Rule

Also: relationship rule

A constraint one partner places on another's behaviour. Modern ENM writing draws a sharp line between rules (which try to control another person) and boundaries (which govern your own actions) — and tends to favour boundaries.

1 min read · Reviewed 2026-05-24

A rule, in the non-monogamy sense, is a constraint placed on a partner's behaviour: 'you may not stay overnight,' 'you must text me when a date ends,' 'no falling in love.' Rules are extremely common, especially among couples newly opening up, because they feel like a way to keep things safe. The critique in modern ENM writing is not that structure is bad but that rules try to control another person's actions and feelings — which is both ethically fraught and, in the case of feelings, impossible.

The widely-taught alternative is the boundary. A boundary governs your own behaviour and is therefore within your power: 'I won't share a bed the night you've been with someone else without us reconnecting first' is a boundary; 'you're not allowed to share a bed with anyone' is a rule. The distinction is one of the most repeated lessons in books like More Than Two, which argues that durable security comes from boundaries and trust rather than from an ever-growing rulebook.

Rules aren't categorically forbidden — many couples use a few, especially early on, and retire them as confidence grows. But rules that try to cap how much a relationship can mean, or that bind people who never agreed to them (outside partners), are where the trouble concentrates. The healthier the relationship, generally, the fewer rules it needs.

Where this term fits in the wider picture

Ethical non-monogamy is a network of overlapping practices, identities, and structures — and Rule connects to several of them. The neighbouring terms below show how this one sits alongside the rest of the vocabulary practitioners actually use; the guide at the end is the longer-form treatment of the same territory.

Closely-related vocabulary

Boundary
A statement about yourself — what you will or will not do in given circumstances — distinguished from a rule, which is a statement about what another person must do.
Agreement
An explicit, negotiated understanding between partners about how the relationship will operate — distinguished from rules in modern polyamory writing by being mutual rather than imposed.
Veto
An agreement granting one partner unilateral power to end another of their partner's outside relationships — common as a structure, widely criticised in its strong form.
One-penis policy (OPP)
A controversial agreement in which a man permits his woman partner to have other women partners but not other men. Widely critiqued as enforcing male insecurity and biphobia rather than any coherent ethic.
Hierarchy
Any structure that formally ranks relationships, typically into primary and secondary. A key distinction is descriptive hierarchy (naming how life is actually entangled) versus prescriptive hierarchy (rules that cap how much a relationship is allowed to grow).

Questions practitioners actually ask about this

Continue reading

The longer treatment of this territory is in the guide Boundaries vs rules — and why the difference matters — Why most 'rules' between partners are really boundaries about yourself — and how confusing the two reliably undermines a polycule.

New to ethical non-monogamy? Start with the glossary for vocabulary, the structures index for the named relationship configurations practitioners actually use, and the guides for longer-form treatment of the common questions.

Sources & further reading