Majikthise has a post in response to my post on the word 'monogamy'. There seems, however, to have been some confusion; I don't hold that legal recognition is essential to marriage, for instance, and I wasn't really thinking about length of commitment (e.g., whether it is lifelong or not) but rather the type of commitment see themselves as being in. My thought was that it really doesn't make much sense to consider single-spouse open marriage nonmonogamous, or people who are explicitly not interested in marriage monogamous.
(Looking at the post again, I see that Lindsay has clarified the issue in a comment; she's right in her reinterpretation, and puts forward a few arguments as to why she thinks we should still stick with the common usage.)
It occurs to me, looking at some of the comments, that people might often be treating 'monogamy' as an evaluative term, or at least a term with evaluative tones. This would explain both the tendency to extend it all over the place and the tendency, occasionally found, to denigrate 'monogamy' as not so spectacular (or not so possible) any way. I tend to be irritated when people apply 'monogamy' to dating relationships, for instance, because it seems to me to be a bit insulting; but it seems that most people see it the other way: it is an insult not to call exclusive dating 'monogamy'. So there's perhaps more going on than meets the eye. I still think it doesn't make any sense to use 'monogamy' in such a way that single-spouse open marriage wouldn't be monogamous.
When I was thinking about this Friday, I actually started writing down the sorts of relationships there are (proof, is suppose, that I'm an academic, or a geek, or both). Here's my list:
(both instituted or common-law)
(Yes, it does exist, and has existed!)
(Both nontiered and tiered: by tiered I mean cases where it is possible to have two different types of spouse, e.g., primary and secondary, or wife and concubine, or what have you. Polygamous marriages can, in principle, be exclusive, open, or celibate, as well.)
exclusive dating (going steady)
Alternatives to Marriage
(i.e., marriage-like in some way, but explicitly as an alternative)
ritual nonmarital mating
ritual nonmarital nonmating 'marriages'
(Although perhaps these shouldn't count, since all the ones I can think of, like self-marriage, are purely symbolic. But they are marriage-like alternatives to marriage.)
(This admits of both informal and formal possibilities. It's usually informal, but there's a movement to try to eliminate marriage from law and replace it with polyamorous obligations, which would be formal polyamory.)
Have I missed any? (I didn't, of course, count any non-relationships.)