Judge Vaughn Walker's decision to overturn California's Proposition 8 poured gasoline on an already raging debate about whether the state should recognize permanent, monogamous gay and lesbian relationships as marriage.

Yet at the very end of 2010, the conversation about gay marriage took a very different turn. In early December, three philosophers—Sherif Girgis, Robert George, and Ryan Anderson published one of the most important efforts in recent years to defend traditional marriage from a purely philosophical standpoint. Though the paper, published in the Harvard Journal of Law and Public Policy, was obviously less visible than Judge Walker's decision, it has momentarily managed to reframe the public discourse around a single nagging question: what is marriage?

The philosophers' own answer to this question is that marriage is fundamentally not a legal or social construction, but rather is a "a comprehensive interpersonal union that is consummated and renewed by acts of organic bodily union and oriented to the bearing and rearing of children." It's a meaty definition, but they examine and defend it with a patience and care that unlike many technical philosophical works is accessible.

Yet while laboriously and patiently constructed, their case for tradition marriage fits uneasily with popular evangelical notions of ethics. There are two points of discomfort.

First, the authors are adamant—and correct—that the case is not a religious one. Neither the premises nor the logic need special revelation for their support. Yet evangelicals have been wary of natural law arguments. As heirs of the Reformation, most evangelical ethicists have argued that the brokenness of human reason makes it insufficient to successfully persuade people in public on the basis of universally accepted moral norms. In 1994, Carl Henry uttered perhaps the strongest and most authoritative evangelical denunciation of natural law in the pages of First Things:

"What moral power, then, can serve as a potent restorative and cohesive social force? Nothing other than respect for the commandment of God given at the crea-tion of the human race. It is not by reading the entrails of evolutionary nature but by recognizing anew the Divine Valuator and a recovery of the imago dei that law will regain its power."

Second, the authors' account of marriage depends upon their understanding of the physical body that is not opposed to evangelical theology, but is certainly not a mainstream view. As they put it, "The body is a real part of the person, not just his costume, vehicle, or property." Yet as adults, we are naturally incomplete "with respect to one biological function: sexual reproduction." For this reason, inasmuch as marriage is a comprehensive union, it is "oriented toward children."

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The nature of this "real bodily union" has drawn the most attention from their respondents—and evangelicals would do well to attend to it as well. Whatever our concerns about natural law in general, the philosophers' argument about marriage depends upon the fact that the body is a "real part of the person," which cuts against many evangelical understandings of the body and its relationship to the soul. The argument itself isn't new—they draw upon George's work with Patrick Lee in Body-Self Dualism in Contemporary Ethics and Politics—but the way they unpack it in relationship to marriage and sexual arrangements deserves careful consideration, especially given the reaction in the past decade against forms of "dualism" that value the soul over the body.

Yet at the same time, there may be signs that the frost on the relationship between evangelicals and the natural law tradition is melting—or at least that the discussion between the two schools of thought is heating up. For one, evangelical retrievals of a distinctively Protestant natural law tradition have gained ground in recent years.  Stephen Grabill's Rediscovering the Natural Law attempted to wrest the Reformed ethical tradition away from Karl Barth's immense shadow, as has the work of David Van Drunen.  In February 2009, Robert George's own work Making Men Moral was the subject of a commemorative conference at Union University, which featured top natural law theologians and evangelical political theorists. The formula was replicated in mid-February of this year, as evangelical political theorists gathered at Westmont College to discuss the prospects and limitations for an evangelical appraisal of natural law.

Differences between the two traditions will remain. But the willingness among evangelicals to be challenged by the precision and reason of the natural law tradition is a hopeful sign for the renewal of evangelical political thought.

But influence goes both ways, and evangelicals may have something to offer the natural law thinkers as well. Specifically, the evangelical emphasis on the brokenness of our rational faculties because of sin may serve as a reminder that truthful accounts of the goods of traditional marriage are not enough for moral or social transformation—those interested in preserving traditional marriage need beauty as well, beauty that comes in the form of lives and marriages that reflect the beauty of the cross. 

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Albert Mohler, president of the Southern Baptist Theological Seminary, was hinting at something along these lines when he remarked at the end of a recent conversation with Robert George: "I'm thankful that he's making [these arguments] better than just about anyone else is making them. And as an evangelical, we have every reason to use natural law arguments; we just don't believe that in the end they're going to be enough."

"Speaking Out" is Christianity Today's guest opinion column and (unlike an editorial) does not necessarily represent the opinion of the publication.

Related Elsewhere:

Earlier articles on marriage include:

The Good Christian Girl: A Fable | What heeding a decade and a half of dating advice can mean. (Speaking Out, July 19, 2010)
Same Sex, Different Marriage | Many of those who want marriage equality do not want fidelity. (May 5, 2010)
The Case for Early Marriage | Amid our purity pledges and attempts to make chastity hip, we forgot to teach young Christians how to tie the knot. (July 31, 2009)