When we encounter the word eros—the Greek noun to which the adjective “erotic” corresponds—we probably assume that eros is essentially sexual love. Yet in making this assumption, we hit far wide of the mark established in the thought of the Greek philosophers and continued in the Christian tradition.

What, then, is eros? Is it a purely physical love, or a love that consumes both mind and body? How does eros relate to sexuality? The traditional answers to these questions may surprise us and entail a reconsideration of how we think about and classify love itself.

In reflecting on the nature of eros, it would be remiss to neglect two great scholars whose work has had significant impact on the popular understanding of eros. Josef Pieper, the great twentieth-century German disciple of Thomas Aquinas, and C.S. Lewis, whom Pieper called “the greatest lay theologian of the twentieth century,” concisely articulate the nature and place of eros within the pantheon of Christian loves in their respective works, About Love and The Four Loves .

What kind of love is eros? In About Love, Pieper states that “eros is all demanding and needing love,” and Lewis agrees, classifying eros as a characteristic “need love.” Eros, then, is apparently something very distinct from philia (friendship), storge (natural affection) or agape-caritas (self-sacrificial love), and at first look it seems obvious that eros is “lower” than these types of love. Eros is primarily a desire, and desires are appetitive, and appetites indicate the natural inclination to fulfill ourselves. But for what is eros a desire?

At this point, Pieper suggests, one must step back and consider the broader context in which we must always situate questions of the nature of love. Love, of whatever form, is ultimately fulfillment or perfection. Without love, man is not truly himself. Man needs to love and be loved in order to be whole, in order to perfect his nature as a creature. We were created for love, by Love Himself, as St. John attests in his letters. Given this conceptual framework, eros can be understood as the powerful longing, kindled by the beauty of the beloved, for the achievement of completion or wholeness in the beloved; it elicits in us a deep desire for union or communion with another in which we seek completion. Eros, therefore, openly acknowledges the need for completion in the other. This should not surprise us: if we were made for love, we are incomplete as individuals. The communion of love can only occur between persons; indeed, this reality is expressed fully in one of the central mysteries of Christian faith, the inner life of the Holy Trinity, which can fairly be called a loving communion of persons.

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.”