This book should become a classic in the study of philosophy and psychiatry. The lucidity of the writing makes it, at once, profound and accessible. While acknowledging the substantial contribution of the biological sciences to our understanding of unusual mental states, Glover explores in depth how far an observer can make sense of or interpret them. The implications for how we might think about values, identity, agency, the boundaries of illness, and treatment are most richly drawn.--George Szmukler, King's College London"