Few subjects in modern science have generated more controversy or inspired more research than the study of the brain. For forty years Donald Mackay was at the forefront of this debate, recognized not only as an experimenter on the visual system, but also for the clarity of his thinking about the theoretical framework and presuppositions behind the brain science. This book is based on the author's 1986 Gifford lectures and gives an accessible overview of the brain and its workings. It also does much more than this as each technical discussion becomes a jumping-off point for reflections in the surrounding areas, ranging from machine intelligence to linguistics, from theories of perception to the question of life after death. Though this book is written in a style suited to the non-specialist, professionals will recognize that much of what is here constitutes fresh contributions to current debates in a variety of areas.