The goal of criminal law is to foster morality and to discourage criminal behavior. Therefore, it is important for prospective criminals to understand what it is about justification and excuse that changes crimes to noncrimes. The defense of justification is applied when acts are carried out to prevent or redress harm. Excuse, on the other hand, is a defense that asserts the actor's mental inability to consciously do evil. The article discusses the historical evolution of legal exculpation, noting the emphasis on excuse in the last century. The article argues that a transactional analysis of exculpation is more accurate than the more traditional comparative-harm analysis proposed by Professor Greenawalt. 79 footnotes.