This is a good point. Secret plural marriages were recognized by the parties involved, perhaps a few others, and, it was understood, God. They were relationships that in theory would become public at some point, but were not, as Beastie points out, at that time ways of bringing societally 'legitimate' offspring into the world.
That said, I'd be interested, Beastie, in how you would understand these relationships, particularly those in Nauvoo, where the underground practice became well established. If they don't fit legal or sociological/anthropological definitions of marriage, how would you characterize them?
Hmmm, good question. The relationship would be closer to concubinage than marriage, and yet it doesn’t even rise to that level, since concubines were socially recognized, but just with fewer rights than a wife. Perhaps spiritual wifery, as the term was understood by other religious sects of the period, comes closest.
Spiritual wifery is a term first used in America by the Immortalists in and near the Blackstone Valley of Rhode Island and Massachusetts in the 1740s. The term describes the idea that certain people are divinely destined to meet and share their love (at differing points along the carnal-spiritual spectrum, depending on the particular religious movement involved) after a receiving a spiritual confirmation, and regardless of previous civil marital bonds
http://en.wikipedia.org/wiki/Spiritual_wifery