I first read this article a few years ago and found it very interesting. Here's an excerpt: --- The essence of marriage, liberally construed Though it is often assumed that no principled liberal case exists against gay marriage, this is incorrect. In a liberal democracy, private groups may hold their own views on the desirability or reprehensibility of homosexual relations. But it is not the business of the state either to endorse or forbid such practices publicly. Neither is it the business of the liberal democratic state to define marriage in a way that speaks to the special needs of a single sect. Liberalism proceeds by taking its fundamental bearings from certain basic human experiences about which sectarians can reasonably be expected to agree--for example, the general human aversion to violent death and the claims to which that aversion naturally gives rise. Thus the first step in defining a liberal approach to marriage is to find a way of understanding marriage that is similarly true to the human situation and at the same time relatively impartial with respect to present-day sectarian conflicts. A suitable account of marriage might begin as follows: Most human societies have honored the notion that special responsibility for children lies with the biological parents. This has also been the view of almost all influential thinkers on the subject--including "liberal" ones. No known society treats the question of who may properly call a child his or her own as simply "up for grabs" or as a matter to be decided entirely politically as one might distribute land or wealth. No known government, however brutal or tyrannical, has ever denied, in fact or principle, the fundamental claim of parents to their children. Denial of this claim always demands an excuse, such as parental incapacity, criminality, or illegitimacy." (Even the infamous slaughter of the innocents, or the Pharoanic decree that landed Moses in the bulrushes, rested on fear of a future crime.) No known state or society treats the act of bearing a child--as distinguished from clearing a field or sacrificing a goat--as an entirely indifferent one for purposes of establishing a moral, legal, or familial claim. A state can override this responsibility by a variety of economic, legal, and cultural factors, but it cannot altogether cease to recognize them. This is so not only because children would likely suffer if they did, but also because most parents, among others, would not stand for it. Families are not infinitely malleable, as even champions of diversity must concede. This does not simply owe to considerations of size: A government that distributed children randomly, for example, could not be other than tyrannical. Even if it had the best interests of society in mind--say, the principle of equal opportunity, radically understood--a government that paid no regard to the claims of biological parenthood would be unacceptable to all but the most fanatical of egalitarian or communitarian zealots. Beyond its other functions--limiting female fertility, transmitting property, or providing companionship, for example-marriage is a way of honoring this central fact, which limits one's ability to regard practices of marriage as either wholly dependent on belief in a particular divine revelation or as wholly "socially constructed." But marriage is not merely a matter of biology. That children can be "illegitimate" suggests that the biological facts of parenthood are not enough for social purposes. Disputes over fatherhood, for example, or variations in parental attachment to their children, make it reasonable for societies to supplement and sometimes override the natural bonds established by and through the processes of human generation. Marriage is, before all else, the practice by which human societies mark, modify, and occasionally mask these bonds. Like death, and the funereal rites that universally accompany it in one form or another, human generation has a significance that is more than arbitrary, if less than obvious. Marriage is the primary way societies interpret that significance, and it is doubtful whether any other custom could substitute for it adequately. Whatever else it may accomplish, marriage acknowledges and secures the relation between a child and a particular set of parents. Whether monogamous or polygamous, permanent or temporary, marriage never fails to address this relation--at least potentially. It establishes a legal or quasi-legal relation of parenthood that draws on, even as it enhances and modifies, the primary human experience of generation and the claims and responsibilities to which it naturally gives rise. A husband is, until otherwise proven, the acknowledged father of his wife's offspring, with recognized rights and duties that may vary from society to society but always exist in some form. And a wife is a woman who can expect a certain specified sort of help from her husband in the raising of her offspring. All other functions of marriage borrow from or build upon this one. Even marriage among those past childrearing age or otherwise infertile draws on notions of partnership and mutual aid that have their primary roots in the experience of shared biological parenthood. An inevitable question follows from this understanding of marriage: Can those who are not even potentially partners in reproduction, and who could never under any circumstances have been so, actually "marry"? --- There's much more in the actual article. You can also download the PDF directly from this link. I'd love to get some opinions.