The best summary (and most unemotional argument I’ve ever seen posted on the internet) of the different definitions of marriage debated within the US today is made in the paper “What Is Marriage” published in the Winter 2011 Harvard Journal of Law & Public Policy.  I highly recommend reading the entire paper, but this post from the blog Theo-sophical Ruminations gives a summary:  http://theosophical.wordpress.com/2011/06/15/the-best-argument-i%E2%80%99ve-read-for-traditional-marriage-and-against-same-sex-marriage/

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I’ve often said the reason support for same-sex marriage has grown so fast in the West is because we have ceased to understand what marriage is. George et al understand that when it comes to the marriage debate, everything hinges on the question, What is marriage? Does marriage have a nature independent of cultural norms, or is it a mere social construction that can be whatever society wishes it to be? The authors rightly begin their paper by defining and contrasting these two perspectives (what they call the “conjugal view” and “revisionist view”):

Conjugal View: Marriage is the union of a man and a woman who make a permanent and exclusive commitment to each other of the type that is naturally (inherently) fulfilled by bearing and rearing children together. The spouses seal (consummate) and renew their union by conjugal acts—acts that constitute the behavioral part of the process of reproduction, thus uniting them as a reproductive unit. Marriage is valuable in itself, but its inherent orientation to the bearing and rearing of children contributes to its distinctive structure, including norms of monogamy and fidelity. This link to the welfare of children also helps explain why marriage is important to the common good and why the state should recognize and regulate it.

Revisionist View: Marriage is the union of two people (whether of the same sex or of opposite sexes) who commit to romantically loving and caring for each other and to sharing the burdens and benefits of domestic life. It is essentially a union of hearts and minds, enhanced by whatever forms of sexual intimacy both partners find agreeable. The state should recognize and regulate marriage because it has an interest in stable romantic partnerships and in the concrete needs of spouses and any children they may choose to rear.

They go on to argue that only a conjugal view of marriage is able to offer a principled basis for marital norms, results in the common good of society, and that a departure from this norm in favor of the revisionist view will damage the long-term health of society.

What Makes a Marriage a “Marriage”?

What is marriage? Most will agree that marriage involves three elements: (1) a comprehensive union; (2) a unique link to children; (3) norms of permanence and exclusivity. While most revisionists wish to dispense with the second element, few would dispute the remaining two.

Comprehensive Union

Regarding (1), while there are many important and/or intimate human relationships (filial, familial, business, etc.), a marital relationship is unique among human relationships because it is comprehensive in scope, involving every aspect of a couple’s being. A marital relationship not only involves the sharing of one’s life, emotions, will, and resources with another individual, but also a sharing of one’s body (sexual relationship, which George et al call an “organic bodily union”). A relationship that lacks organic bodily union is not comprehensive, and thus not of the marital sort.

That organic bodily union is integral to a marital relationship is evident. Imagine if two people committed to marriage on the basis of their shared love for tennis rather than on a sexually exclusive relationship. Would that make it a marriage? No. It would be indistinguishable from a friendship between roommates. Sexual intercourse is necessary for a bodily union – and hence marriage – because our reproductive organs are the only organs we possess that naturally require the aid of another human being to fulfill their intended purpose. All other bodily systems such as digestion and circulation can fulfill their natural function on their own. Only in sexual intercourse are two bodies “coordinated for some biological purpose of the whole,” and thus sexual intercourse is required for a bodily, organic union of persons:

It follows that for two individuals to unite organically, and thus bodily, their bodies must be coordinated for some biological purpose of the whole. That sort of union is impossible in relation to functions such as digestion and circulation, for which the human individual is by nature sufficient. But individual adults are naturally incomplete with respect to one biological function: sexual reproduction. In coitus, but not in other forms of sexual contact, a man and a woman’s bodies coordinate by way of their sexual organs for the common biological purpose of reproduction. They perform the first step of the complex reproductive process. Thus, their bodies become, in a strong sense, one—they are biologically united, and do not merely rub together—in coitus (and only in coitus), similarly to the way in which one’s heart, lungs, and other organs form a unity: by coordinating for the biological good of the whole. In this case, the whole is made up of the man and woman as a couple, and the biological good of that whole is their reproduction.

Two people of the same sex cannot achieve organic bodily union because they do not share any bodily functions that require a coordination of their bodies. If they cannot achieve organic bodily union, and yet organic bodily union is required of a comprehensive union which, in turn, is an essential element of a marital relationship, then it follows that the same-sex relationships are not, and can never be a marital relationship.

A revisionist could deny that organic bodily union is required for a relationship to be of the marital sort. If so, then why not provide two same-sex roommates with marriage benefits if they desire to get married? What about best friends? Wouldn’t it be discriminatory to prevent them from exercising their right to marriage on the grounds that their relationship is neither romantic nor sexual? If so, then the fact that two people of the same sex are having a sexual relationship should not privilege their relationship above anyone else’s.

We might even ask why three romantically involved individuals cannot marry. Why should they be prohibited from exercising their marital rights just because there are three individuals who are romantically and sexually involved rather than two? On the revisionist definition of marriage there is no principled reason to forbid this, but on the conjugal view there is: two—and only two—people of the opposite sex can create an organic, bodily union. Furthermore, children can only have two biological parents, which makes sense of why marriage has always been understood to be between two individuals of the opposite sex (no more persons are needed to create a child).

Unique Link to Children

Regarding (2), a marital relationship is naturally oriented toward children. This naturally follows from the organic bodily union between spouses since children are the telos of the human reproductive system. There is a connection between children and the way marriages are created and renewed: sexual union.

What about same-sex couples who are raising children together? Does this justify opening up the institution of marriage to same-sex couples? No. A commitment to raise children together, by itself, does not make a relationship of the marital kind. Two brothers who commit to raising their deceased sister’s child together do not thereby acquire a marital relationship. Furthermore, our social and legal traditions have always recognized a couple as married prior to the birth of their first child. A childless couple is still married in virtue of their comprehensive union and mutual commitment to permanence and exclusivity. The kind of relationship and union they enjoy is naturally oriented toward procreation, and thus is a genuine marriage even if they cannot, or choose not to have children. This is analogous to a sports team. The structure of the team is such that it is naturally oriented toward winning. If may fail to win any games. While it would fail to reach its telos, it does not cease to be a team.

Permanence and Exclusivity

Regarding (3), the conjugal view of marriage makes sense of our intuition that the marriage ideal entails permanence and sexual fidelity. Organic bodily union makes sense of the permanence of marriage since it involves a coordination of our reproductive system into a single whole. Just as we remain joined to the rest of our bodily systems for the duration of our life, we are to remain with our marital partner (our other sexual half) for the duration of our life as well. Relationships that lack such bodily union have no rational basis for such permanence.

Indeed, apart from children, there would be no reason for governments to involve themselves with the regulation of marriage:

A thought experiment might crystallize our central argument. Almost every culture in every time and place has had some institution that resembles what we know as marriage. But imagine that human beings reproduced asexually and that human offspring were self-sufficient. In that case, would any culture have developed an institution anything like what we know as marriage? It seems clear that the answer is no. And our view explains why not. If human beings reproduced asexually, then organic bodily union—and thus comprehensive interpersonal union—would be impossible, no kind of union would have any special relationship to bearing and rearing children, and the norms that these two realities require would be at best optional features of any relationship. Thus, the essential features of marriage would be missing; there would be no human need that only marriage could fill.[1]

Objections

Here’s how the authors answer key objections to the conjugal view of marriage:

How will same-sex marriage affect you?

What’s the harm in giving legal recognition to same-sex relationships? The same question could be asked of the same-sex marriage advocate regarding polygamous marriage, or any other alternative form of marriage.

One way it would affect us is that enshrining the revisionist idea of marriage into law would send a message to society that marriage is not about children, but about adult emotional fulfillment. If emotional fulfillment is the basis of marriage, then marital instability will increase because emotional unions are easily worn down. After all, what reason is there for people to stay together when their emotional connection is severed? It would be more like a friendship that runs its course and ends.

It would also obscure opposite-sex parenting as the ideal form of parenting, having erased it entirely from our legal framework. We know kids do best when raised by their biological parents, so enshrining the revisionist view of marriage into law would have the effect of causing a greater number of children to be raised in less-than-optimal family structures, increasing social disorder in the process.

It would also affect moral and religious liberty. If we enshrine the revisionist view of marriage into law, the state would be explicitly affirming same-sex and opposite-sex relationships to be equal. How would the state view those who do not see these relationships as equal, then? They would be viewed as bigots, and may suffer legal consequences for acting on their moral and religious point of view (for example, a photographer can be sued for discrimination for refusing to photograph a gay wedding on the grounds that s/he believes homosexuality is immoral).

It is unjust for the government not to recognize same-sex relationships as marriage?

No. The government is only justified in recognizing real marriages as marriages. It would only be unjust to extend marital benefits to those who are not involved in a marital relationship. The government should not be expected to call certain kinds of relationships “marriage,” that are not marriages, simply because some people are psychologically incapable of engaging in a real marital relationship. While this psychological inability is no fault of their own, this is no more reason for the government to redefine marriage to include same-sex relationships than it is to redefine marriage to include single persons to accommodate those who have not been able to find a marital partner despite their desire and best efforts to do so.

Isn’t denying same-sex couples the right to marry similar to miscegenation laws?

No. The purpose of miscegenation laws was to promote white supremacy. The problem was not that people did not think interracial relationships could form marriages, but that they did not want such marriages to be formed even when they were possible. Unlike race, sex is a relevant factor to marriage.

It’s unjust to prohibit people from marrying the person they love

There is no general right to marry the person you love. There is only a right not to be prevented from participating in a genuine marital relationship when such a relationship is possible and desired.

The conjugal understanding of marriage is based solely on religious beliefs, and thus it should not be privileged in a secular society

This is false. Although the world’s major religious traditions have historically understood marriage as a union of man and woman that is, by nature, apt for procreation and childrearing, this merely demonstrates that the conjugal view of marriage is so basic to human society and flourishing that every major religion has felt the need to incorporate it into their religious traditions. It is the demands of our common human nature that have shaped (however imperfectly) all religious traditions to recognize this natural institution.[2]

While I have tried my best, my attempt to summarize the argument of this paper does not do it justice. I highly recommend you read it yourself.