Due to the rise of polyamorous relationships in the West, the Dicastery for the Doctrine of the Faith issued a doctrinal note on November 25. This tendency is regarded as an infringement upon the exclusivity of the bond between spouses, one of the fundamental characteristics of marriage. The note is entitled Una Caro: In Praise of Monogamy, referring to the married couple becoming “one flesh,” as stated in Genesis 2:24. The dicastery explains in its document the rights and obligations that arise from the spouses becoming one by virtue of the marital bond.
As Pope Francis stated during his general audience on October 23, 2024, those bound to each other by marriage are no longer two separate persons—“me” and “you”—but have become one plural person: “we.” According to canon 1134 of the Code of Canon Law, this intimate connection possesses by its very nature an inherent, perpetual, and exclusive character.
Although Scripture recounts polygamous relationships, these accounts are generally descriptive rather than prescriptive. Such “unions,” most often between one man and several women, do not serve as moral exemplars according to the Bible. The most significant passages are Matthew 19:1–9 and Mark 10:1–12, where Jesus teaches that the married couple forms one flesh, that human beings must not separate what God has joined together, and that divorce is therefore regarded by the Lord as a form of adultery. Christ clarifies that from the beginning God intended the marital bond to be indissoluble, implying the spouses’ right to reciprocal exclusivity. Jesus explicitly refers to Genesis 2:24—“Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh”—a general statement indicating a kind of blueprint given by God for all human generations after Adam and Eve. It was only because of the “hardness of heart” of the people that God permitted divorce in the old covenant (Deut 24:1–4); divorce may be seen as a deviation from God’s original plan for humanity.
Incorporating other persons into a marriage through polyamorous arrangements is an internal contradiction, since it attempts to add something to what is already complete in itself.
A connection may be perceived here with Israel’s hardening of heart, which made it necessary for the Lord to establish a new covenant through the coming of Jesus Christ (cf. Ezek 3:7; 36:26). Through this new covenant, God softens our hearts and writes his law within them (Jer 31:33; Heb 8:10), including receptivity to the law of marriage as intended before the fall. The marital bond calls spouses to conjugal love: a total, mutual, and exclusive self-giving, implying reciprocal and unreserved affection. Polygamy is therefore contrary to conjugal love, which is by nature undivided and exclusive (Catechism of the Catholic Church, 1644–1646). Only within this intimate unity do spouses complete one another, as Pope Benedict XVI wrote in Deus Caritas Est. From this, it follows that incorporating other persons into a marriage through polyamorous arrangements is an internal contradiction, since it attempts to add something to what is already complete in itself.
Furthermore, the dicastery refers to the Song of Songs, where the two lovers declare their exclusive and self-giving love for one another (Song 2:16; 6:3). Within Christian mysticism this book has often been understood as illustrating the love between Christ and his Church, a love so profound that the Church is regarded as his body (cf. 1 Cor 12:27). A striking parallel emerges with the spouses becoming one flesh within the marital covenant (Gen 2:24; Matt 19:6; Mark 10:8). St. Paul explicitly draws this connection in Ephesians 5:21–33, where he urges spouses to love one another as they love themselves and to give themselves entirely, without reservation.
Una Caro develops this association further by invoking the covenantal love between God and his people Israel in the Old Testament. Reference is made to Deuteronomy, where the Lord affirms that he alone is Israel’s God (Deut 6:4) and that an exclusive bond exists between himself and his people (Deut 7:6). Scripture even compares this union to a marriage covenant and consequently equates idolatry with adultery (Hos 2:2–20; Amos 3:2). Just as the Lord does not admit third parties into his union with Israel, marital communion likewise cannot consist of more than two persons giving themselves wholly to one another. As Israel’s religious life is not to be defiled by pagan influences, so too the marriage bed must remain immaculate (cf. Heb 13:4).
Another topic addressed by the note is the marital union as “a partnership of the whole of life,” or consortium totius vitae (Code of Canon Law, canon 1055). Although pre–Vatican II documents and the 1917 Code of Canon Law (canon 1013) articulated a clear hierarchy of the ends of marriage, with procreation at the top, Pope Pius XI’s encyclical Casti Connubii affirmed conjugal honor—consisting of mutual fidelity—as possessing equal dignity. The Second Vatican Council’s Gaudium et Spes explicitly placed alongside procreation the establishment of an intimate partnership in which spouses give themselves exclusively and entirely to one another for “the good of the whole person” of each spouse. It is evident that one cannot surrender oneself entirely to a spouse when other persons are involved in a polyamorous or polygamous relationship. Once again, the primary model of spousal love is the love of Christ for his Church, a love that is wholly self-giving and undivided.
Finally, I would like to highlight an image of the Trinity developed in St. Augustine’s De trinitate and St. Thomas Aquinas’s Summa theologiae. Both theologians understand the Trinity as a community of love, for God is love (1 John 4:8, 16): the Father as the lover, the Son as the beloved, and the Holy Spirit as the bond of mutual love uniting them. The Catechism of the Catholic Church (2205) states that the communion of marriage is a sign and image of the communion of the Trinity—the spouses as lover and beloved united by their mutual love. Consequently, the involvement of a third party in marital communion is unthinkable.
We may conclude that Holy Scripture clearly teaches that it has been God’s plan from the beginning that marital communion exists between two persons only. Polyamory and polygamy are therefore intrinsically incompatible with one of the essential elements of marriage: the mutually exclusive and total self-giving of the spouses. Since all men and women are created in God’s image and likeness (Gen 1:26–27), all are called to holiness, just as the Lord is holy (Lev 19:2; 1 Pet 1:16). Thus, marital life too must be holy, consisting of two spouses giving themselves entirely in order to bring about the full good of one another.