Human beings have bodies. These are physical things made of matter. We have no special worries about how they fit into the natural world described by science. Our bodies would fall under the general problem of characterizing matter, although we may feel that we would have to investigate biology if we wanted to understand living matter in detail.

As well as bodies, however, it seems apparent that we also have minds. These have some very special abilities. I can think thoughts, which are private and may remain so. I can have beliefs and knowledge. As we saw in Chapter 7, I can feel sensations. I can feel pain, see colours and hear sounds. Such sensations exist, if they exist anywhere, in my mind. Other people may look at the same patch of red and experience their own sensation of red. Although there is a perfectly respectable sense in which we see the same thing, there is also a tempting thought that I see only my own sensation of red and you see only your own sensation of red. Sensations are part of a wider phenomenon that we attribute to mind: consciousness. This will include sensations, perceptions, thoughts, dreams, imagination, after-images and so on. It is a kind of general awareness of the world and of the state of my own mind that purely physical things, such as rocks and chairs, do not have.