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Swinburne criticises hard and soft materialism :
The first view, which I shall call 'hard materialism', claims that the only substances are material objects, and persons (including humans) are such substances. A person is the same thing as his body (and his brain is the same thing as his mind). The only events which occur are physical events, viz, ones which consist in the instantiation of physical properties in material objects. There are no mental events in the sense in which I have analysed this notion; for there are no events distinct from physical events to which the subject has privileged access. Hard materialism seems to me obviously false. There really are events which humans experience and which in consequence they can know about better than does anyone else who studies their behaviour or inspects their brain. My sensations, for example - my having a red after-image or a smell of roast beef - are such that I have an additional way of knowing about them other than those available to the best student of my behaviour or brain; I actually experience them. Consequently they must be distinct from brain events, or any other bodily events. A neurophysiologist cannot observe the quality of the colour in my visual field, or the pungency of the smell of roast beef which I smell. A Martian who came to Earth and captured a human being and inspected his brain, could discover everything that was happening in that brain but would still wonder whether a human really feel anything when his toe is stamped upon. There must be mental events in addition to physical events.
The second view in the history of thought about the mind/body problem is the view which I shall call 'soft materialism'. It is often called 'property dualism'. Soft materialism agrees with hard materialism that the only substances are material objects, but it claims that some of these (that is, persons) have mental properties which are distinct from physical properties. Brain-events certainly often cause mental events and vice versa. Neurones firing in certain patterns cause me to have a red after-image. And - in the other direction - trying to move my arm causes the brain-events which cause my arm to move. These are causal relations between distinct events - just as the ignition of gunpowder is a distinct event from the explosion which it causes.
The basic difficulty, however, with soft materialism as with hard materialism, is that there seem to be more truths about the world than the doctrine says that there can be. Hard materialism says that you have told the whole story of the world when you have said which material objects exist and which physical properties they have. But, as we have seen, there is also the issue of which mental properties are instantiated. Soft materialism says that you have told the whole story of the world when you have said which material objects exist and which properties (mental and physical) they have. However, full information of this kind would still leave you ignorant of whether some person continued to exist or not. Knowledge of what happens to bodies and their parts will not show you for certain what happens to persons. I have tried to illustrate this with the example of brain transplants.