility of identicals claims that if two things are identical then they are just one thing and share all their properties.
• we can object that not everything that is physical is divisible. therefore, showing that the mind isn't divisible doesn't show that it isn't physical.
• we can object that descartes' indivisibility argument assumes that minds exist as substances.
• descartes argues that he has clear and distinct ideas of the mind and body as separate substances, and that god can create whatever descartes has a clear and distinct idea of. Therefore, mind and body can exist as, and therefore are, separate substances.
• descartes describes clear as 'present and accessible to the attentive mind', and distinct as 'if as well as being clear, it is so sharply separated from all other perceptions that it contains within itself only what is clear'. (The example of pain shows that a perception can be clear without being distinct, but cannot be distinct without being clear.)
• we can question whether it is conceivable that the mind can exist without the body, this thought seems confused or uninformed.
• many philosophers distinguish between physical, metaphysical and logical possibility.
• what is physically possible is possible according to the laws of nature as they happen in to be the natural world.
• what is logically possible is anything that is not conceptually self-contradictory.
• what is metaphysically possible is what is logically possible, constrained by the real nature or identity of things. (example: charge of electron could have been higher)
• we can object that descartes is wrong to infer that, because he can conceive of the mind existing without the body, it is metaphysically possible for it to exist without the body. descartes replies that the inference is justified if our conceptions are clear and distinct.
• we can object that not only can we conceive the mind and body as distinct substances, we can also conceive of them as distinct properties of the same substance - both are metaphysical possibilities.
• we cannot infer from how it is metaphysically possible for the mind and body to be to what they are in the actual world.