The relation between body and mind is one of the oldest riddles that has puzzled mankind. That material and mental events may interact is accepted even by the law: our mental capacity to concentrate on the task can be seriously reduced by drugs. Physical and chemical processes may act upon the mind; and when we are writing a difficult letter, our mind acts upon our body and, through a chain of physical events, upon the mind of the recipient of the letter. This is what the authors of this book call the 'interaction of mental and physical events'. We know very little about this interaction; and...