
The titular question was posted in a friend's locked entry. I want to write a response and utterly failed to do so within the confines of the LJ comment. So I'm trying it here. This post is unlocked so that person, and maybe others, can respond anonymously if they choose.
Please also add in the appropriate leavening of "for me" in the paragraphs below. I'm speaking of my own beliefs and ideas, with the recognition that they're embedded within a class, gender, and culture context.
Dear Anonymous
I think you're coming at this from the wrong angle. What is a marriage? A marriage is not the set of rights and obligations bundled up with the legal and religious marriage license, though those are tremendously important and extensive. Focusing on those things doesn't get at the core of what I think you want to get at.
A marriage is a commitment to the creation and maintenance of a shared entity - which I shall call "a life" - that is somehow co-extant with the people involved, be they male-female or otherwise identified. When Bill Gibson was asked to define 'cyberspace' he used the analogy of two people talking on a telephone. The people are in separate physical locations but they talk and somehow the conversation doesn't happen in either of the two places where the people are. The conversation happens in a space that is defined by the boundaries of the people and the interaction - a third space. Marriage is like that: it's a life that is created and co-exists with the lives of the people involved, but isn't either of their lives. It's something they share uniquely and that ends when they leave it.
The marriage license and ceremony are the formal conveyal of the bundle of rights and responsibilities we've put together because we (society) found marriage to be a useful and worthwhile life and we wish to promote it. There are all kinds of threads that go into that bundle, such as the state having someone to point to as responsible for children. But none of these threads IS marriage, nor is it the meaning of the marriage. Religions also try to assign meanings to marriage (e.g. "holy matrimony") and thereby invest the creation with a spiritual and often obligatory dimension. But whether or not you buy into that, the religious layer isn't the marriage.
In order to nurture and grow this new life two things have to happen. One is a shift in the mindset of the people involved. That shift is often not concurrent with the ceremony. For some people it is the "man and wife" bit or similar that causes them to feel _really_ married; for myself it's different. I have known when I was married and when I stopped being married the first time, and shared that knowing with my partner at the time. The ceremonies came later.
The second shift is a reordering of priorities. The importance of the shared life is placed above most other things. Just how far up the priority chain it goes depends on a lot of things, but the marriage gets consideration in most everything from when it's formed to when it's done. The people in the marriage commit to working on it, maintaining it, defending it from threats both internal and external. That means a whole range of different things I couldn't possibly enumerate in detail even if I tried. But I feel the details aren't as important as the attitude, priorities and treatments that the people in the marriage adjust to.
Now I want to backtrack slightly and layer on a second claim that a marriage is also a place. Pygment has a picture of herself leaning her head on my shoulder. She asked what she should call it. My response was that I would call it "home." That's the place where you're most yourself, where you're least threatened and most secure, where things are set just so and you need agreement, not permission, to repaint the walls. One of the most important defining aspects of marriage in all cultures I've seen is where the married people live. Sometimes they're expected to go out and start a new home; sometimes one of them moves into the other's household. Regardless of which way the shift happens, there's a strong correlation between marriage and home. It's a little odd to think of a person as a place, but there it is.
((I want to write more - I feel like this is both incomplete and not adequately expressive - but I've run out of cycles I can devote to this right now. Have at.))