少子化時代，學校教師普遍反應獨生子女的人際相處能力有待提升。近年蓬勃發展的幸福研究顯示，正向人際關係與交友是影響幸福的關鍵要素。除此科學觀點外，本文擬就Aristotle觀點下友愛／友誼之於幸福人生的關係做探討，闡明友誼的形成要素與類型，進而探究理想的友誼類型—德行之交如何做到適當地愛人。本文針對友愛／友誼與幸福人生的關係，提出善用朋友作為行德資源的「工具說」、朋友提供必要的修德沃土與行德良機的「脈絡說」，以及友愛之德使我們變成真正朋友的「內在善說」。友愛之德是透過後天教養與主動修養下，個體學習在真實自愛的基礎上，愛品格之友如同另一個自我，關照彼此理性與德行發展，繼而變成一個真正的朋友。這體現在選擇有德的好人結交為友，在共同生活下一起行德與對話，繼而相互「造就」彼此變成更好的人。

In the age of a low birth rate, an increasing number of schoolteachers claim that the only child’s competency in interpersonal interactions remains to be improved. Rapidly growing research on happiness shows that positive relationships and friendship are vital to personal flourishing. This study investigates the role of friendship in human flourishing. The study analyses the formative elements and types of friendship and illustrates how the two parties of the ideal type of friendship, namely friendship of virtue, love each other properly. Friendship is indispensable to human flourishing in the following ways: first, friends can serve as valuable resources and useful instruments for virtuous activities; second, friends provide the fertile land in which virtues are nurtured and the primary objects towards which the cultivated virtues are exhibited; third, in addition to being an external good, the virtue of friendship is an intrinsic good, indicating that its possessor has become a true friend. Friendship as a moral virtue is not inborn but cultivated through good habituation and active self-cultivation. On the basis of true self-love, the (not yet fully) virtuous person learns to love his/her friend as another self, developing one’s friend’s reason and virtues. In doing so, the virtuous person gradually becomes a true (virtuous) friend. Virtuous friendship is incarnated when choosing good persons as friends and spending time together performing virtuous actions and having intimate conversations, thereby “making” each other a better person.