The mind-body problem is the problem of explaining how our mental states, events and processes—like beliefs, actions and thinking—are related to the physical states, events and processes in our bodies. A question of the form, ’how is A related to B? does not by itself pose a philosophical problem. To pose such a problem, there has to be something about A and B which makes the relation between them seem problematic. Many features of mind and body have been cited as responsible for our sense of the problem. Here I will concentrate on two: the fact that mind and body seem to interact causally, and the distinctive features of consciousness. A long tradition in philosophy has held, with René Descartes, that the mind must be a non-bodily entity: a soul or mental substance. This thesis is called ’substance dualism’ (or ’Cartesian dualism’) because it says that there are two kinds of substance in the world, mental and physical or material. One reason for believing this is the belief that the soul, unlike the body, is immortal. Another reason for believing it is that we have free will, and this seems to require that the mind is a non-physical thing, since all physical things are subject to the laws of nature. To say that the mind (or soul) is a mental substance is not to say that the mind is made up of some non-physical kind of stuff or material. The use of the term ’substance’ is rather the traditional philosophical use: a substance is an entity which has properties and persists through change in its properties. A tiger, for instance, is a substance, whereas a hurricane is not. To say that there are mental substances individual minds or souls—is to say that there are objects which are non-material or non-physical, and these objects can exist independently of physical objects, like a person’s body. These objects, if they exist, are not made of non-physical ’stuff’: they are not made of ’stuff’ at all...