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THE unconscious is not what it used to be. Modern science has transformed our understanding of what, for Freud, was a repository of repressed desires. He saw the unconscious, as described in a much-cited 1992 study, as seething with 鈥渓ust and anger鈥� hallucinatory, primitive, and irrational鈥� (American Psychologist, vol 47, p 788). Thanks to recent work across psychology, neuroscience and other disciplines, we now see it as a powerful, efficient decision-maker critical to our survival.

鈥淲e now see the unconscious as a powerful, efficient decision-maker critical to our survival鈥�

There are two ways of dealing with the 鈥渘ew unconscious鈥�. One is to fret over its implications for free will. How can we be rational agents when we are not even aware of our boundless unawareness? The other is to celebrate and marvel at the many ways it serves us. This is the approach physicist and author Leonard Mlodinow takes in Subliminal, which makes what could have been a sobering look at the unconscious an entertaining and uplifting one.

Mlodinow runs through study after study and some engrossing real-life examples to reveal how subliminal processing controls our sensory systems, creates and distorts memories and guides our intuitions about people. He shows how it can lead us to unfortunate stereotypes and unwise voting choices, guide our emotions and delude us into believing we know why we feel the way we do. He is pragmatic about how completely it leads us astray and the near-impossibility of overriding it, but he is not going to let that spoil the journey, acknowledging how lost he would be without it.

Mlodinow makes much in the prologue of how this new knowledge was made possible by 鈥渟ophisticated new technologies鈥�, in particular functional magnetic resonance imaging. Yet fMRI barely features in the rest of the book: the examples he uses are almost exclusively from social or cognitive psychology.

Neuroscience will no doubt teach us much about how brain states relate to behaviours, thoughts and feelings, but the idea that it is responsible for our modern understanding of the mind is a little fantastical.