All of these theories can strike one as strange and most as counter-intuitive. I shall try to make plain presently. For any system, every fact about the whole is a necessary consequence of the nature and relations of the parts. People are made of atoms. Atoms are purely physical objects, with nothing but physical properties and physical relations to one another.
People have mental states.
No statement ascribing a mental predicate can be derived from any set of purely physical descriptions. But first these theses must be clarified. This means that it would not be possible to deduce the quality of someone's conscious experiences from a physical description of him or of anything else. If a physical description of the universe is given, it will always be an additional piece of information, e.g., to note that someone is in pain. All of these theses can be defended, as I will show below, but the first thing to note is that they cannot all be true.