First published in 1997, this volume originated from an article published in Ratio and reapproaches Aristotle in an attempt to define what counts as an irrational action, along with a general account of irrationality based on a large number of specific examples. It begins with Aristotle, and never leaves him far behind. Contemplating akrasia, will, self-knowledge and commensurability, the author demonstrates that we must allow for the possibility of breakdown in cases where someone may fail to do the rational action through weakness of will and that to make sense of akrasia we must be ready to allow for distinct cases.