At the close of the final 2010 Templeton-Cambridge Journalism Fellowship seminar series in Cambridge this June, after writer Rob Stein’s informative discussion of “Conscience,” as everyone began packing up, one of the moderators, Sir Brian Heap, turned to me and asked (presumably because I’d once written a book entitled Explaining Hitler): “Did Hitler have a conscience, Ron?” Having spent a decade examining that very issue, which was at the heart of my book, I was able to reply, crisply and cogently: “Um, well, I’m not sure . . . I mean, it all depends.” Yes, it all depends. It all depends on how you define conscience, and how you define conscience depends on how you define evil, the cancer for which conscience is the soul’s MRI.

Evil has gotten a bad name lately. It always was a name for some sort of badness, yes; but lately the word sounds antiquated, the product of a less-sophisticated age. Evil belongs to an old, superstitious world of black and white, and we all know now that everything is gray, right? It belongs to aworld of blame in which the Enlightenment tells us that “to understand all is to forgive all””no blame, just explanation. There are some who argue it’s an unnecessary word: Having no ontological reality, no necessary use, it’s merely a semantic trap, a dead end.

After a century that saw the slaughter of more than a hundred million souls, we seem to be insisting on one more casualty: the word evil. Perhaps because by eliminating its accusatory presence and substituting genetic, organic, or psychogenic determinism, we escape the accusatory finger it points at the nature of human nature. Things go wrong with our genes, or our amygdalas, or our parenting, but these are aberrations, glitches. The thing itself, the human soul, is basically good; the hundred million dead, the product of unfortunate but explicable defects, not the nature of the beast.

But there are losses to the glossing-over process that has made the concept of conscious evil so unfashionable. If we could rescue free-will evil from the various determinisms that have been substituted for it, we could also set free will”the freely made choice to do good or evil”free again. Doing so would reestablish the possibilities of freely chosen courage and nobility, of altruism and self-sacrifice, rather than reducing them to some evolutionary biology survival stratagem. We diminish and marginalize the idea of evil because we don’t want to face the accusatory consequences that the free choice of evil”a choice contrary to conscience”entails.

Serial killers and mass murderers are frequently spoken of, in the mumbo jumbo of popularizing science, as people “without conscience.” But if they lack conscience, they lack transgressiveness; they cannot consciously violate an entity they lack. Consider Derrick Bird, a cabdriver in England’s West Cumbria, who, on a June morning in 2010, with no evident warning signs, turned into a spree killer who murdered twelve people and then shot himself. The murders took place at a time when I was in Cambridge for the Templeton-Cambridge Journalism Fellowship and so was able to observe the cultural schism over the notion of evil and free will as it played out in the intensive coverage (virtually absent in the United States) of the murders and their aftermath.

Bird”or “psycho-cabbie” as the tabloid News of the World ’s front-page headline dubbed him”became an emblematic case study of how science and religion have shaped the split in society and culture over the nature of evil. Just take that headline moniker, psycho-cabbie. On the one hand, it melodramatizes the killings. On the other hand, it serves to defuse their malevolence: The murders were performed by a “psycho,” not a “normal” person, and psychologists tell us that psychos suffer from a disease, not from evil. They have poor “impulse control,” and so it’s not something we have to fear from normal people like ourselves.

On yet another hand, on its inside pages the News of the World featured an exclusive photo of psycho-cabbie’s dreary kitchen, a shot taken from outside his kitchen window that spotlighted a bottle of HP sauce on his sad, loner’s kitchen table. The headline on that read “the devil’s kitchen.”

Tabloids believe in evil. And yet, if someone is possessed by evil spirits, does that mean he’s a victim, too? Was the headline saying that the devil was cooking up evil in that kitchen, using his special brew of satanic HP sauce on the previously nondevilish psycho-cabbie?

It’s complicated. But at least evil is still a problem to the moralists of the tabloid press. To the bien-pensant columnists of the serious press, it’s virtually a vulgarism. On the day after the psycho-cabbie’s killing spree, The Independent ran a story on the killings by an “investigative psychologist” with the headline, “A simmering anger fuelled by low self-esteem and paranoia.”

Ah, that old (and shopworn) villain, low self-esteem. The allegedly more sophisticated media, with their investigative psychologists of various stripes, think we’re on the way to giving evil a local habitation and a name in the brain. Neuroscience will clear up the problem of evil that has troubled philosophers and theologians since before St. Augustine: Pinpoint the site of evil on this or that temporal lobe or cortical matrix and predict and perhaps interdict evil behavior.

Geneticists have recently proclaimed, with all the confidence of Columbus discovering the Indies, that they have located evil in the “evil twin” copy of the “warrior gene.” Brain-scan analysts say it’s located in “an imbalance between the orbital cortex and the amygdala,” as neuroscientist James Fallon recently informed listeners to National Public Radio. The morning before psycho-cabbie started on his murderous rounds, the ever-dependable Independent credulously informed us, at breakfast, of a different finding, in a story headlined “How a deprived childhood leaves its mark on the brain.”

Written by “Social Affairs Correspondent” Sarah Cassidy, the story promoted the brain scan“based theory being peddled by a charity called The Kids Company, which, we were told, spent £1.6 million on a study to establish that “over-exposure to fright hormones damages children’s brain development and leaves them prone to violent outbursts and unable to calm themselves” when they grow up and perform evil acts.

The story was accompanied by two scary-looking brain-scan slices, in each of which a sinister-looking, crescent-shaped swath was helpfully highlighted by The Independent in blood red to demonstrate the effects of “cortical atrophy,” seen in the difference between a “healthy three-year-old” and one who “suffered severe sensory deprivation with minimal exposure to language, touch, and social interaction.” It turns out that Rousseau’s child of nature, the epitome of unsocialized innocence, untainted by “social interaction,” is likely to harbor evil”or “cortical shrinkage””rather than natural nobility within.

The red areas bore an unmistakable, if perhaps inadvertent, resemblance to Satan’s horns, growing inside the brain, but the story was another instance of the organizing of evil, the implicit determinism: Anyone with cortical shrinkage showing up on the brain scan, like anyone with the wrong orbital-to-amygdala ratio, was destined to commit evil acts”and to be absolved of them by science because they were only the product of neuronal defects.

The Kids Company study also showed “enlarged ventricles in the center of the brain.” Now we’re talking. Hasn’t evil as an “absence of being” been a theme of post-Thomistic discussions of the subject? Hole in the brain = absence of being, no? Curiously, on the page opposite the damaged-brain scans was a story about human remains found in the river Aire in West Yorkshire that turned out not to belong to two murdered prostitutes; evidently there had been speculation that a serial killer”a cortical-atrophied, poorly ratioed orbital / amygdala type”was at work emulating the famous “Yorkshire Ripper.” The juxtaposition of stories suggested an account of evil: Cerebral atrophy means murdered prostitutes. A description of evil that, in effect, exculpated the evildoer by blaming his crimes on a bad brain scan.

Indeed, brain scans are the new phrenology of forensics, with the key bumps actually inside the head, on the soft parts of the brain, rather than outside, on the knobby protrusions of the skull. To my great satisfaction, the story in The Independent ended by quoting one of my favorite skeptics of pseudoscience, Raymond Tallis, a doctor and philosopher more well known in the U.K. than here, who suggested we not get too excited: “I do not think brain scans will add anything to what we already know,” he said. “The trouble is that that leads to a general sort of claim that ‘My brain made me do it.’ This neuromitigation of blame has to be treated with suspicion.”

Neuromitigation! Exactly the word we need to describe this organizing of evil. But evil is a problem not just for science. To promoters of a new religiosity”such as Terry Eagleton, who writes so well for someone whose thinking is so muddled, strangled in his own sophistry like Laocoön by the snakes”evil really isn’t a problem, barely exists at all. Of course, Eagleton’s sophistic denial of evil’s relevance, in a book called Evil , demonstrates even more strongly what a problem it is. As Alan Wolfe noted in the New Republic , Eagleton thinks evil is “boring, supremely pointless, lifeless, philistine, kitsch-ridden, and superficial. Indeed, lacking any substance, it ‘is not something we should lose too much sleep over. People can be wicked, cruel, and indifferent. But the concept of evil, with which theologians and philosophers have wrestled for centuries, can be safely tucked away. When it comes to evil, we must be social and economic realists. ‘Most violence and injustice are the result of material forces, not of the vicious dispositions of individuals.” The neo-Marxist Christian view of evil.

There have been few takers lately for Jung’s view that evil has an ontological reality”that it has real being, something to watch out for. Although I have met two very different people whose sanity and stability I respect who have said they have encountered the presence of palpably ontological evil. One was a New York City cop, from the Dominican Republic originally, who, because of his background, was assigned to investigate allegations of Santeria killings and a subterranean ring of exorcists who were actually extortionists.

In effect, he was often called upon in his job to try to distinguish who was truly possessed by evil spirits and who was being conned into believing it or was suffering delusions of possession. I watched him perform an exorcism in his off-duty role as spiritual counselor in an old, candlelit Lower East Side church. It was chilling. And somehow convincing.

He told me something much like what I also heard from Fraser Watts, a thoughtful, mild-mannered Anglican priest in Cambridge, also a trained psychologist, who described his experience of “deliverances,” as the Anglicans call exorcisms of those possessed by evil spirits. He conceded that most of the cases he saw were likely psychogenic, but he believed that in a few instances he felt he had been in the presence of genuine evil spirits.

Of course, even evil spirits are a problem for evil, since belief in them displaces responsibility from the individual possessed to the possessor. Still, it’s more than intriguing that similar language would be used by a hard-bitten New York cop and a soft-spoken Anglican priest in Cambridge.

Evil remains a problem, not just for its victims, though they should not be forgotten in all this theorizing, but for those who try to conceptualize it. This first came to trouble me during an exchange with the late historian Hugh Trevor-Roper, who has grown in estimation as one of the most scrupulous and discerning historians of his time.

At the end of the Second World War, as a member of MI-6, Britain’s secret intelligence service, he was tasked with going into Hitler’s bunker to reconstruct the details of Hitler’s death, in part to halt rumors of the Nazi leader’s escape and survival. In the process, Trevor-Roper learned an immense amount of previously unavailable information. This included the discovery of Hitler’s “final testament,” in which, shortly before he killed himself, he commanded the German people never to cease and desist from their war to exterminate the “eternal poisoners of humanity, the Jews””a job he’d left unfinished.

From the evidence he gathered, Trevor-Roper produced perhaps the first, certainly one of the finest, early biographies of Hitler. He agreed to be interviewed by me in the Oxford-Cambridge Club, to which I had brought a tape recorder, which I nested in the shelter of what looked like a five-century-old chess set and at which he looked disapprovingly.

“A solecism,” he said tartly, indicating the recorder. I decided to brazen it out, and I’m glad I did because I might not have retained the stark reply he gave to my question, “Did Hitler know he was doing wrong when he was committing his crimes?”

“Absolutely not,” he shot back without hesitation. “He was convinced of his own rectitude.” Yes, rectitude. All that Trevor-Roper discovered confirmed him in his belief that Hitler was a true believer”a man who did not consider himself evil but a heroic doctor, a veritable Pasteur, a great benefactor to humanity purifying the human race of infection.

This is an old”but still unresolved”philosophical question: Can someone be evil if he thinks he’s doing good, no matter how deranged his thought process? It has troubled everyone from Plato to Augustine and their heirs, but it remains a genuine problem”because most people we think of as doing great evil think of themselves as doing the right thing. Indeed, who does evil while thinking he actually is doing evil? Only a few characters in literature”Shakespeare’s Richard III, notably”and those cartoon villains twirling mustaches.

This is a hard notion to assimilate. In fact, the following week at Oxford, I placed it before Alan Bullock, Trevor-Roper’s rival as an early historian of Hitler and the author of Hitler: A Study in Tyranny . He exclaimed, with North Country bluntness: “If we can’t call Hitler evil, then who can we?” One way to sort all this out is to note that it is possible for evil to inhere in ideas as well as in men. There are evil ideas that men can become true believers in”thinking they are doing good in carrying them out. It is the intellectual version of possession by evil spirits.

In any case, back to psycho-cabbie, who raises a whole host of new questions about evil and its depiction in our culture. Beginning at 5:30 on that morning in June, the man whose name was not psycho-cabbie but the oddly cheerful name of Derrick Bird, began a killing spree that racked up twelve murders, not including his own suicide, in what was almost invariably referred to as the “sleepy seaside town of Whitehaven.”

Was he feeling “simmering anger fuelled by low self-esteem” that morning? Other psychiatrists and savants lined up to weigh in. In a full-page diagnosis in a later edition of The Independent entitled “There is no one either good or bad, but circumstances make them so,” Julian Baggiani junked “self-esteem,” “paranoia,” and other such old-fashioned jargon for “situationism,” which he announced was “the dominant school of thought in psychology and philosophy now.”

Ah, situationism, which, we were told, “claims that the best predictor of how people behave is the circumstances they find themselves in, not their predispositions.” In other words, “everyone was doing it, you can’t blame me.” As the leading theorist of situationism, Philip Zimbardo, has put it, “We have underestimated the power of social situations because we overestimate the power of individual dispositions.”

It’s sad that conventional wisdom has thrown in its lot with “situationism.” One dramatic refutation of it can be found in Christopher Browning’s study Ordinary Men , which examined the choices made by the members of one of Hitler’s killing squads in the period before mass murder had been industrialized in death camps such as Auschwitz.

Browning studied letters and diaries from members of a reserve police battalion which slaughtered whole towns full of Jews and buried them in mass graves.

Browning learned that participation in the slaughter was not mandatory; troops had the choice to opt out, and some did. Despite the fearfulness of making such a choice, they refused, of their own free will, to participate in the evil. Which removed the “situationist” exculpation from those who did.

But there’s no indication, contra Julian Baggiani, that situationism has the slightest relevance to psycho-cabbie’s choices. He made them himself. Derrick Bird left the Devil’s Kitchen at approximately 5:30 a.m. Shortly thereafter he arrived at the much larger, more luxe home of his twin brother David and shotgunned him to death.

Here we enter into one perplexing question raised by psycho-cabbie’s spree”the degrees of evil. “The primal eldest curse” is on the murder of a brother, Hamlet tells us. And a twin? It more than recapitulates the First Murder. And indeed there were other Biblical elements to the psycho-cabbie’s first murder. There was a struggle over a birthright and who was favored by the father’s blessing. Apparently the younger but better-off of the twins (David) had received a £25,000 chunk of the father’s estate”and then, when the father died, he didn’t feed it back into the evidently depleted estate to be shared with his brother.

Psycho-cabbie seemed to be wrought up over this, and over the way his solicitor had been handling it, and over the concomitant problem of Derrick’s keeping £60,000 pounds of his cabbie earnings under the floorboards of the Devil’s Living Room. He believed his brother and solicitor were “stitching him up” for the Inland Revenue so the brother wouldn’t have to come up with the £25,000 pounds.

So one could see Derrick “simmering with rage and paranoia” and perhaps even the dread low self-esteem, too. But we are all simmering to some extent. And yet: Murdering his twin in cold blood and then driving over to his solicitor’s house and shotgunning him in bed, too? Are these bad choices psychogenically determined, organically inevitable? Crimes just waiting to happen if we’d had a proper brain scan to warn us? Or are they evil? Can we utterly eliminate the fact that he had a choice, that he made a choice, and that it was an evil choice? Or do we just look at his brain scan posthumously for the real trigger? And what do we make of the nine further killings that morning, and of the dozen or so attempts that left several critically wounded?

From the murdered solicitor’s office Derrick drove to his customary post in the cabbies’ rank in Whitehaven, where he shot to death one of his fellow cabbies. There was talk that he did it because of a rumor that this poor fellow had gone out with Derrick’s ex-wife. In each of those cases one could say there was a rationale, a reason”not a good one, not an excuse, not an exculpation, but a reason, however inadequate. Does the existence of a reason, however selfish and prideful, make these killings less or more evil?

Less, one could say, because they weren’t killing for killing’s sake. They were killing for ancient human grudges against twins and lawyers, perhaps. More, one could also say, because they were killings for selfish, greedy, felonious reasons. Felonious in the sense that they were about money and rivalry and ego and emotional wounds of being second twin in a father’s love.

In capital-punishment law in most American states, premeditated murder in the first degree is not enough to put one in jeopardy of the death penalty. It must be murder in the service of, or accompanied by, another felony”kidnapping, robbing a liquor store, and or the like”to put it over the top, because the murder is then done for some kind of gain beyond mere murder.

I wonder if here the law has it backward, that killing for the sake of killing is worse than killing with some further motive. At this point, after murdering three he knew, psycho-cabbie started killing complete strangers, killing for the sake of killing. He set out in his cab and started shooting just about everyone who crossed his path, shotgunning motorists, bicyclists, and pedestrians point-blank in the face and head.

In other words, virtually every time he saw anyone”a person with whom he did not have any kind of psychogenic, emotional, legal relationship”he chose evil, more and further evil, until he totaled a dozen dead victims and then shot himself. He was in a world of utter freedom offered by the fact that he could not become any more morally or legally culpable than he already was. He was free to be as evil as he wanted to be. He could have shot himself after the first three, but he chose to blast open the faces of a dozen or so more, nine of them fatally.

The reason I focus on the factor of choice in thinking about evil, rather than its ontological status, is that giving evil ontological status”positing that it is something external that may enter into or possess a previously nonevil being”makes that being less culpable.

Perhaps it could be argued that some people are culpable in “leaving the door open” for evil. Tempting evil. But what I want to emphasize is not that I know what evil is, but that abandoning the concept of evil, refusing even to see it as a problem that cannot be reduced to organic dysfunction, is to abandon free will. Because if we are not free to choose evil, we are not free to refuse it.

Ron Rosenbaum, the author of Explaining Hitler and The Shakespeare Wars, is a cultural columnist for Slate .