Cognitive semantics has made important empirical findings about human conceptualization. In this paper some findings concerning moral concepts are analyzed and their implications for medical ethics discussed. The key idea is that morality has to do with metaphors and imagination rather than with well-defined concepts and deduction. It is argued that normative medical ethics to be psychologically realistic should take these findings seriously. This means that an “imaginative casuistry” is to be preferred compared to principlism and to other forms of casuistry. Furthermore, the metaphorical character of central principles in medical ethics such as autonomy, utility, justice, and integrity is indicated. Such principles are interpreted as rules of thumb summarizing the collective wisdom concerning prototype cases.