The Secunda pars is subdivided into two sections: the Prima secundae and the Secunda secundae. The Secunda secundae moves from the general moral principles to what might be called Christian moral living. It examines in greater detail concepts introduced in the Prima pars, namely the “cardinal virtues” of prudence, justice, temperance, and fortitude, which are relevant to all humans. Then Thomas moves to those virtues specific to the Christian life, namely the “theological virtues”  of faith, hope, and charity. Charity, for Thomas, is the central notion to the development of his argument in the Secunda secundae, because “it is the form of all the virtues” (IIa IIae q. 23, a.8). Thus, it is within charity that people attain to their proper end (Beatitudo). Therefore, charity is the greatest of all the virtues because its end is supernatural; in that, through it we come to love God for himself and also love that which God loves (IIa IIae q. 23, a.6; q. 25, a.1).
Question IIa IIae q. 23 a. 1 examines the nature of charity and raises the question as to whether charity constitutes friendship (amicitia). Thomas answers that, yes, charity is friendship, insofar as charity is a love which is benevolent as regards its object. Following Aristotle, Thomas defines friendship as love for someone so as to wish good for them, rather than for ourselves. This stands in contrast to concupiscence which “loves” an object merely as it relates to the subject (e.g. a person’s love of wine). For Thomas, the idea that one could love wine of itself is absurd. To say that one loves wine is merely to say that one loves what is induced in the subject as a result of the wine. Charity, however, entails some sort of communicative relationship between subjects in which there is a mutual sense of benevolence. In this sense, friendship is only available between rational agents. Accordingly, because God communicates the benevolent gift of himself to humanity, through our fellowship with Christ, this communication constitutes friendship. Thus, charity is the friendship between God and humanity. This point is seconded by the sed contra statement, which quotes John 15:15: “I will not now call you servants…but My friends.” The sed contra indicates that this was said to the disciples for no other reason than charity, presumably because the argument seems to assume that Jesus had no “need” of friends. It may be concluded thus—at least in so far as the argument is concerned—that charity is friendship.
Preliminary Argument 1 contends that charity is not friendship. Based upon a quote from Aristotle, the interlocutor concludes that friends tend to dwell with each other. However, when placed in conversation with Dan. 2:11, which says that, “[God’s] dwelling is not with men,” it would seem that this would preclude the possibility of charity being friendship between human beings and God. In response, Thomas replies that human beings are not unidimensional, but are rather composite, possessing both corporeal and spiritual natures. With respect to our corporeal/sensitive nature humans cannot be said to have fellowship with the Divine. However, with respect to our spiritual life, as a result of our rational nature, human beings can be said to have fellowship with both God and angels. While in this life such fellowship is necessarily limited, Thomas believed that in heaven the saints would possess perfect charity.
Preliminary Argument 2 contends, based upon a quote from Aristotle, that “there is no friendship without return of love.” However, when placed in conversation with Jesus’s command in Matt. 5:44 to “Love your enemies,” it becomes difficult to maintain that charity could be said to constitute friendship. This is because, according to this argument, if love is not reciprocated by the individual receiving the love it is not truly friendship. In response, Thomas replies that friendship may extend to a person in two ways: first, to the person directly and secondarily—as a consequence of the former—to any individuals associated with that person (e.g. any friend of x is a friend of mine). Thomas seems to assume that friendship extends necessarily and absolutely to individuals by association, even if they happen to hate us. While we may not be as inclined to call such individuals “friends” as perhaps Thomas was, the notion that we may be inclined to a degree of obligation towards such individuals as a result of our mutual relationship is not farfetched. From this assumption, Thomas moves to conclude that charity can be said to constitute friendship with one’s enemies—not in so far as they are our enemies—but in so far as they are God’s children. Thus, we have friendship with God directly and we are therefore able to have charity for even our enemies for God’s sake.
Preliminary Argument 3 explicates the 2nd Argument by use of Aristotle’s 3 categories of friendship: directed respectively towards the useful, the delightful, and the virtuous. The useful friendship is the one possessed for its utility. The delightful friendship is maintained for the pleasure it brings. However, both of these forms are superficial and cannot relate to true friendship which St. Jerome indicated was based upon fear of God and the study of the Divine Scriptures. Neither can charity be the virtuous form of friendship, because through charity we love our enemies and that is not the function of friendship. According to Aristotle, the virtuous friendship can only be had between virtuous men. Therefore, charity cannot be friendship. In response, Thomas refers to his contention that to love someone is to love those in relationship with them. He concludes that the friendship is directed to the virtuous person, but extends to those in relationship to him, regardless as to whether or not the individuals themselves are virtuous. In charity we love for God’s sake.
 The second treatise or major division of the Summa theologae.
 The first of two divisions of the secundae pars or the ‘Treatise on Ethics,’ which has to do with ethics in general (i.e. the foundations of ethics).
 ST I-II.Q. 61. see also , Plato, Protagoras 330b; Wisdom of Solomon 8:7; Augustine, De Civitate Dei IV, 20, et al.
 ST I-II. Q. 62; 1 Cor. 13:13
 Nicomachean Ethics. viii 2, 3
 Nicomachean Ethics. viii 5
 Phil. 3:20
 Apoc. 22:3, 4
 Nicomachean Ethics. viii 3
 See M. Friedman, "The Practice of Partiality." Ethics, 7 1991: 818-835. See also S. Scheffler, "Relationships and Responsibilities." Philosophy and Public Affairs, 1997, Summer: 189-209.