The American philosopher Charles Peirce described our ability to detect the unconscious clues that guide us to correct answers as "an inward light" – "the loftiest of our merely instinctive powers". Leonard Mlodinow agrees, and his well researched and very readable book argues that the new science and technology of brain imaging has begun to open the door on what was hitherto a closed room: our unconscious, or as Mlodinow calls it the "new unconscious", to distinguish it from Freud's view, which he largely rejects. According to Mlodinow, the unconscious is not there as a defence mechanism against inappropriate desires, but is "a gift of evolution that is crucial to our survival as a species". His study reveals how the hidden structures of the unconscious mind influence our view of self and the world, from the taste of beer (yes, price and packaging really do affect how it tastes) to how "branding a child a poor learner will contribute to making the child exactly that". A fascinating insight into our "inner unknown self" and its role in shaping the world we know.