現代倫理學界習慣把後呆論，義務論和德性倫理三者視為立場迅異，互不相容的規範道德理論。對於這種觀點，卡根曾提出一套分析規範道德理論的方法回應。據此法所言，後呆論，義務論和德性倫理其實各自針對不同的問題，原則上可以並行不悴。本文昌在批評比說，並由此旁及規範道德理論的結構問題。文章首部份先簡要說明卡根的理論的基本結構，並嘗試修正當中的漏洞。後半部份將論證其理論為何未能證成「三種道德理論可以兼容」此論語，進而就規範道德理論的區分方法提出意見。

Contemporary normative theories of ethics are often divided into three
categories, namely the consequentialist theories, the deontological theories, and virtue ethics. For many, this trichotomy naturally suggests that the three categories of theories are totally incompatible. Based on his proposal of a new taxonomy of normative ethics, however, Shelly Kagan rejects this very suggestion. His stance is that, in principle, the three ethical theories are completely compatible, only that they address three different concerns in normative ethics. The present paper aims to show
that Kagan’s taxonomy cannot justify the compatible thesis, and to provide some remarks on the structure of normative ethical theory. The paper is divided into two parts. Part I offers a critical introduction to Shelly Kagan’s classification scheme and other related issues. Part II proceeds to argue why the compatible thesis which rest on Kagan’s taxonomy cannot be retained. On the basis of these discussions, the
paper ends with some suggestions on the problem of classification of normative ethical theory.