Monogamy, non-monogamy and the rules of a union

…the best thing is to explain each case separately, without trying to generalise.

— Anton Chekhov, “About Love” (1898)

Two couples call themselves monogamous. In the first, people count only sexual contact as cheating and are relaxed about flirting, texting and close friendships with exes. In the second, dinner with someone you are attracted to already breaks the rule, even if nobody touched anybody. The sign on the door says one word; inside, different agreements are in force. Relationships are not built in only one way, yet we often take exactly one design to be the only normal one and treat everything else as doomed or suspect. What we need is to work out which designs exist and under what conditions they hold. The sign decides less than the mechanisms common to all unions.

Two extremes hold up equally badly under scrutiny. The first declares monogamy the only healthy form and everything else a pathology. The second treats non-monogamy as the more advanced design and monogamy as a relic. Neither the name of a form nor its cultural prestige tells you anything by itself about the quality of a particular union.

Form does not produce quality

The data give a calmer picture than the argument around them. The first meta-analysis in this area, published online in 2025, pooled 35 studies and data from 24,489 participants. The mean differences between monogamous and consensually non-monogamous relationships were close to zero and statistically indistinguishable from it, both for relationship satisfaction and for sexual satisfaction. Most of the source studies were observational and relied on self-reports and self-selected samples; participants had already chosen their form of union, and cultural stigma was distributed unevenly. So the result refutes the automatic superiority of one sign over another, but it does not prove that the forms are causally equivalent, and it does not choose the agreement for particular people.

The information regime matters more than the label

One series of self-report studies found that people in consensually non-monogamous relationships reported using barrier protection and testing more often than people who concealed contacts outside a monogamous agreement. The design does not show that honesty alone produced the difference: the groups could differ in knowledge, practices and self-selection. But it does refute the automatic equation of an open form with greater exposure.

What turns out to be decisive is the union’s information regime. The available data support a narrower conclusion: the form of a union by itself explains little of average satisfaction in the self-report samples we have. To judge a particular union you have to look separately at consent, transparency, conversation, and how well the rules match what the participants want. The meaningful line runs between a consensual design and a deceptive one. Secret cheating breaks consent and trust; the number of partners by itself does not describe the harm done. The word “honest” in the phrase “honest non-monogamy” does all the work; “non-monogamy” only names a form.

Relationship designs have varied across the map and across history: monogamy; polygyny, one man with several wives; polyandry, one woman with several husbands. Monogamy compulsory for everyone is a comparatively recent norm. “The only correct form” usually turns out to be a local custom rather than a law of nature: biology supplies a mix of dispositions, not a ready-made prescription.

Naming the form is not enough for a working agreement. The participants have to settle separately the limits of sexual and emotional exclusivity, whether new contacts must be disclosed, the rules of safer sex, the sharing of time and common resources, the procedure for changing the terms, and the right to stop the experiment. It is on these points that one and the same label turns into different unions.

Cheating is not one more form of relationship

Here it helps to draw a line that everyday language keeps blurring. Consensual non-monogamy changes the rules before the act: the participants know what exactly is permitted, what has to be reported, which risks are accepted and where the right to stop the experiment remains. Cheating changes the rules unilaterally and hides the fact of the change from the person who will carry part of the consequences. These are different information regimes, not two versions of one design with different levels of nerve. In one, people make decisions knowing the terms; in the other, one participant goes on making decisions about sex, health, money, time and the future on the basis of a forged picture of the union.

A secret breach usually has several layers of damage, and the sexual act is only the most visible one. The first layer concerns exclusivity itself: the partner did what the agreement forbade. The second concerns information: the other person was denied the chance to choose whether to continue the relationship on new terms. The third concerns the external effects the breaching partner transfers to them without consent: the risk of infection or pregnancy, the spending of shared money, the reallocation of time, the emotional labour of maintaining the secret. The argument “it was only sex” often misses the point. For one person the event may have been a short episode; for the other it retroactively changes the meaning of many decisions made in ignorance.

Confessing after the fact matters, but it cannot manufacture consent retroactively. It can end the information asymmetry and open the possibility of repair, but it does not turn a past breach into consensual non-monogamy. What follows is the work of repair: acknowledging the damage, changing behaviour, restoring verifiability, and the other person’s right to decide whether they want a new agreement at all. Demanding that everything be “put in the past” immediately usually means asking for trust back before there is any data for a new forecast.

The difficulty is that many couples never spelled out the rules in detail. They know the word “monogamy” but never agreed whether the ban covers a kiss, sexting, a hidden emotional attachment, former partners, paid sex or an account on a dating app. Not every ambiguity is a deliberate loophole, but pointing to the absence of a detailed written annex does not settle the question either. The high cost of a mistake and the importance of the rule make an imagined overlap of meanings unreliable. The agreement is needed because one word often hides two different contracts. So it is better to agree on the meaning of the rule in advance than to argue afterwards about whether the breach was “obvious”.

This line works in the other direction too. A formally monogamous union does not become honest merely because outside contacts are absent: exclusivity obtained through threat, financial dependence or the impossibility of refusing safely remains a bad agreement. And conversely, an open form does not release anyone from obligations; there too you can lie, hide risk and break agreed limits. The main axis does not run along the number of partners. It runs between changing the rules together and quietly appropriating the right to change them alone.

The participants choose the form of their union, but the name is not what makes it durable. Consent, transparency, workable rules and a procedure for revising them do. Monogamy works when its boundaries are understood the same way by both and the choice is free; an open form does not cure silence and does not release anyone from obligations. So agreements should be taken apart point by point: what is permitted, what gets reported, which risks are accepted and who has the right to change the rules. Only after that does the word on the sign start to describe an actual union.

Main sources

Conley, T. D., Matsick, J. L., Moors, A. C., & Ziegler, A. (2017). Investigation of consensually nonmonogamous relationships: Theories, methods, and new directions. Perspectives on Psychological Science, 12(2), 205–232. Comparable results for satisfaction, commitment, jealousy and trust. On the “halo of monogamy” and the doubtfulness of its automatic superiority: Conley, T. D., et al. (2013), Personality and Social Psychology Review, 17(2), 124–141.

Rubel, A. N., & Bogaert, A. F. (2015). Consensual nonmonogamy: Psychological well-being and relationship quality correlates. Journal of Sex Research, 52(9), 961–982. Similar well-being and relationship quality; monogamy does not turn out to be necessarily “healthier”. On the link between openly negotiated non-monogamy and safer sex compared with secret cheating see: Conley, T. D., et al. (2012), Journal of Sexual Medicine, 9(6), 1559–1565.

Anderson, J. R., Hinton, J. D. X., Bondarchuk-McLaughlin, A., Rosa, S., Tan, K. J., & Moor, L. (2026). Countering the monogamy-superiority myth: A meta-analysis of the differences in relationship satisfaction and sexual satisfaction as a function of relationship orientation. Journal of Sex Research, 63(1), 130–142. https://doi.org/10.1080/00224499.2025.2462988. The meta-analysis covered 35 studies (N = 24,489); the authors note separately the limitations of self-reports, sample composition and the heterogeneity of non-monogamous forms.

Institutions set the frame, but they do not allocate every evening, every purchase, every touch and every refusal. Shared life is produced in small repeated decisions: who reschedules plans, who remembers deadlines, who finds it easier to say no, how the couple handles unequal desire, recurring conflict and damage already done. This is where the big words — love, care, compromise, forgiveness — most often conceal the machinery of everyday power.

In the economic model a household consists of several centres of will. Inside it there are at least two welfare functions, different stocks of time, money and health, and different outside options. A couple is able to create a joint surplus, but the fact that it exists says nothing about how it is divided. Everyday life meanwhile remains a repeated game and an incomplete contract. Repetition allows care to be answered with care, reputations to be built and accidental mistakes to be repaired — or bad treatment to be carried over to tomorrow, if the other person will stay anyway. It is impossible to write down in advance every night with a child, every change in desire and every illness; the gaps are filled by habit, power and de facto control.

Finally, many family outcomes are produced jointly. A clean flat, a calm child, sexual closeness, the feeling of home and a relationship kept alive cannot be attributed entirely to one participant. These are common or club goods: both use them, but the contribution can be shifted onto the other. Hence the free-rider problem, moral hazard and arguments about a fair share — even if nobody says those words in the kitchen.