Rene Descartes, one of the most influential philosophers ever, thought the mind was like an open book that could be read by the light of reason. So there was nothing that we could not access or examine in our own minds. In fact Descartes argued that consciousness was the mind - there was nothing beyond it. Now we see the mind as a labyrinthine cellar full of bric-a-brac and untapped rooms of which consciousness is merely one - and a small one at that. Barry Smith charts this change and explains some of the contemporary thinking about consciousness.