亞里斯多德定義幸福為「一種靈魂遵循完滿德行之實現活動」。多數的人會同意幸福為人類行為的最終目的，但對於快樂是否為此項最終目的一項要素卻有著不同的看法。在哲學史上，些許專家在討論倫理學時反對將人類對於快樂的追求視為一項合理的欲求，對此，亞里斯多德卻採相反的看法。在《尼各馬科倫理學》裡頭，隱含著一項對於快樂之分辨的判斷標準，亞里斯多德藉此區分出那些快樂是好的、那些快樂是壞的。此項標準的建立，使得人們對於快樂的欲求具有合理性，從而由此標準所篩選出的快樂有助使我們的實現活動更為完滿。

　　　　　Aristotle defined eudaimonia as “a kind of activity of the soul in accordance with complete virtue.” Most people would agree that eduaimonia is the final goal of our behavior. Now we have a question about eduaimonia of which pleasure is an element. In the history of philosophy, we can find many philosophers who refused to see human beings' pursuit of pleasure as a reasonable desire. But Aristotle took a different attitude; he argued that pleasure itself was perfect and complete, and it helped completing every engergeia as well. Aristotle provided us with a standard that is implicated in Nicomachean Ethics to distinguish between good and bad pleasures. I will explain what the standard is and show why Aristotle thought that people's desire for pleasure was reasonable.