道德規範乃是無條件的行為規範。在理想中，它也應該能夠獨立於主觀目的，給予理性的行為指引。同時，只有道德具有這種特殊的地位。然而，社會上既存的道德規範，是否已經具有這個獨一無二的地位呢？卻一直是道德哲學家爭論的問題。康德的定言令式學說，對這個問題採取肯定的立場，成為理性主義的代表性學說。1972年，芙德站在休姆式理論的角度，對定言令式學說提出質疑。她主張，道德規範必須首先符合行為者的某個主觀目的，才能稱得上是理性的行為指引。在這方面，道德與一般的行為規範並無不同。如果其他的規範是假言令式，那麼道德規範也是假言令式。
芙德的假言令式理論，引起許多學者的關注與批評。其中較可注意的批評，乃是站在道德實在論立場，對道德規範的合理性所作的說明。本論文有三項主要工作：
第一，分析芙德的假言令式理論，顯示她如何質疑定言令式學說，並建立假言令式道德系統；
第二，顯示道德實在論者如何批評芙德的休姆式理論。道德實在論者認為，道德規範沒有普遍合理性，但至少在某種人（即有德者）那兒，可以用他的某些（道德）信念來解釋。
第三，以《道德形上學之基礎》（GMS）一書為根據，分析康德自己的定言令式學說。在八○年代之前，尚沒有人能以純正的康德理論，回應芙德的挑戰。時至今日，康德哲學的研究者已經了解，「目的自身之表述」（FH）以及「自律之理念」（FA），正是康德自己對於道德規範的合理性之說明。
休姆式、道德實在論式，以及康德式的理論，乃是當代道德哲學之中，關於道德規範的合理性問題的三大理論。本論文的結論是：康德式的理論，已足以顯示道德規範的普遍合理性。與此相較，休姆式的理論，未能解釋道德動機之中帶有規範性的一面；而道德實在論的說法，又未能充份解決道德冷漠者的難題。這兩種理論，都不妥當。

One traditional view about morality is: moral considerations themselves give an agent reasons for action, independently of his subjective ends. And if there exists any unconditional principle of rationality, that is of morality. Kants doctrine of the categorical imperative (the doctrine of CI) signifies a profonnd defense of this traditional view. But the Humean theory of practical reason helds that all reasons for action depend upon an agent''s subjective ends. In her paper “Morality as a system of Hypothetical Imperalives”, Philippa Foot challenged Kant''s doctrine of CI from the position of the Humean theory. And she argued that the rational authority of moral considerations wholly depends upon our moral desires, If any social norms with this conditional reason-giving force should be labeled “hypothetical imperatives”, so are moral considerations.
Foot''s theory has received many criticisms. One remarkable kind of criticism, that of the moral realists, said that some cognitive mental states, such as moral beliefs, could motivate and explain moral actions, therefore could be the whole reasons for acting morally. The moral realists attacked on the desire/belief model of Humean theory of moral motivations, but didn''t accept Kant''s characteristic claim that all human beings have reasons for acting morally. Because of this, the genuinely interesting problem still remains that whether or not Kant''s own doctrine of CI can meet Foot''s challenge about morality''s universally rational anthority. Ultimately, the essential point in this debate aroused by Foot is the dispute among three theories about moral motivation, the Humean, the Kantian, and of the moral realism.
This essay concerns with the contributions to this CI/HI debate by three theories of moral reasons above. First, I will analyse Foot''s challenge, and point out the focus of the dispute: Foot''s doubt about the motivational power of moral considerations. Second, I will introduce the moral realist''s theory. Admittedly, I don''t wholly understand the metaphysical foundations of the moral realism, But I doubt its claim about the motivational power of moral beliefs, since this claim connot account for our reflective nature. Finally, I give an outline of Kant''s theory of moral motivation, based upon his Groundwork of the Metaphysics of Morals. According to his theory, the moral motivation not only must be universal, but also be authoritative. This could only be the rational nature as an end in itself. Further more, the autonomy of reason shows that our rational beings have the ability to act on the representation of an end in itself. Thus, moral motivation is univeral and normative, and are categorical imperatives. The Humean Theory cannot account for the normative aspect of moral motivation.

目 錄
本論文引用康德著作縮寫表 ⑤
導 論 1
第一章 芙德的挑戰 5
第一節　康德定言令式理論的基本主張 6
第二節　芙德對定言令式之反駁 9
第三節　定言令式理論的錯誤之根源 12
第四節　假言令式道德系統的建立 14
第五節　定言令式／假言令式理論之爭議焦點 17
第二章 兩種行為理由？芙德與赫姆斯的辯論 21
第一節　「為何我應該道德？」──問題分析 21
第二節　赫姆斯的兩種行為理由理論 22
第三節　芙德的回應 25
第四節　這次辯論的總評 27
第三章 菲利普斯對道德令式之絕對性的說明 31
第一節　道德關懷與道德考量的凌越性 32
第二節　道德旨趣的難題 35
第三節　道德關懷與行為理由 37
第四節　「為何我應該道德？」與定言令式的歷史觀察 40
第五節　菲利普斯道德理由之說的總評 42
第四章 麥克道爾的道德實在論對於定言令式的辯護 44
第一節　行為動機的兩種組成方式 45
第二節　麥克道爾的道德動機理論 47
第三節　認知與動機的隔閡問題 50
第四節　假言令式與定言令式 53
第五節　麥克道爾理論之檢討 54
第五章 康德道德哲學中的定言令式 57
第一節　道德判斷的內在主義與康德的論證計劃 58
第二節　客觀必然性與三種令式 60
第三節　定言令式的概念、與普遍法則之表述 63
第四節　理性特徵作為目的自身 67
§5.4.1　令式的主觀動機與客觀動機 67
§5.4.2　「理性特徵是目的自身」的主張 68
§5.4.3　康德對「理性特徵作為目的自身」的論證 70
§5.4.4　實質的道德行為指導 73
第五節　自律是道德最高原則 74
第六節　內在主義與道德情操 75
§5.6.1　康德式的內在主義 75
§5.6.2　道德堅持力的問題 76
第六章 結 論 79
§6.1　康德對芙德的回應 79
§6.2　對道德實在論的康德式回應 81
§6.3　「出於義務」之道德心理學問題 82
參考書目及論文 84

CI/HI debate:
Philippa Foot, 1972,“Morality as a System of Hypothetical Imperatives”, The Philosophical Review, 81(1972), pp.305─16.
1975a,“Is Morality a System of Hypothetical Imperatives? A Reply to Mr.Holmes”, Analysis, 35(1975), pp.53─56.
1975b,“A Reply to Professor Frankena”, reprinted in Foot, Virtues and Vices, pp.174─180.
1978,“Are Moral Considerations Overriding?” in: Foot, Virtues and Vices, pp.181─188.
Becker, Lawrance 1973,“The Finality of Moral Judgements: A Reply to Mrs. Foot”, The Philosophical Review, 82(1973), pp.364─70.
Frankena, William, K., 1974,“The Philosopher''s Attack on Morality”, Philospphy, 49(1974), pp.345─56.
Holmes, Robert, L. 1974,“Is Morality a System of Hypothetical Imperatives?”Analysis 34(1974) pp.96─100.
1976, “Philippa Foot on Hypothetial Imperatives”, Analysis, 36(1976), pp.199─200.
McDowell, John, 1978, “Are Moral Requirements Hypothetical Imperatives?”, Proceedings of Aristotelian Society, suppl. 52(1978). pp.13─28.
Nesbitt, Winston, 1977, “Categorial Imperatives──A Defense”, The Philosophical Review, 86(1977), pp.217─23.
Solomon, William D. 1975, “Moral Reasons”, American Philosophical Quarterly, 12(1975), pp.331─39.
Phillips, D. Z, 1977, “In Search of the Moral‘Must’”, Philosophical Quarterly, 27(1977), pp.140─157.
1979, “Do Moral Considerations Override Others?”, Philosophical Quarterly, 29(1979), pp.247─54.
1992, Interventions in Ethics, (London: Macmillian Press, 1992)
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Cullity, Garrett, & Gaut, Berys, (eds.) Ethics and Practical Reason. (Oxford: Clarenton Press, 1997).
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Frankena, William K. Ethics, (Englewood Cliffs: Prentice─Hall Inc., 1973).
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Gaut, Berys, “The Structure of Practical Reason” in Cullity & Gaut(eds.) Ethics and Practical Reason, (1997), pp.161─188.
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Herman, Barbara, The Practice of Moral Judgement, (Massachusetts: Harrard University Press, 1993).
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 中文翻譯參考著作：
康德《道德底形上學之基礎》 李明輝譯 （臺北：聯經出版公司，民國七十九年）
李明輝 《儒家與康德》 （臺北：聯經出版公司，民國七十九年）