There seem to be two very different kinds of things going on in the world: the things thatbelong to physical reality, which many different people can observe from the outside, andthose other things that belong to mental reality, which each of us experiences from theinside in his own case. This isn't true only of human beings: dogs and cats and horses andbirds seem to be conscious, and fish and ants and beetles probably are too. Who knowswhere it stops