Moral theory should be simple: the moral theorist attends to ordinary human action to explain what makes some acts right and others wrong, and we need no microscope to observe a human act. Yet no moral theory that is simple captures all of the morally relevant facts.

In a set of vivid examples, stories, and cases Judith Thomson shows just how wide an array of moral considerations bears on all but the simplest of problems. She is a philosophical analyst of the highest caliber who can tease a multitude of implications out of the story of a mere bit of eavesdropping. She is also...