In the wake of news of horrible violence of the last few weeks, such as the shootings in Arizona, the bombing in Egypt, political violence in Tunisia and Sudan, and threats to the rule of law in Mexico, it is striking to recall the stakes behind the kind of nonviolence preached by Martin Luther King.

It is fairly easy to diagnose the reasons people turn to violence, at least retrospectively. The human heart is capable of goodness, but it is also capable of becoming twisted-in upon itself: greed, anger, lust, and pride throw off-kilter the usual proportion of self-love and other-love. But the key question is why there exists in human societies a "normal" proportion of self-love and other-love: why, in other words, do we care about each other in the first place? Why do we perceive violence to be wrong?

There are two basic answers. One is broadly described as a social contract, and borrows heavily from Enlightenment-era thinkers such as Rousseau, Locke, and Hobbes. More recently, philosophers like John Rawls argue for this view. In this theory, members of a society agree on basic principles in order to safeguard order and promote shared goods. The social contract answer to the question of violence is that we refrain because we discern a collective good in safeguarding civil rights. The theory is certainly influential, giving a foundation for the U.S. Constitution as well as much national and international law.

Looking over the past century, though, we can perceive the very serious flaws in the social contract model. Who is part of the contract? Its "golden age" allowed a flourishing slave trade, and women had little or no social and economic power. Moreover, the social contract model offers little room for arguing on behalf of those excluded from the contract: unborn children, immigrants, the poor, and those near the end of lifethat is, those who seem to offer no discernible use to the society, or who seem to take up already scarce resources.

A more ancient and compelling, if paradoxical, model of social "glue" exists in natural law. Natural law is the argument that human beings discern in the world a transcendent order, an order not determined by any society or group, whose laws are always going to reflect prejudices. This transcendent order entails "laws" or basic truths that human beings can perceive using their reason, in a manner parallel to the way they discern physical laws such as gravity or electromagnetism. These laws are not created by human beings, but societies can enact laws that reflect the truths of the natural law.

The paradox of natural law is that some of the most compelling arguments in its support have arisen from violent situations: I am thinking of the judgments of the Nuremburg Courts that punished Nazis; the International Criminal Court; and the arguments for Civil Rights by Martin Luther King. For the sake of brevity I'll focus on this last example.