Pope Leo XIV greets newlyweds at St. Peter's Square at the Vatican after his weekly general audience June 25, 2025. (CNS/Vatican Media)
Responding to recent questions raised by African bishops concerned about the practice of polygamy, the Vatican issued a sweeping defense of monogamy Tuesday, Nov. 25.
The 40-page doctrinal note "Una Caro (One Flesh): In Praise of Monogamy: Doctrinal Note on the Value of Marriage as an Exclusive Union and Mutual Belonging," was issued only in Italian by the Vatican's Dicastery for the Doctrine of the Faith. It offers a far-reaching theological, biblical and cultural reflection on the Catholic Church's teaching that marriage is a "unique and exclusive" union between one man and one woman.
The catechism teaches that marriage requires "the unity and indissolubility" of spouses. Una Caro noted that while the church has extensively developed the doctrine of indissolubility of marriage, it said the magisterium has offered "less extensive reflection" on unity.
Unity within a monogamous marriage, the document said, "can be defined as the unique and exclusive union between one woman and one man, in other words, as the mutual belonging of the two, which cannot be shared with others."
Una Caro then traces the idea of unity in marriage across Scripture, the Church Fathers, medieval and modern theology as well as more recent magisterial developments to demonstrate the unitive effect of monogamous marriage. Later sections widen the lens to culture, noting how Indian traditions and Hindu literature depict exclusive, lifelong love, and invoking poets like Pablo Neruda and Walt Whitman, to illustrate the enduring human desire for a monogamous love.
Cardinal Víctor Manuel Fernández, prefect of the Vatican's doctrine office, said at a news conference presenting the document that it was drafted in response to a desire from several African bishops who minister to communities where polygamy is common to develop a resource to motivate people toward monogamy.
That the document was drafted to praise monogamy and not condemn polygamy "gives the document a different tone than other documents," he said.
Still, at several points the document makes clear that different forms of non-monogamy are incompatible with the church's concept of unity in marriage.
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It said polygamy, adultery, or polyamory, having multiple committed relationships at the same time, "are based on the illusion that the intensity of the relationship can be found in the succession of faces," but the document emphasized that "multiplying faces in a supposed total union means fragmenting the meaning of marital love."
"Monogamy is not simply the opposite of polygamy," it stated. "It is much more, and its deepening allows a conception of marriage in all of its richness and fertility," which the document said is tied to sexuality but "is not limited to ensuring procreation."
Drawing from St. Thomas Aquinas, the document stated that monogamy "consolidates the mutual balance between man and woman," and that there is no room for any form of polyandry, when a woman has two or more husbands, or polygamy, which the document said Aquinas "defines as a form of slavery."
While the document was prompted by the acute need to expand on the church's teaching of monogamy for Africa, Fernández said that it also serves to highlight the value of monogamy in societies without polygamy per se, but where infidelity or polyamory is practiced in private.
The document stated: "We cannot ignore that in recent decades, in the context of postmodern consumerist individualism, various problems have arisen from an excessive and uncontrolled pursuit of sex, or from the simple denial of the procreative purpose of sexuality."
"A peculiarity of recent decades is the explicit denial of the unitive purpose of sexuality and of marriage itself. This is especially due to feelings of anxiety, of always being busy, of wanting more free time for oneself, of being constantly obsessed with traveling and discovering new places," it continued. "As a result, the desire for emotional exchange, for sexual relations themselves, but also for dialogue and cooperation, disappears, as these things are seen as 'stressful.' "
In its review of magisterium, the document recounts how Pope Pius XI expressed the mutual formation of spouses could be said to be "the primary cause and reason for marriage."
"This 'broadening' of the meaning of marriage, which goes beyond the narrow meaning that had prevailed until then, as an institution ordered to procreation and the proper education of offspring, paved the way for a deeper understanding of the unitive meaning of marriage and sexuality," it said.
Una Caro also cited Pope Leo XIII's defense of monogamy as a "defense of women's dignity, which cannot be denied or dishonored even for the sake of procreation."
"The unity of marriage therefore implies a free choice on the part of women, who have the right to demand exclusive reciprocity," it said.
The Second Vatican Council likewise affirmed that marital union is "all-encompassing" and therefore possible only between two individuals, warning that any "plural" union would threaten the dignity of both spouses who would be forced to "share with others what should be intimate and exclusive, thus becoming like objects in a relationship that demeans their personal dignity," the note said.
While the document had been developed months ago, Fernández said, its release was delayed to follow the publication of Pope Leo XIV's apostolic exhortation Dilexi Te, on love of the poor, elements of which were included in the note.
"A particular sign of the couple's openness to others and the fruitfulness of their charity is manifested in their concern for the poor," Una Caro stated. "Christians cannot consider the poor merely as a social problem: they are a 'family matter'. They are 'one of us.' "
