有關行動理由的哲學爭辯常聚焦於理由與動機之關連，內在論主張行動理由與動機事實有必要之聯結，外在論則否認。1980 年，威廉斯發表論文“Internal and External Reasons”，提出反對外在論的強力論證，引發了倫理學、行動理論以及理由理論一連串深具影響力的辯論。二十年後，他發表“Some Further Notes on Internal and External Reasons”（2001），精進他的休謨理論以回應這些年來其他學者所提出的質詢；更重要的是，他將過去二十多年來的主要批評歸類為兩種進路：「康德進路」以及「亞理斯多德進路」，並且對二者提出強烈反對。本文檢視康德進路及亞理斯多德進路近來的可能發展，其中包括柯思嘉和麥克道爾的哲學論述，以解釋並論證為何威廉斯的最新論點不足以反駁此二進路。

A central issue in the contemporary philosophy of action focuses on the relation between reason and motivation: Internalism holds, while Externalism denies, that there is a necessary connection between reasons for action and motivational states. In 1980, Bernard Williams launched a powerful argument against Externalism in his article, “Internal and External Reasons,” which triggered influential debates in ethics, action theory, and theory of reason.Twenty years later Williams published “Some Further Notes on Internal and External Reasons” (2001), in which he refined his Humean theory so as to accommodate the many criticisms he had so far received. More importantly,he classified his major critics, in the past two decades, mainly into two groups,“the Kantian” and “the Aristotelian,” and raised objections to both. This paper explores the later development of the Kantian and the Aristotelian approaches,primarily in terms of the recent works of Christine Korsgaard and John McDowell,and argues to the effect that Williams’ objections are insufficient to refute the two approaches.