The implication of this fact may startle us: in erotic love, man loves not only for the sake of the beloved, but for his own sake, too. We are accustomed to thinking of authentic love as an affirmation of the beloved’s good at the expense of our own, to giving without counting the cost, loving without an eye for our own desires and fulfillment. Yet the longing for self-fulfillment with another is constitutive of the human condition. As St. Thomas Aquinas repeatedly said, we cannot choose not to pursue our own happiness; this holds true even in our most altruistic and charitable moments. We are, as then-Cardinal Joseph Ratzinger explained in a 1991 speech, ontologically oriented toward and attuned to the pursuit of the transcendent goods of truth, goodness and beauty. All of our loves are “for our own sake.”

Eros is not purely self-referential or self-seeking, however: it does not seek to instrumentalize the other for the self’s sake. In erotic love, Pieper observes, we say to the beloved, “It’s good that you exist—good not just for you, nor just for me, but for us.” In eros, we find ourselves enchanted by another to the extent that, without much effort, we truly love another as we love ourselves. For many of us, the first time we woke up in the morning and regularly thought about someone other than ourselves was when we were first in love, or in eros. We all have seen how spontaneously and effortlessly we can appreciate and affirm the beloved when we are “in love” with him or her.

At this point, it should be apparent that sexual attraction is quite distinct from eros, just as eros can exist between persons in the absence of sexual attraction. Think of the great mystic saints, like Theresa of Ávila, who express their prayer experiences as rapturous, ecstatic, erotic. Eros and sexual attraction are certainly distinct. Yet there is a reason that they are often considered together.

If eros is the desire, permeating all facets of our being, for union with another person, and if both body and soul are constitutive of, not accidental to, human persons, then the way that we seek this union will be both spiritual and bodily. Beauty—and not just physical beauty—kindles eros in us, and since beauty for us is perceived sensually, our response in turn will include a sensual or bodily response. Our bodies, which on the one hand demarcate our separateness, are the vehicles through which we strive to realize our desire for union. Lewis frames this erotic phenomenon with his typical grace: “The longing for a union which only the flesh can mediate while the flesh, our mutually excluding bodies, renders it forever unattainable can have the grandeur of a metaphysical pursuit.”

Our erotic desires transcend our bodies’ ability to satisfy them. Especially in erotic love, we want to become one with the beloved, but we mustn’t think of this oneness only in physical terms—or only in non-physical terms, for that matter. The fullness of eros is the intercommunion of whole persons, two separate “I”s coming together as one while remaining distinct. This union is reflected and truly embodied in the act of intercourse, which is sacramental in this sense, but no amount of sexual satisfaction can exhaust our erotic desires; they cannot be exhausted at all. Lewis wrote that, “What happens in erotic love is thus not ‘gratification’ but an opening of the sphere of existence to an infinite quenching that cannot be had at all ‘here.’”