How do you forgive the unforgivable?

Until a week ago, this was a season of forgiveness – the piney advent of a new year and a new chance to renew the world's hope by turning over a new, more forgiving self. Hostilities abound, of course: 34 Americans are killed by guns every day, on average, to say nothing of the casualties of wars and revolutions in Syria, Gaza, Congo and elsewhere. Still, when the holiday season hauls around, usually the timid prospect of a less vengeful world foolishly pokes its head above the horizon again.

But there has been very little talk of forgiveness since Adam Lanza killed 20 first-graders and six of their adult minders at Sandy Hook Elementary School in Newtown, Conn. Certainly no talk of forgiving Adam Lanza; nor his mother, whom he also killed, but who owned the outsized guns her son used.

The mere idea of forgiving such atrocious crimes seems unthinkable. But I will make you a wager: Eventually, not soon but before you expect it, one or more of the parents who lost their kids that awful December day will forgive the killer.

The question is why. They will forgive, not on religious precepts or out of human kindness, but because they have to – to make the life of their dead child mean something.

I suspect their reasoning will go something like this: If no one is forgiven, even for such a crime, then everyone can be blamed by everyone else, and no one will have to take responsibility for it. Then the progress we might have made, at such enormous and heartbreaking cost, toward preventing a future Adam Lanza from wreaking havoc on the world, will come to naught.

Astonishingly, people afflicted by tragedies as devastating as the Sandy Hook killings do forgive their perpetrators. Sometimes their stories climb into you and stay there.

Izzeldin Abuelaish tells that kind of story. An obstetrician and gynecologist, now based in north Toronto, he lived most of his life on the Gaza strip (where he was born and raised in the Jabalia refugee camp) while training and working as a doctor in Israel. He speaks Hebrew fluently and has Israeli and Palestinian friends on each side of that thin border.

In September, 2009, Dr. Abuelaish's wife, Nadia, discovered that she had acute leukemia. Two weeks later, she was dead, leaving him with their eight children. The youngest was 6.

It was an especially bad time in Gaza. Hamas had been re-elected, and rockets had been fired into Israel. Israel had responded with a full-throttle blockade, weekly bombings of the supply tunnels to Egypt, and troops and tanks in Gaza itself. The bombing was severe enough that Dr. Abuelaish and the children hauled their mattresses into the dining room to sleep every night. By day, they stored them away.

Dr. Abuelaish understood that most Israelis and Palestinians wanted peace. He realized (though never approved) that desperation drove some Palestinians to suicide bombs and homemade rockets. He was able to imagine (though never support) the defensive fear that made Israel's leaders respond with multiples of that force. He thought of the situation as a cycle of vengeful mental illness perpetuated on both sides.

Then, on Jan. 16, 2009, as his children were beginning to recover from the death of their mother, Israeli tanks shelled their home and killed three of the girls. One was Bessan, his beloved eldest; another was Aya. The third, Mayar, was beheaded in the explosion. Two other daughters were severely injured. Dr. Abuelaish was in the house when it happened, and was the first to find them. One thought played over and over in his head as he moved from room to room: This is the end .

A father in that position could easily vow vengeance, or disappear into permanent grief. Dr. Abuelaish did neither. Instead, he went on Israeli TV and explained what had happened. He renounced any desire for revenge. Israel's prime minister saw the program and broke down in tears.

Dr. Abuelaish has since written a book, I Shall Not Hate , and created a foundation to encourage educational exchanges between Israeli and Palestinian girls. He was nominated for the Nobel Peace Prize.

"Revenge is not going to change what happened," he tells me. "Revenge destroys. We can't treat negative with negative. I could want to get revenge against those who killed my daughters, but they'll never come back."

He had to forgive his daughters' killers, he says, because it was the only way "not to feel angry, not to feel hate – I will never fill my body with hatred that will destroy me." He says it fiercely, again and again, as if the words were a strap to hang on to.

I tell him I couldn't have forgiven it. I would have carried my grief with me forever, as if it were my only possession.

The forgiveness industry doesn't need a special time of year any more. Two decades after truth and reconciliation commissions in South Africa proved that victims of apartheid and genocide might forgive their perpetrators, the movement is a juggernaut – everything from a school of therapy to a way to sell things.

Books, documentaries and websites about forgiveness proliferate. The Forgiveness Project, founded by journalist Marina Cantacuzino, has inspired similar ventures around the world. Her site posts first-person stories like that of Sokreaksa Himm, who in 1977, aged 14, watched Khmer Rouge soldiers kill 13 members of his family. By the age of 49, he had forgiven his tormentors. It took 35 years, but he did it.

"I began a new mission," he writes, "one that still included finding the men responsible for the deaths of my loved ones but for a new purpose. I no longer wanted to seek their deaths, but to tell them of the life and hope that I found."

Still, a few questions nag at the skeptical mind: What, exactly, qualifies as forgiveness? How is it possible? Is it necessary? Desirable? As therapeutic as revenge? Is it the same as turning the other cheek?

You would think we might have figured these things out by now. We certainly need to.

Some affronts are easier to forgive, because they are explicable. Last spring, in a courtroom in Brampton, Ont., a judge was reduced to tears when Edward Tamminga publicly forgave the killer of his 23-year-old daughter Lindsay.

She had been jaywalking when she was struck by the car of a 60-year-old father of four named Jose Cobaria. Mr. Cobaria left the scene of the accident, and did not turn himself in for two days.

"As Christians, we want to tell the court that we forgive him," Mr. Tamminga told the court.

A remorseful Mr. Cobaria apologized publicly, and the judge gave him 90 days, to be served on weekends.

Mr. Tamminga credits his Christian faith. "We grew up with the Golden Rule," he tells me. "Forgive others as you would have them forgive you."

"It's not always your first reaction, that's for sure," he adds. His voice never wavers. He was furious when he first learned of the accident, but as the facts surfaced, he felt he had no choice but to pardon Mr. Cobaria. The knowledge that he has killed someone, even inadvertently, will be "a life sentence, and we knew that," Mr. Tamminga says.

"I don't know if I would say forgiving him made the loss any less of a burden," he continues. "But what it did was assure us that we did the right thing. We still miss her, but we don't sit and stew on this guy who took our daughter away."

He adds: "I think forgiveness speaks to that mysterious part of people, that separates us from our pets – that we have the ability to do something like forgive, as much as we have the ability to perpetuate atrocities. They're at equal ends of the spectrum, but they're both incredible."

Mr. Tamminga believes that Lindsay is in heaven, "in a better place" and a very specific one, without the baggage and pain of the living.

Who would not choose to believe that if they could? But even with faith, forgiveness is sometimes impossible.

When Julie Nicholson's daughter Jenny was killed on a bus in the London terrorist bombings of 2005, Ms. Nicholson – a vicar in the Church of England – renounced her ministership. She did not blame Muslims; she had no desire for revenge. But she could not bring herself to do what her church requires – to forgive the nameless zealot who planted the bomb.

Instead she wrote a book, A Song for Jenny , a deft description of the hole of anger, the fury of loss where her much-loved daughter used to be.

I read such stories slack-jawed, at once astonished and terrified. It's lovely idea, forgiveness. But actually forgiving someone? That's another, more complicated matter.

There have been other days like Dec. 14, 2012. One of them was Dec. 6, 1989. The date has gradually become less emotional for Laurent Haviernick, whose sister Maud and 13 other women at L'École Polytechnique in Montreal died that day at the hands of Marc Lépine, who thought feminists were ruining the world.

Mr. Haviernick was 24 and on his way home from work when he heard the dreadful news. He was himself a graduate of the Polytechnique, knew the building room by room, and could see what had happened clearly in his mind.

That Marc Lépine killed himself at the end of his rampage gives Mr. Haviernick no satisfaction. Forgiveness, however, would be a step too far.

"The answer is easy for me," he says. "It's a straight no. I don't think that such an action, that destroys families, that was planned all along, I don't think we can forgive that. I'm sorry, but that's my position. Maybe I'm a bad person."

He is not angry any more, but he is not budging. He admits that the tragedy brought his mother and surviving three sisters closer; that it made him a more responsible father. He does not even favour gun control. But he could not forgive Marc Lépine, in part because there was no Marc Lépine left to receive it.

This is the second crime of those who take lives and then take their own – their crime against the survivors.

"Maybe if Lépine had lived, maybe there would be some answers," Mr. Haviernick says. "Maybe he would have said something. Running around, shooting 14 people, and then kills himself. For what?" He pauses. "To forgive, it would be a bit politically correct. And I think there is too much political correctness."

Jean-François Larivée took another route. He had been married to Maryse Laganière for four months when Mr. Lépine shot her. "And yes, it is still fresh in my mind," he tells me.

Mr. Larivée never remarried. He still bottoms out in the weeks before the anniversary, he says; this Dec. 6, he wanted to cry at work, all day. He imagines the family of three they wanted, kids he thinks would be 22, 18 and 12 today. He thinks of her whenever he vacations in Cuba, where they honeymooned, or when he sees cats, because she loved cats – the stab of the ordinary.

He remembers the details of the day too clearly, endlessly reworking them as he tries to find the one that might have changed the outcome of that evening, when police forced him to wait outside the building even as his wife was dying inside. He cries as he recounts it, 23 years later.

"I thought about Marc Lépine many, many, many times," Mr. Larivée says. "Bizarrely, only very, very, very few times have I felt any physical violence. I don't see myself killing him with his own gun, or running him down in my car. I see myself stopping him from continuing the rampage, on the stairway."

In other words, Mr. Larivée tries to forgive himself for not saving his wife, and this saves him from rage at Lépine. "The fact that I don't have anger towards him makes me think that I did forgive him, somehow, maybe."

Because there was no one alive to confront and hold responsible, Mr. Larivée instead threw himself into the causes of gun control and violence against women. "I wake up at 3 in the morning, asking, 'What was the meaning of her life?' Was that what she was supposed to do? To die at 25? What does this thing mean?

"I cannot give a meaning to the life of someone else. I can only do those things – gun control, violence against women – to give meaning to my life that lost her. To calm down the pain in myself."

The direct result of these efforts was the federal gun registry. Today, in part as a result of the dismantling of that same gun registry by the Harper government, the Ruger Mini-14, the gun Lepine used, can be easier to purchase, which does make Mr. Larivée angry: "It's a big slap in the face of the memory of my wife."

Had he lived, Marc Lépine probably would have been found insane in a court of law, just as Adam Lanza probably would have. The random act of a psychotic person, paradoxically, we at least excuse, if not forgive: The law assumes that he or she is not responsible (which may or may not be a comfort to the relatives of victims).

Having a choice in how we behave increases our responsibility to others. At the heart of the act of forgiveness is the suggestion that we can do better.

What we most easily forgive is also revealing. The heavily massaged post-Sandy Hook debate is rapidly expanding beyond gun control to how mental illness ought to be monitored and policed. At least two senior Republican legislators in Washington have stated that it would be easier, and certainly more desirable, to organize mass control of the mentally ill than to insist on rules about stocking semi-automatic weapons. In other words, they would rather forgive the gun user than the lunatic.

Many people assume that forgiveness is a feeling, a pure instinct, a one-way grant (the original meaning of the word forgive) bestowed in a swoop by the forgiver.

But more recent thinking among contemporary scholars of forgiveness maintains that to truly forgive someone, two elements are essential: You have to have someone to blame, and they have to want to be forgiven.

Only then do you experience the mutually healthful benefits of forgiveness – a newly rinsed past, a clear conscience, a fresh start.

Without a shared recognition of what has happened, of who did what to whom and why, without some kind of repentance and forgiveness, there is no progress. Without the possibility of progress, there is no hope. Without hope, there is no point. What other solace could there be for the parents of the children who died at Adam Lanza's hand in Connecticut?

Forgiveness is actually a fairly new concept. It's hard to find ancient, pre-Christian societies that thought forgiveness was a good idea at all. The ancients were skeptical that human beings could change – they preferred moral re-education techniques such as beheading.

The Judeo-Christian tradition began to change that, as did the New Testament notion that a man named Jesus died to atone for our sins. But Christian forgiveness is still highly conditional, and often confusing.

One morning, mired in philosophy – you have not experienced stroke-like incomprehension until you have tried to read a Danish intellectual analyzing Jacques Derrida's On Forgiveness – I decided to call the Most Rev. Colin Johnson, the Anglican Archbishop of Toronto.

"All people stand in need of forgiveness," Archbishop Johnson stated, right off the bat. The idea seemed to give him a bit of a lift.

A sinner who wants to be forgiven by someone he has slighted has to do at least three things, the Archbishop said: acknowledge his misdeeds, be contrite, and promise to amend his ways. "Until he does, the sinner is controlled by the sin. Similarly, the offended party needs to learn to forgive, as much as is possible. Sometimes it never happens, and that moment or event dominates the person's life, and limits their capacity for fullness of life."

The church's rules are strict, but at least they are dependable. For many of us though, in our increasingly secular lives, without God to wield his judgment that passeth all understanding, postmodern men and women have to sort out whom and what we can forgive, and how, on our own.

Even small affronts are complicated: Your boyfriend sleeps with your best friend, you gossip treacherously about a pal behind his back, your supervisor sells you down the river to further her own career – the first reaction is rage and resentment.

"Resentment is a perfectly natural thing to feel when someone hurts you," says Charles Griswold, a philosophy professor at Boston University and one of the world's foremost authorities on forgiveness. He is the author of Forgiveness: A Philosophical Exploration , and has a new paper coming out on the ethics of revenge.

Rage and resentment can lead to more of the same, Prof. Griswold says – hence the need to break the cycle by forgiving.

"Forgiving is, first of all, forgoing revenge," he says. "And in my view forgiveness also involves giving up vengeful anger."

But we need a reason to do that, and so we look to the perpetrator.

According to Prof. Griswold, he or she has to take responsibility ("yes, I slept with Sally"); repudiate the wrongful deed ("what I said about Giorgio was just nonsense – I have no idea if he snorted coke at that office party"); and express regret ("I'm sorry I wasted three days of your life by making you work on that crappy project just so I could look good to old Squirrel Paws").

Finally, the person has to commit to learning from their mistakes, to a change of self.

None of this has anything to do with the law; as Prof. Griswold says, "interpersonal forgiveness and matters of judicial punishment are entirely different." You can forgive a thief and also want him to do time.

Here's the hard-to-believe news: If these conditions are met, Prof. Griswold insists, there is no such thing as an unforgivable person. Archbishop Johnson agrees. Adam Lanza, Marc Lépine, even Osama bin Laden, if they had lived and repented – publicly taken responsibility, repudiated their actions and committed to changing their ways – were all potentially forgivable.

Whether they would be forgiven by their victims, which is the other half of the equation, is a different story.

"I do think that there are cases when forgiveness is very, very difficult, and may take a tremendous amount of time," Prof. Griswold notes.

"The victim has to come to terms with anger, and the perp has to repent, and that can take too long" – during which one party can slip back into the revenge cycle, as the Middle East proves almost daily.

"Forgiveness is not a magic bullet," he says. "There may well be cases where forgiveness is impossible, because the offender will not take the steps to be forgiven. Then you have to take other steps to get rid of one's toxic anger. But when it is possible, I think it's right to forgive."

Why? Wouldn't it be simpler to assume, as some social conservatives do, that people cannot change, and that we should therefore take an instructive moral stand and punish those who break the rules, rather than forgive them?

If you hit me, I will hit you back – not out of revenge but because you need to know that you should not hit people.

Besides, forgiveness is notoriously unreliable. We sin, repent, and go right back to sinning.

Prof. Griswold says no, "because forgiving someone who has done everything he can to be forgiven reflects the morals we all cherish: the goodness of reconciliation, the desirability of a new start, and the goodness of love over hatred. …

"Forgiveness is sort of sold as the medicine that will solve all problems. And it won't. It's really about holding the offender responsible, and both parties being held to keep their best selves."

Pardoners are idealists. Their motto is: We can do better.

I was having a drink with an old friend. It was the end of the day, and dark and noisy in the bar, which was full of Christmas shoppers. Through the window, I could see the lights of the city spread out like a lazy harem.

I said to my friend: "Maybe it's like this: Maybe your husband has an affair; maybe you retaliate. You can't bring yourself to leave him, but you can't forgive him. Instead, you hold his affair over his head, using his transgression every time you need it, as leverage, as a way to keep him there but also at a distance. Eventually this makes you feel so lonely that you actually forgive him. And suddenly, in an instant, you can leave him."

"Yes," my friend said, "forgiveness is mostly for the forgiver. I think you have to forgive just to go on living."

But the act always feels huge, ancient, slightly sacred, as if we are struggling to find within ourselves the trace of a long-lost ritual and pattern. Forgiving someone feels impossible and yet familiar at the same time.

There's a reason for that. "We have a model for forgiveness," psychiatrist Vivian Rakoff told me not too long ago. "Alas, it's a model I am only too familiar with these days."

Dr. Rakoff's son David, a well-known writer, died this year at the age of 47. "It's grief, and mourning. How can you forgive a deity who would do such a terrible thing? Forgiveness is a slow accommodation to reality. Then you move on."

Even Julian Lennon has forgiven Mark Chapman, his famous father's killer, who is still in jail.

"What am I going to do?" he told The Times of London last year. "If I don't forgive, I can't be at peace. It's not a religious statement. It's a question of self-preservation."

These days, in its most contemporary form, forgiveness looks like this: 70-odd people listening to public confessions in the rotunda of Metro Hall, an undistinguished pile of offices. It's 7 in the evening. Everything is grey: grey walls, grey floors, grey chairs. It's like sitting in a dead lung.

This is F-You, the Toronto Forgiveness Project. This is its second meeting in two years, organized by Tara Muldoon, a public-relations specialist "from a background of sexual trauma." Most of the audience is under 40; there is a large contingent of local hip-hop artists who have taken enthusiastically to Ms. Muldoon's initiative.

Arda Ocal, a local TV sports journalist, is at the front of the room saying, "Hey, guys – how's everybody doing out there?" Next to him is a screen that flashes quotations, such as "TURN YOUR WOUND INTO WISDOM (OPRAH)."

The crowd is instructed to greet one another with what one leader explains is a Swahili greeting (it means, "I see your soul"): One person says sawubona and the other replies yabo sawubona . When Nova, the woman teaching the crowd to do this, says, "Thank you for doing that," someone in the audience says, "Thank you for teaching us that." Then Nova says, " Sawubona ."

You can make fun of this earnestness, but the crowd is eager for the encounter, full of enthusiasm. To judge from the confessions of the people speaking – rape victims, former addicts, gang members, people who were once lost to themselves – it's a public absolution, a washing away of their sins in the world – not to be guiltless or irresponsible, but to escape the self-perpetuating burden of shame and judgment.

No one knows if this works in the long term, but they are trying it anyway. In two years, the movement has attracted 2,200 participants.

Rev. Sky Starr, a grief therapist/minister/educator/life coach/consultant, offers a cogent summary of the new forgiveness and its goal of "personal freedom." Forgiveness, Ms. Starr says, "used to be a spiritual thing. But now everyone is realizing that forgiveness is a holistic thing."

Forgiveness is "a skillful means of promoting internal harmony, free from regret and inner conflict. … It's not for the person who hurt you. It's for you." Why? Because "holding a grudge is letting someone live rent-free in your head." And because "hurt people hurt you because they're feeling hurt."

"One thing I learned," a rapper named Friday says, "when you can't forgive, and can't take accountability for your actions, you're always playing the blame game." Friday was a perpetrator, not a victim, but this is what he needed: a break from feeling like a bad guy. "I'm not perfect. I think it's harder to forgive yourself than to forgive others."

Eventually I speak to Stephanie (Ivory) Conover, a woman in her 20s who was raped when she was 13. She is a singer, dancer and model, a former Miss Canada Plus. I want to know why she felt she had to forgive herself for being raped.

"For accepting the fact that there was nothing I could have done," she says. When she finally reported the assault to the police, they asked her if she had led the man on, and she never pressed charges. She had to forgive herself, she said, "because I had serious anger and trust issues that had arisen from not making peace with this catalyst that was literally thrust upon me, forgive the pun."

If the world has treated you badly and left you to blame yourself for your misfortune, and you hate yourself hard enough, you come to hate the world. Perhaps this is what happened to Adam Lanza.

But if you can forgive yourself, maybe you can love the world again. All these people are trying.

In the nearly four years since Izzeldin Abuelaish's daughters died, the Israeli Defence Forces have admitted that they fired the shells that killed them. To this day, however, the doctor is still waiting for a formal apology, and has sued the Israeli government in hope of getting one.

"I'm doing it because I want all of us to take responsibility, finally, for our acts," he says. "From goodwill, not to blame."

He forsook hatred of his daughters' killers, forsook revenge, not to let the Israel Defence Forces off the hook – as some Palestinians accuse him of doing – but, again, to break the familiar cycle of despair, provocation, retaliation and revenge. He was hoping to make it possible for the Israeli military to admit its responsibility without vengeful reprisals, and to find in stout forgiveness the root of a lasting peace – a meaning for his lost daughters' lives.

"Forgiveness is to move forward," he told me, as if it were the most self-evident truth. "Not blindly: You touch it, and you engage with it. Forgiveness is to move forward stronger, more determined, and to challenge the perpetrator, and not be the victim."

But that is a two-way street, and that is the problem. "No one has approached me to ask for forgiveness," he says. "That's the issue. … Why all the time is the focus on the victim? It's an injustice to ask the victim all the time to forgive. We need to change it, and ask the perpetrator to come forward and ask for forgiveness."

That is the hard part. Asking for forgiveness is always terrifying, not just because it might not be granted, but because of the implications of the request – that we are somehow responsible for one another, that we have a collective hand in one another's losses, that we owe each other amends, sometimes even by assuming the burden of responsibility for the random and the inexplicable.

Not that we are all to blame for the sins of the world, but that we are responsible for them. What else are the massive public outpourings and debates and conversations that follow tragedies like Newtown but an effort to come to terms with the collective loss, to admit to our collective failure?

So far, in a small, unspeakably sad town in Connecticut, only one young man is said to be guilty, and he is no longer alive to give the grieving comfort. Perhaps it lies to the rest of us to step up and ask for their forgiveness too.