Some tribes can be as small as a polyamorous network of people dating each other, and Ozymandias helpfully points out that healthy relationships of people who respect each other look fairly similar, no matter what rules structure they use:
But in practice, I don’t think there’s a whole lot of difference between Reasonable Sensible People Polyamory With Rules and Reasonable Sensible People Polyamory Without Rules. My husband does not have a veto over whom I date, but he does get to have opinions. Naturally, I respect my husband’s judgment about other people, so I will listen to him to see if he’s seen something I’m blinded to by new relationship energy. Naturally, my husband respects my judgment about other people, so he will listen to me about the merits of the person he’s judged distasteful. Naturally, he doesn’t want to make me unhappy, so he will swallow his dislike and be cordial if necessary. Naturally, I don’t want to make him unhappy, so I will avoid squeeing about the awesomeness of people he dislikes. And if in spite of all this we can’t resolve the conflict, we’ll figure out how to manage it while keeping the lines of communication open so we can maybe find a resolution.