In the hours after the mass shooting in Aurora, Colorado, last week, one word cut through the partisan responses to the massacre, and that word was “evil.” “Such evil is senseless, beyond reason,” President Obama said. Mitt Romney spoke of the lives “shattered in a few moments—a few moments of evil.” John Boehner described the killer’s act as “evil we cannot comprehend.”

What does it mean, in the twenty-first century, to call a person like James Holmes “evil”? In centuries past, “evil” was used to describe all manner of ills, from natural disasters to the impulse to do wrong. Today it’s used mostly to emphasize the gravity of a crime, trading on the term’s aura of religious finality. The meaning of “evil” has become increasingly unsettled even as it has narrowed, yet the word has proven to be an unshakable unit in our moral lexicon. Why does “evil” persist?

In the book “Evil in Modern Thought,” from 2002, Susan Neiman traces philosophy’s struggles with evil over several hundred years. The book is structured around two events that Neiman considers the “central poles” of the modern era, both of which threw philosophers’ understanding of evil into confusion: Lisbon and Auschwitz. In 1755, at the dawn of the Enlightenment, an earthquake destroyed Lisbon, then one of the major cities of Europe. In the era before that disaster, evil was thought to come in three varieties—natural, metaphysical, or moral—and inquiry into the concept of evil was dominated by theodicy, which is the attempt to reconcile a good and omnipotent deity with evil in the world. As Neiman shows, theodicy never really recovered from the tremors. Such vast, meaningless destruction made it much more difficult to think of natural and metaphysical calamities as acts of God. Few but religious fundamentalists would continue to use the morally inflected word “evil” to describe natural disasters.

The problem of evil became a secular one, and the philosophy of evil came to focus on the moral category: the evil that men do. In the post-theodicy years that followed Lisbon, Neiman writes, attempts to understand evil fell into three main strains: Hegel tried to explain evils as necessary steps in the march of history; Nietzsche argued that evil is a problem we brought on ourselves, by inventing moral categories that don’t reflect the ways of the natural world; while a third view insisted that evil was a clear moral category of its own, defined by acts of intentional malevolence. But just like the old theodicies, these three ways of thinking, Neiman argues, were devastated by the second main event of her study: Auschwitz, a word she uses as shorthand for the collective horrors of the Second World War.

Since Auschwitz, Evil Studies is a discipline in tatters, particularly the school of thought that argues that all evil is born of malevolence. As Neiman writes, “Precisely the belief that evil actions require evil intentions allowed totalitarian regimes to convince people to override moral objections that might otherwise have functioned”—heinous acts are all too easily rationalized by loyalty to supposedly higher values, and personal feelings of guilt are all too unreliable. The rise of brain science and genetics has thrown further doubt on what intention and will even mean. Few philosophers of any school wish to confront the problem of evil directly anymore; it’s a concept too confused by old arguments that have been overtaken by events.

Despite the confusion of the philosophers, the word “evil” is still in common use. Neiman herself is understandably reluctant to offer a single, narrow definition of her own for what “evil” means today, but what she does suggest is a useful description of what effect evil has: calling something “evil,” she writes, “is a way of marking the fact that it shatters our trust in the world.” Evil is both harmful and inexplicable, but not just that; what defines an evil act is that it is permanently disorienting for all those touched by it.

However it is used, the word “evil” continues to have a “potent, frequently dangerous, emotional charge,” the philosopher Peter Dews writes, in his 2007 study “The Idea of Evil.” “It hints at dark forces, at the obscure, unfathomable depths of human motivation.” This vestigial metaphysical tinge, he admits, gives the word an antiquated feel: “It suggests a vision of the universe as the stage for a battle of supernatural powers, which human beings may ally themselves with, but which they cannot ultimately control. It threatens the modern, enlightened conception of the world as moving towards a just and peaceable future, one which can be shaped by human will and intention.” But that’s not to say that “evil” is outmoded. The appeal of “evil,” Dews argues, “is that it offers an experience of moral depth which otherwise so often seems lacking in our lives”—a solid ballast in the fog of moral relativism.

The word “evil” no longer suggests possession by a satanic or any other kind of supernatural force. Evil requires agency; one can’t be born with it. Terry Eagleton writes in “On Evil,” his rather flippant 2010 consideration of the dark side, “If some people really are born evil … they are no more responsible for this condition than being born with cystic fibrosis.” Evil is sometimes used as a synonym for sociopathy or psychopathy, but as Jon Ronson showed in his recent book “The Psychopath Test,” those terms are nearly as uncertain and subjective as “evil” is. (See the case of Anders Breivik: an initial psychiatric assessment found him insane, but that finding was reversed after complaints, including from Breivik himself, that insanity would annul his culpability.) And in one sense, sociopathy and evil are opposites. Calling someone a sociopath is a way of explaining his or her actions, if not justifying them. We might recommend hospitalization rather than imprisonment for a sociopath who committed terrible crimes. Evil doesn’t get therapy—it gets locked away as far and for as long as possible.

To call the Aurora killer evil is to insist that he was able to choose between inflicting tremendous harm or not doing so, and chose harm. But while an evil act can’t be involuntary, evil doesn’t have to be the explicit objective of the one who commits it. Think of Jerry Sandusky, the shock of whose crimes had more to with the aggressive persistence he brought to satisfying his terrible desires than with any sense that he was motivated primarily by malevolence; Jeffrey Toobin was not alone in calling him “an evil, evil man.” But if evil is not always the product of an intention to destroy, it is always the product of a failure of intent: it’s the lack of an attempt to restrain oneself from inflicting what one knows will be great harm.

The danger of a word like “evil” is that it is absolute. The “intense semantic charge” of the word “evil,” Peter Dews writes, “lends itself to exploitation” by whoever uses it. To play the “evil” card is to cut off all debate, and to say that any effort toward rehabilitation or reintegration wouldn’t be worth the risk or heartache. The mark of “evil” demands permanent banishment or death, and we call perpetrators “evil” to relieve the guilt we might feel in applying such sanctions. And yet to try to explain evil, as with brain scans or social conditions, smacks intolerably of absolving it. It suggests that evil is part of the natural order of things, a conclusion that our sense of trust in the world yearns to reject.

“Evil” has become the word we apply to perpetrators who we’re both unable and unwilling to do anything to repair, and for whom all of our mechanisms of justice seem unequal: it describes the limits of what malevolence we’re able to bear. In the end, it’s a word that says more about the helplessness of the accuser than it does the transgressor. As Dews writes, “Basic notions of offence and punishment, of transgression and forgiveness, seem to lose their grip in the face of profound, far reaching desecrations of the human.” For those kinds of crimes, “evil” is still the only word we’ve got.

Read The New Yorker’s full coverage of the Aurora shootings.

Illustration by Lara Tomlin.