Megan McArdle posts a good essay on the definition of marriage:

My only request is that people try to be a leeetle more humble about their ability to imagine the subtle results of big policy changes. The argument that gay marriage will not change the institution of marriage because you can’t imagine it changing your personal reaction is pretty arrogant. It imagines, first of all, that your behavior is a guide for the behavior of everyone else in society, when in fact, as you may have noticed, all sorts of different people react to all sorts of different things in all sorts of different ways, which is why we have to have elections and stuff. And second, the unwavering belief that the only reason that marriage, always and everywhere, is a male-female institution (I exclude rare ritual behaviors), is just some sort of bizarre historical coincidence, and that you know better, needs examining. If you think you know why marriage is male-female, and why that’s either outdated because of all the ways in which reproduction has lately changed, or was a bad reason to start with, then you are in a good place to advocate reform. If you think that marriage is just that way because our ancestors were all a bunch of repressed bastards with dark Freudian complexes that made them homophobic bigots, I’m a little leery of letting you muck around with it.

Is this post going to convince anyone? I doubt it; everyone but me seems to already know all the answers, so why listen to such a hedging, doubting bore? I myself am trying to draw a very fine line between being humble about making big changes to big social institutions, and telling people (which I am not trying to do) that they can’t make those changes because other people have been wrong in the past. In the end, our judgement is all we have; everyone will have to rely on their judgement of whether gay marriage is, on net, a good or a bad idea. All I’m asking for is for people to think more deeply than a quick consultation of their imaginations to make that decision. I realise that this probably falls on the side of supporting the anti-gay-marriage forces, and I’m sorry, but I can’t help that. This humility is what I want from liberals when approaching market changes; now I’m asking it from my side too, in approaching social ones. I think the approach is consistent, if not exactly popular.

I strongly suggest you read the whole, rather lengthy, thing – as well as the numerous comments. It’s a very good lesson in intellectual discipline. That is, with one glaring exception: Megan establishes the existence of a time-honored “institution” of marriage by observing the innumerable domestic relationships throughout history which fit her predetermined definition of marriage, and discounting, out of hand, all the myriad other domestic relationships which have existed, without any deeper analysis to determine if, in certain key elements, they are all of a kind.

Hat Tip: InstaPundit