Consciousness is, in one way, the easiest and most obvious thing in the world to understand, for anyone capable of thinking about it is intimately conscious of being conscious – we live with our noses pressed hard up against our own consciousness, which attends every moment of our aware experience and thought; and similarly, the consciousness of others is lambent in their faces and behaviour, and we each have a rich and highly nuanced knowledge of how to read and respond to those lambencies. Their presence and our understanding of them constitute the ordinary stuff of everyday social interaction.

At the same time, consciousness is by far the most perplexing mystery facing philosophy and the neurological sciences. It is such a difficult problem that for a long time philosophers put off thinking about it, and scientists ignored it entirely. Some, in the tradition of Descartes, still think that it