(CNN) The day after the massacre in Las Vegas, President Donald Trump used the word "evil" three times during a brief speech at the White House.

He called the shootings an "act of pure evil," said evil cannot shatter the country's unity and urged Americans to pray for a day when "evil is banished."

Many of Trump's conservative Christian supporters praised his moral clarity. Evil is as evil does, they said, and if anything could be called evil, it is the senseless slaughter of people enjoying music on a Sunday night, unaware that a mass murderer loomed high above in a hotel suite.

A few Republicans took Trump's line of reasoning further, arguing that evil cannot be " legislated away ," or even regulated . (Perhaps unwittingly, they echoed the liberal filmmaker Michael Moore, who says that "capitalism is evil, and you cannot regulate evil.")

In any case, progressives pounced, calling the conservatives' argument a cynical cop-out , a sop to the powerful gun lobby. The government regulates all kinds of evils, from murder to child abuse and arson. Just this week, House Republicans passed a bill that would outlaw late-term abortions, a practice that some Christians describe as " evil incarnate ." (The Catholic Church calls abortion "intrinsically evil.")

But beneath the political debate lurk questions that seldom surface except in the aftermath of horrific events: What is evil? A malignant force, a moral category, or something else entirely? Where does evil come from? And what, if anything, can we do about it?

The questions seem clear enough, but as writers and thinkers of every age have found, evil eludes easy answers.

From myths to metaphysics

When Trump described the Las Vegas massacre as "pure evil," he seemed to be saying that it came out of nowhere and was beyond anything we could comprehend, said Mark Larrimore, an associate professor of religion at the New School in New York.

"We have an impulse to use the strongest words we can find," the professor said in an interview. "There's something strangely consoling about calling something 'evil.' It puts a halo around the victims, and marks the event as not just another tragedy. It exists on another register, another moral plane."

Still, as Larrimore notes in the "New Dictionary of the History of Ideas," it's often not enough to call something "evil." We want to know why evil exists and find meaning in our suffering. And for that, we have often turned to religion.

Myths were among the earliest attempts to explain evil. The stories often ran something like this: God, or the gods, created the world, and it was good. Then humans came and mucked it up by making poor choices. It's remarkable how often versions of that story appear, particularly in Western traditions, from Pandora's box to the forbidden fruit.

In the Book of Job, evil is presented as a spiritual test, with Satan gambling with God that a good man couldn't keep faith through the breaking wheel of meaningless suffering. In other biblical passages, evil is seen as a punishment for the sins of Israel, both as a nation and individuals.

Some conservative Christians still espouse that theology. Pat Robertson, for example, once warned that God would smite Orlando with earthquakes and a meteor because Disney World hosted "gay days."

At times, though, the Bible seems to blame God for the existence of evil, Larrimore notes. In Isaiah 45:7, God tells the prophet, "I make peace, and I create evil." (Later translations say God created "disaster" instead of evil, a less tricky theological formula.)

Either way, as the Western traditions moved from myths to metaphysics, the question of God's culpability in evil became more complicated.

Thomas Aquinas, the 13th-century Catholic theologian, called evil the primary objection to the existence of God. For many atheists, it still is

Morals and motivations

One way theologians and philosophers dealt with the problem of evil was to separate suffering into two camps, notes Susan Neiman, author of " Evil in Modern Thought: An Alternative History of Philosophy ."

The first camp was composed of "natural evil," disasters like hurricanes and earthquakes. Premodern people believed that suffering was part of God's plan, Neiman says. "If you were in an earthquake, you probably did something wrong."

But a massive earthquake in Lisbon, Portugal, in 1755, cracked the foundations of that idea. Thousands died, including many who didn't seem to deserve it. European theologians and philosophers began to turn to science for technical explanations of natural disasters, essentially removing God from the equation.

That still left the second category, though: moral evil, sins that seem to be our fault. Murder, rape, arson, the whole catalogue of venal and deadly deeds. In some ways, these kinds of evil are easy to recognize, if not understand.

When evil occurs, we often obsess over motivations. Consider all the books exploring why Hitler killed 6 million Jews, or all the media reports this week seeking some explanation for why Stephen Paddock murdered 58 strangers and wounded hundreds more.

But there's another kind of evil, Neiman says, that is harder to see -- and is ultimately more destructive. It's the evil committed by people who do not have evil intentions. In this, Neiman is building on the ideas of Hannah Arendt, the philosopher who coined the phrase "the banality of evil" to describe Germans who participated in the Holocaust for mundane reasons.

"Any discussion of the evil in (the massacre) in Las Vegas should consider the evil committed with malice and forethought by someone whose motives, in the end, will probably be unclear to us," she said. "But we also have to take a look at the evil committed by all the ways in which we refuse to enact sane, reasonable legislation to protect our citizens."

Neiman said she doesn't believe political leaders who refuse to consider gun restrictions, or oil executives who exploit the earth, are necessarily acting with evil intentions. But that's irrelevant, she argues. Judgment, not intention, is the "heart and soul of moral action."

As Neiman writes in "Evil in Modern Thought," "The world must hold you responsible for what you do, since it's what you do, not what you intend, that resounds in the world."

Still, the philosopher concedes that evil is a slippery concept. Even the lines between natural and moral evils have blurred. Global warming incriminates humans for the intensity of storms that blast our cities. Neuroscience raises new questions about free will and whether we are always culpable for our actions.

As an increasing number of Westerners look to science, not God, for explanations about the world, Neiman warns against abandoning moral categories like evil.

"A lot of people believe that evil is a theological term, but I don't think we need God to call something evil, and I don't think ethics are dependent on religion."

First and last

For James K.A. Smith, evil isn't a presence, it's an absence.

In thinking about evil, the Christian author and philosopher at Calvin College in Michigan draws on St. Augustine, a 4th-century bishop who wedded biblical Christianity and classical philosophy.

Augustine believed that the possibility of evil was a risk built into creation when God allowed humans to have free will. But evil can't be a "thing," Smith explained, because everything that God created is expressly good.

"If you say that evil is some substance, you have a problem on your hands, because a good God would have brought that into existence. Everything in the universe can ultimately be traced back to God."

Instead, Smith says, he considers evil a corruption of the good, a turning away from God. To put it another way, in the Garden of Eden, the forbidden fruit was not, in itself, bad. In Augustine's view, not even the devil is purely evil; we all have some degree of sinfulness shooting through our veins.

That's why, when President Trump described the Las Vegas massacre as "pure evil," Smith said his "Augustinian spidey sense began to tingle."

"To say something is 'pure evil' is bad metaphysics. It's meant to wash our hands of the event, to say that it wasn't anything that we could prevent or are responsible for."

Smith does not think of the shootings in Las Vegas only in theological terms. As a native Canadian, he is somewhat mystified by America's gun culture, particularly the lack of "guardrails" other nations have erected to prevent people with evil intentions from inflicting great carnage.

The philosopher is also wary of assigning the label "evil" only to events of massive scale, essentially basing our moral categories on body counts.

"Some father who has abused his infant child is as inexplicable to me as something like Las Vegas. Size is irrelevant to evil."

For that matter, why are we so quick to label one mass shooting "evil" while shrugging at the thousands of incremental killings that occur in inner cities each year?

Ultimately, though, Smith said he holds hope for the future, an optimism grounded in his Christian faith that the God who created the world and gave his son to save it will not let evil prevail.

"Evil didn't have the first word in this world," he said. "And I don't expect it to have the last."

Correction: This story has been updated to correct the year of the Lisbon earthquake.