This disconnect is highly topical: research by psychologists and anthropologists alike suggests that we humans may all be "natural Cartesians", with a deeply ingrained belief in the separateness of invisible mind from visible body. But beliefs, however widespread and compelling, can be false. Child psychologists have established that between the ages of three and five we acquire a "theory of mind" that helps us to appreciate that others have their own perspectives, beliefs and reasons for action. The theory is undoubtedly useful to us in our social lives, helping us to make sense of each other's behaviour, but perhaps its main term, the mind, is a misleading construct. This thought points the way to one possible solution of the problem of consciousness: to recognise that we may be trying to find a natural, scientific, explanation for a supernatural, imaginary, entity. Such an effort is surely doomed to fail. This is Humphrey's line of attack. He deploys several beguiling, and sometimes questionable, tactics as he advances, but he is absolutely right to reintroduce the concept of the soul to contemporary discussion of consciousness. This elusive entity still haunts the science — and scientists — of the mind.

The first section of the book asks what consciousness is. Humphrey's answer is that, au fond, it is an illusion: "a magic show that you stage for yourself inside your own head" — on the basis of those looping loops that circle in our brains. I had some difficulties here. With an illusion like this, who needs consciousness? The subjective qualities of the "magic show" look as if they require about as much explanation as the experiences we thought we were having in the first place. Second, Humphrey rests his case partly on an analysis of a phrase that has been much used in discussion of consciousness since Thomas Nagel's famous essay, "What is it like to be a bat?" Humphrey argues when we apply this phrase to our experience — saying that it is always "like something" to be conscious — we imply that our experience somehow gives us evidence of another world: "from the subject's point of view, consciousness appears to be a gateway to a world of as-if entities". Sometimes it probably does — but when I say that the air I breathe on this spring day is like champagne I seem to be saying something much simpler: there is something, not nothing, my experience is like — i.e. champagne — and that's extremely welcome!

At the heart of the book, Humphrey asks what consciousness is for. He gives a delightfully unexpected, teleological, answer, finding its explanation in the "selective advantage" it confers, its contribution to our biological fitness. But whereas most recent theorists have sought to identify skills which are somehow honed by consciousness, Humphrey regards it as essentially "encouraging" rather than "enabling": it evolved, he argues to make life worth living. He suggests that this evolutionary step occurred 300 million years ago, in the primitive reptiles who are our ancestors, allowing them to receive the evolutionary benefits of possessing a core self and relishing "the enchanted world" that only such a self can inhabit. 

Over the course of evolution, most spectacularly in our species, the core self "that feels and does" gave rise to the extended one that "thinks, perceives, remembers, dreams, desires — a veritable factory [...] whose product is a whole person with a life history". This extended self, as we born dualists experience and conceive it, appears to have miraculous properties: inscrutable privacy, radical freedom, and the capacity to create the sensory world. Reflection on these properties, in the light of our agonising knowledge of the body's inevitable death,  gives rise, in Humphrey's view, to the concept of the soul — immaterial, autonomous, persistent, death-defying.