Three U.S. cities have started legally recognizing polyamorous relationships, prompting discussions about whether the Constitution demands broader recognition of plural marriage.
Local ordinances test constitutional boundaries
Somerville, Massachusetts, led the way in 2020, becoming the first city to pass a domestic partnership ordinance that includes relationships among more than two adults, granting them many of the same rights and privileges as married couples. Cambridge, Massachusetts, and Berkeley, California soon followed with their own measures. Somerville has since introduced an antidiscrimination ordinance that explicitly protects people in polyamorous and other non-traditional families. These local efforts have sparked debate over whether the Fourteenth Amendment’s due process and equal protection clauses extend beyond the two-person marriages recognized in Obergefell v. Hodges.
No fundamental right under current doctrine
Current legal standards do not recognize a constitutional right to plural civil marriage. The Supreme Court’s history-and-tradition framework, established in Washington v. Glucksberg and Dobbs v. Jackson Women’s Health Organization, requires a right to be deeply rooted in the nation’s history to qualify as fundamental. Plural marriage does not meet this standard.
Monogamous marriage serves legitimate state interests, including reciprocal support obligations and clear allocation of rights between spouses and the government. In Reynolds v. United States (1878), the Supreme Court upheld criminal prohibitions on polygamy, even against Free Exercise challenges.
The decision in Obergefell described marriage as a “two-person union,” expanding access without changing its core structure. Plural marriage would replace that model with simultaneous multi-spouse status.
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The difference is important because marriage law has long favored a two-person structure based on reciprocal duties. Aristotle’s Nicomachean Ethics provides an account of the nature of monogamous, dyadic marriage and the state’s interests in maintaining this institution.
For now, the legal system treats marriage as a two-person institution. Local experiments with polyamorous partnerships may eventually force a reevaluation of this boundary, or courts may continue upholding the two-person model as a principled limit.
Equal protection analysis favors the status quo
Laws limiting civil marriage to two persons survive rational-basis review, the most deferential standard in equal protection analysis. These bans do not target suspect classifications like race or sexual orientation but regulate the numerical structure of marriage itself. Any adult may marry one person, but no adult may have multiple concurrent spouses under state law.
The state need only show that the two-person limit reasonably advances a legitimate interest. Courts have identified several such interests, including the administrability of family law and protection against intra-household vulnerabilities. A dyadic structure supports mutual obligations in legal terms: each person is uniquely obligated to one spouse. This clarity affects support duties, property rules, and dissolution.
Legislatures may also conclude that multi-spouse legal status increases risks of hierarchy and coercion, particularly when one spouse holds disproportionate power. Equal protection does not require the state to treat different institutions as identical. Two-person and multi-party marriages are not similarly situated with respect to the state’s purposes in marriage law, such as establishing mutual support. United States v. Windsor and Obergefell addressed unequal access to the same two-person institution, not the creation of a new form.
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Secular justifications for the two-person model
Critics claim monogamy limits reflect religious bias, particularly against traditions that permit plural unions. A secular justification exists: marriage as a reciprocal, enforceable bond that promotes dignity through obligation.
Aristotle’s distinction between relationships based on utility, pleasure, or virtue supports this view. The state favors unions that embody stable commitments where each partner is valued for their own sake. A two-person structure aligns with these goals by limiting institutionalized domination and promoting enforceable reciprocity.
The Establishment Clause does not disqualify laws that overlap with religious teachings. Many legal norms—dignity, equality—are defended in both religious and secular terms. The constitutional issue arises only when the state uses law to coerce religious observance or favor one faith.
In Griswold v. Connecticut, the Court described marriage as a coming together for better or worse, intimate to the degree of being sacred. The two-person model remains the law’s most significant promise concerning private life—a legal bond of mutual duty and care.
