It’s common to the point of cliché to hear engaged couples or newlyweds speak about how excited they are to marry their best friend. Others balk, citing the need to maintain friendships outside a marriage, lest one burden one’s spouse with expectations he or she cannot bear, or arguing that there’s no such thing as a “soul mate.” Nonetheless, in his discussion of the indissolubility of marriage in the Summa Contra Gentiles, Thomas Aquinas writes that “there seems to be the greatest friendship between husband and wife, for they are united not only in the act of fleshly union, which produces a certain gentle association even among beasts, but also in the partnership of the whole range of domestic activity.” Friends share life together, and the fact that husbands and wives share their entire lives—not the fact that they have strong feelings for each other—would seem to make them best friends. By examining Aquinas’s understanding of friendship, chiefly in his Commentary on Aristotle’s Nichomachean Ethics, we can gain insight into the connection he makes between strong friendships and strong marriages.

In the Nicomachean Ethics, Aristotle begins his treatment of friendship by arguing that friendship is a good that all must pursue if they seek to live a happy life. And friendship—at least in its perfect form—is not an incidental good that we pursue in order to gain other things, such as wealth and power. Rather, we seek friendship because it is a participation or sharing (communicatio) in the life of another. Friendship, as Aquinas captures it, is an exchange of love that takes place in repeated acts of goodness from one friend to another. Because it is a habitual act of free choice, friendship is a kind of virtue. Thus even when friends are not performing acts of friendship—such as when they are apart or when they are sleeping—they can be said to be friends because they habitually “live together pleasantly and do good for one another.”

But this degree of pleasure and good is not equally present in all forms of friendship. Every act of friendship is an act of love that seeks an object. We are only friends with someone for a reason. Hence Aristotle identifies three kinds of friendship based on the three objects of acts of love, or reasons for friendship: friendship for the good as such, friendship for the pleasurable, and friendship for the useful. To translate these into practical terms, we could think of them as being friends because there is something intrinsically good and delightful about a person, being friends because someone is funny or attractive or thrilling, and being friends because a person can provide something helpful. In the second two, a person loves a friend for what is incidental. They are friends by way of resemblance. Those in the first category, friends for the good, are friends essentially—for what a person is. Therefore, only those who seek friendship for the sake of pursuing the good, and with good people, can know true friendship.

In a virtuous friendship, a virtuous person loves his friend because he is similar to himself. He loves him as another self, and he feels for his friend what he feels for himself. Such a friendship begins with feelings of goodwill, a disposition in favor of someone based on their natural attributes. Goodwill continues in friendship, but it is joined by acts of beneficence and by concord in mind and heart. This is possible because the friends are alike in virtue. Their virtue impels them to make repeated acts of love and, because virtue is a permanent habit, these acts of love become a permanent, lasting friendship.

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The resonances here between a friendship of virtue and a healthy marriage should be apparent, and this is also the case in terms of friendship’s frequency, its cultivation, and the number of people who can compose a friendship. First, because virtuous people are rare, virtuous friendship is rare. As Flannery O’Connor famously wrote, “a good man is hard to find.” Second, virtuous friendship requires time and discernment: a person needs to find out who is virtuous and wants to be a friend. Third, virtuous friendships can be with only one person, for three reasons. First, Aquinas says, the kind of superabundant love present in virtuous friendship is, by nature, designed for one person, as is evident in sexual love. Second, friends are extremely pleasant to one another, and this is difficult to maintain with more than one person. Third, friends become closer with each other by habitual association, but this is hard and can only happen with one person. Friendship, in short, is difficult. It may be natural, but it requires time and effort, and it is infrequent because of its exclusivity and the rarity of virtue.

If, however, one’s friend remains virtuous, the friendship results in a twofold benefit. First, friends enjoy a friendship because they enjoy each other. Each is another self to the other, and each delights in the other. Just as the good man rejoices at the good he performs, so he rejoices in that of his friend. Because he loves the good and because his friend contains the good, the virtuous man loves his friend’s very existence. He wants to live together with him, to share himself with him, and to receive him in turn.

In addition to the joy of living with and knowing a kindred spirit, the virtuous person takes delight in friendship because it helps him to become more virtuous. Because of our natural affection for ourselves, we cannot judge our own actions well. Since we cannot study our own actions, we need to study those of “another self” whom we love as we love ourselves.

Two friends, therefore, love what is good in each other. Through their friendship, they become goods to each other. Each wishes the other good for the other’s sake, not for his own. This mutual love, Aquinas argues, makes friendship something even above a virtue, because “the act of one is not sufficient but the acts of two mutually loving one another must concur.” Friendship, therefore, is not only a matter of pursuing one’s own virtue but of wanting to help one’s friend become better, too. In finding another self, the friend has found a way to work for virtue in more than himself.

If this is the structure of good friendships, let me suggest four ways in which the sharing of life between a husband and wife can make marriage “the greatest friendship.”

1) A good marriage is founded on the good that the spouses perceive in each other. It allows spouses to delight in each other, to rejoice in each other’s good and in the mutual enjoyment of the good that they share.

2) A good marriage begins with feelings of goodwill and attraction, then is joined to beneficence, doing good to each other, and a concord of mind and heart. Marriage entails doing and willing the good for your spouse constantly—even when you don’t feel like it—and making your spouse’s good your own. And marriage requires and enables enough agreement between spouses so they can live together in peace, even if they do not share the same religion, politics, or other convictions.

3) A good marriage can help you become more virtuous. This is both joyful and very difficult. More so than anything else in life, marriage and children show you just how self-centered you are, and they train you to become centered on the good of another. For Christians, marriage is the path to sanctity that God has prepared for the spouses. And sanctity and virtue, as difficult as they are, allow us to flourish and to more perfectly live a life animated by God’s love.

4) A good marriage entails building and sharing a good life with another person—both the diverse goods that we enjoy together in this life and ultimately our enjoyment of goodness itself, life with God in the next. To put it another way, Christian marriage is a shared pilgrimage to life with God in heaven, and that ultimate goal helps spouses keep in perspective the joys and sorrows they experience.

God shows us what his love looks like by how our spouse loves us.


In the Supplement to the Summa Theologiae, compiled by Aquinas’s students from his lectures and writings after his death, Aquinas shows how grace builds upon and expands the friendship of marriage in making the natural union into a sacrament. Aquinas considers the argument that marriage is not a sacrament because the sacraments derive their efficacy from Christ’s Passion, and since marriage involves pleasure, it does not conform us to Christ’s Passion, which was painful. In response to this argument, Aquinas writes: “Although Matrimony is not conformed to Christ’s Passion as regards pain, it is as regards charity, whereby He suffered for the Church who was to be united to Him as His spouse.”

This is one of those moments when Aquinas’s prose is like a prism that refracts a ray of light into an array of colors, or like a doorway into the vast expanse of a Gothic cathedral. Aquinas is saying that in marriage, the spouses give themselves to each other and lay down their lives for each other totally, just as Christ did for us on the cross. It is that total and faithful self-gift that allows marriage to be an image of Christ’s self-gift for the Church.

Three things follow from this. First, the married couple’s own self-gift becomes the path by which they imitate Christ and become Christ-like. Second, in the sacrament of marriage, God gives us his love so that we can love as he does. Third, marriage is also the place in which we should receive God’s love through the self-gift of our spouse. God shows us what his love looks like by how our spouse loves us.

Conceived in this way, it makes sense for someone to say that he has married his best friend. The friendship of husband and wife is founded on an attraction or thrill, but that thrill has roots in the goodness of the other spouse. It should grow into a series of actions that make both spouses better, that cement their delight in each other’s good in a life of mutual beneficence and sacrifice. Empowered by grace, their marriage becomes an icon of God’s love—however imperfectly—and a means of their growth in that love toward its full flowering in the beatific vision. We could add to Aquinas that not only is marriage conformed to Christ’s Passion as regards to charity, but it is also conformed to the Resurrection: it can be healing and transformative, giving joy now and in the life to come.

This article is adapted from a talk given for the Thomistic Institute at Clemson University.

Image by glogoski and licensed via Adobe Stock.