本論文關心的是規範性問題，即「我為什麼應該遵守道德要求？」根據本文分析，這個問題可以被理解成「我有沒有規範理由遵守道德要求？」據此，藉由探索證成道德要求的規範理由何以成立，就能幫助我們答覆規範性問題。審視不同學者對道德要求的看法之後，本文認為道德要求有四個重要特色：規範性、不可逃避性、優先性、可問責性，而且妥善答覆規範性問題的關鍵，即在於解釋道德要求如何具有這四個特色。是故，本文將檢視後設倫理學中三個主流的理由論（情意論、實在論、建構論），審酌它們對規範理由的說明，能否成功解釋上述道德要求的重要特色，以此判斷誰較能提供規範性問題一個令人滿意的答案。
本文在前半部分主張，情意論、實在論、設限的建構論（其中一種版本的建構論）在解釋道德要求的規範性時會遇到以下困難：情意論或者無法解釋道德要求的規範性，或者必須承認自己是不融貫的理論；實在論與設限的建構論的說明則未注意到規範性的重要面向，無法解釋何以行動者願意發自內心、心悅誠服地遵守道德要求，這會讓道德要求變成外在的威壓脅迫。因此在未提出解決方案之前，本文認為這些理由論難以妥善答覆規範性問題。
在後半部分，本文將捍衛柯思嘉的理由論，指出其做為一種徹底的建構論（另一種版本的建構論）有望妥善答覆規範性問題。首先，她的理由論較其他觀點更能成功解釋道德要求的規範性。其次，透過回應史翠對柯思嘉的批評、渥芙對道德要求的質疑，本文指出她的理由論亦可解釋道德要求的不可逃避性與優先性。最後，藉由回答達沃的第二人倫理學提出的挑戰，本文闡述柯思嘉的理由論如何解釋道德要求的可問責性。若本文主張成立，便能顯示柯思嘉的理由論可以成功解釋道德要求的四個重要特色，妥善答覆規範性問題。

This dissertation focuses on the normative question “why should I do what morality requires me to do?”. According to the analysis herein, the above question can also be formulated as “do I have normative reasons to do what morality requires me to do?”. Accordingly, by exploring how normative reasons exist as the justification for moral requirements, we can better answer the normative question. After reviewing the features of moral requirements proposed by different scholars, this dissertation contends that there are four essential features of moral requirements, which are normativity, inescapability, supremacy, and accountability. Moreover, this dissertation also argues that the key to properly answering the normative question is to explain how moral requirements accommodate these four features. To achieve this goal, this dissertation will investigate three mainstream metaethical theories of reasons, i.e., conativism, realism, and constructivism to examine whether they can successfully provide proper space for those important features of moral requirements and thereby to determine which theory of reasons can satisfyingly answer the normative question.
The first half of this dissertation argues that all conativism, realism and restricted constructivism (one version of constructivism) will face difficulties as they try to explain the normativity of moral requirements. Conativism either fails to explain the normativity of moral requirements or fails to be a coherent theory. On the other hand, realism and restricted constructivism pay only limited attention to one important aspect of moral requirements. This makes neither of them be able to spell out why agents are willing to abide by moral requirements conscientiously and sincerely. As a result of this, moral requirements become a kind of external coercion. Therefore, these theories of reasons will have difficulties answering the normative question properly before coming up with ways to meet the above challenges.
The second half of this dissertation argues that, as a thorough constructivism (another version of constructivism), Christine Korsgaard’s theory of reasons is expected to properly answer the normative question. First, compared to other theories, Korsgaard’s theory can better explain the normativity of moral requirements. Second, in response to Sharon Streets’ objection to Korsgaard and Susan Wolf’s suspicion of moral requirements, it will be shown that Korsgaard’s theory can also explain the features of inescapability and the supremacy of moral requirements respectively. Finally, by responding to the challenge from the second-personal morality advocated by Stephen Darwall, this dissertation elaborates on how Korsgaard’s theory explain the accountability of moral requirements. If the arguments of this dissertation are sound, then it shows that Korsgaard’s theory of reasons can better account for the four important features of moral requirements and more properly answer the normative question.