亞里斯多德指出，人的自然本性要求倫理學的目的在追求善或幸福。多瑪斯依據亞里斯多德的說法，亦主張倫理學的發展與人性有關，因此，他認為「人性行為」即是「倫理行為」。傳統基督宗教的倫理主張亦多半承繼著亞里斯多德至多瑪斯以來的說法，從人心的「訴求」(postulate)開始，肯定人類普遍具有的人性趨向在於以「追求幸福」為目的；並在此基礎脈絡下，將「何謂幸福」課題的探索與「至福－上帝或天主」相連結；當深入觸及「什麼是最終幸福？」這個問題時，便超越倫理學的探討而褣入到形上學「存有」課題中。 此外，多瑪斯和亞里斯多德也都主張，無論是從認知層面認識與分析倫理行為的形成，或者是就倫理學層面瞭解倫理行為實踐的過程，都涉及理智與意志的相互作用。因此在本文中，所使用的方洲乃是從知識層面的探討來掌握其倫理層面的意涵。在知識層面，先了解其「倫理行為」的意涵；其次，分析倫理行為的構成要素：「理智」與「意志」；第三，分析倫理行為實踐的基礎：自然律。在倫理層面，則就理智、意志和自然律三者的關係來探討倫理行為的實踐。說明理智如何依據自然律來認識和判斷，而意志如何依據自然律來抉擇與實踐。

　　　　　It is pointed by Aristotle that human nature requires ethics to purse good or happiness. Following Aristotle, Aquinas also maintains that the development of ethics is connected to human nature; he thus assumes “actus humamus” to be “ethical acts.” The ethical claims of traditional Christianity mostly follow the doctrines of Aristotle and then Aquinas, beginning with the “postulate” of human minds and affirming that the common tendency of mankind is to “purse happiness”; in this basic context, we relate the exploration of “what is happiness” with “the supreme happiness-God or Adonai.” As we delve into the question “what is the ultimate happiness?” we have gone beyond the level of ethics to explore the metaphysical issue of “being.” Besides, both Aquinas and Aristotle advocate that the interaction between reason and will is involved weather we cognize and analyze the formation of ethical acts through the cognitive dimension or we understand the process of ethical acts through the ethical dimension. Therefore, in this article, we first grasp the significance on the dimension of ethics through the exploration on the dimension of knowledge. On the dimension of knowledge, we first understand the significance of “ethical acts”' then we analyze the constituent elements of ethical practice-”reason” and “will”; and finally, we analyze the basis of ethical practice: natural laws. On the ethical dimension, we approach the ethic acts and practice in terms of reason, will, and natural laws to explain how reason cognizes and judges according to natural laws and how will chooses and practices in terms of natural laws.