The standard opening move when a couple starts non-monogamy is to establish rules. No falling in love. No one we know. Always tell me everything. No sleepovers. Don't ask, don't tell. The list varies but the instinct is nearly universal: if we just specify the right parameters, we can have the benefits of non-monogamy without the parts that feel dangerous.
This doesn't work as well as it sounds. That's not an argument against having any agreements, it's an argument for understanding what rules can and can't actually do.
What rules are actually doing
Rules in CNM are usually attempts to manage anxiety about specific outcomes. "No sleepovers" is an attempt to manage the anxiety about intimacy levels with other partners. "Tell me before it gets serious" is an attempt to manage the anxiety about being blindsided by depth. "No one we know" is an attempt to manage the anxiety about social exposure and comparison.
The anxiety is real. The question is whether the rule actually addresses it or just places a constraint around the trigger while leaving the underlying fear intact.
Usually the latter. A partner who can't have sleepovers but whose other relationship is clearly becoming very significant hasn't resolved the anxiety about intimacy depth, they've just moved the conversation to "are we breaking the sleepover rule" instead of "what does this relationship mean to you."
Rules that tend to work
Safer sex agreements are the category with the best track record. Who uses barriers with whom, when people get tested, what constitutes a change in sexual health status that needs to be communicated, these are practical agreements about health risk that don't try to control emotional reality. They're specific, verifiable, and address something concrete.
Disclosure agreements can work when they're genuinely about information rather than control. "Tell me when you're considering someone new" gives a partner the information they need to stay oriented in the relationship landscape. It starts to fail when it becomes "tell me about every interaction so I can evaluate it," at which point it's monitoring rather than information-sharing.
Logistical agreements about time, scheduling, and how outside relationships interact with shared domestic life tend to be functional when they're genuinely logistical. "Keep Tuesday nights for us" is a reasonable way to protect shared time. It becomes a problem when "our nights" multiplies until outside relationships have no room to exist.
Rules that tend not to work
"Don't fall in love." Nobody controls this. The rule isn't an agreement about behaviour, it's an attempt to govern an internal state. Partners who develop feelings in violation of this rule haven't done something wrong in any meaningful sense. What they've done is discovered that feelings don't follow rules.
"No one we both know." Reasonable at the edges, but this rule tends to expand as social circles overlap, and it places constraints on who a partner can connect with based on their existing relationships rather than on anything about the new person. It's usually managing the anxiety of comparison and social exposure rather than anything the rule itself addresses.
Rules applied asymmetrically. She can date women but not men; he can have sex but not emotional intimacy. Rules that are structured around the existing partner's specific anxieties rather than mutual principles tend to fail because they're designed to protect one person's comfort at another's expense. When the constraint starts chafing, there's no principle behind it to justify maintaining it.
Rules about the relationship's future. "This will always be the primary relationship." "We won't let anyone live with us." "No co-parenting with outside partners." These are attempts to contract against emotional futures that haven't happened yet and can't be predicted. They provide temporary reassurance and then either constrain real situations badly or get renegotiated under pressure, neither of which is the stability they were supposed to provide.
The experienced practitioner trajectory
People who have been doing CNM for several years, across multiple relationships, tend to describe a similar pattern: they started with more rules than they have now. Rules got added, challenged, renegotiated, dropped. The ones that survived were either genuinely functional (safer sex practices, communication norms) or got replaced by better understandings of what each person actually needed.
What tends to replace extensive rules is something harder to establish: mutual understanding of each partner's actual needs, enough trust to raise concerns when they arise rather than pre-constraining them, and enough experience with the relationship to know what the specific situations of concern actually are rather than speculating.
What works instead
The distinction the CNM community has developed between rules and agreements is useful. A rule is unilateral, established to constrain a partner's behaviour, often without their full buy-in. An agreement is mutual, both parties understand and accept what it means, both parties see value in it, both parties have input into its terms.
Agreements also have revision mechanisms. A rule tends to be fixed until violated; an agreement has a process for renegotiation when circumstances change. "We've agreed to tell each other when a new connection becomes significant, and we'll revisit this agreement in six months" is more functional than "never develop serious feelings for anyone else."
The practical question to ask about any rule: what is this actually protecting against? Is there a way to address that directly, by talking about the specific fear, by establishing something more targeted, rather than by a constraint that tries to prevent the trigger from arising?
More often than not, there is.