Howard Jacobson: How exhilarating to be reminded that there is such a thing as an unpardonable crime

Tutu looks to my eyes like a carrion crow, feeding on the corpses of human wickedness and sorrow

An orgy of forgiveness this week. Forgiveness and its opposite for which I am not sure we have a word. Unforgiveness? Sounds disproportionately weak. Whereas implacability, remorselessness, unrelenting vengefulness and the rest, all sound disproportionately strong. Is there no answering virtue to forgiveness which does honour to the persistence of a sense of outrage - an unsleeping consciousness of wrong - but doesn't lay waste the planet?

That, in a nutshell, has been Emily Bishop's moral quandary for the last dozen episodes of Coronation Street. Does she embrace the killer of her husband, returned after half a lifetime in prison to seek her forgiveness, or does she consign him for all eternity to his unshriven hell? If the latter, where does that leave her as a Christian? If the former ... but she cannot contemplate the former.

Though it is a profanation to speak of her in the same breath as a character in a soap opera, the Reverend Julie Nicholson, mother of Jenny Nicholson, one of the victims of the 7 July bombings, has declared herself unable to celebrate communion because of the hatred she still feels for those who killed her daughter.

The Reverend Nicholson's honesty has been universally applauded, though I suspect that what we have also been applauding is the obduracy of her grief. And, commingled with her grief, the obduracy of her condemnation of the bombers' act. At last, someone - and a Christian at that - who is prepared to call a foul deed a foul deed.

In a world of mitigations it is exhilarating to be reminded that there is such a thing as an unpardonable crime. But how holy is that exhilaration? There, in another nutshell, is the question that powered Desmond Tutu's orgiastic television series last week, in which convicted Irish gunmen from all persuasions came face to face with those whose lives they'd ruined. Neat idea for a telly programme, eh? "Iniquity Swap". I didn't watch every encounter. Couldn't. Too angry half the time, too distressed the other.

And Desmond Tutu is becoming increasingly difficult to take. No doubt his role as Grand Arbiter of Misdemeanours and Their Forgiveness served South Africa well. But he seems trapped in it today and grows more ghoulish with every reprise. Like a carrion crow, he looks to my eyes - however much he ministers to reconciliation - feeding on the corpses of human wickedness and sorrow.

Saints are made of this, of course. He who would lick the leper's sores offends us in our humanity, but performs an otherworldly function which beatification both rewards and distances. What I am trying to decide is on which side of the human/other-than-human divide forgiveness belongs.

If I am anything to go by - and mine is the only human soul on whose deliberations I am able to report with authority - forgiveness is not alien, any more than the impulse to abase oneself is alien, but they share the same indecent bed. I have never yet forgiven a wrong - a real wrong, I mean, not a minor slight - without subsequently feeling ashamed of myself. Most of the time, for which I thank the gods, I am not conscious of being on the receiving end of any serious violence or injustice.

But my mind riots in imaginary casualty, not just walking into lamp posts or the path of cyclists who run red lights, but harm deliberately done to me or those I care for, acts of thuggery or terrorism against us, to the revenge of which I dedicate what's left of my life. See me passing in the street and there's a good chance that this is what I am revolving in my mind: the savage poetry of retribution.

So what am I about? Whence the pitilessness of this fictitious feud?

My own guess is that I am exercising a muscle. I don't mean - I hope I don't mean - preparing for the time when I might need it. I mean employing something which it is native to me to possess. Unforgiveness. As underused as a lateral deltoid, but no less integral to my functioning. Thus the sense of impropriety I experience when I abandon it and shake hands with a person who has done or wished me harm, a person I despise, whose actions I hold in the deepest contempt, and who, I know, feels the same about me.

In that act I make myself less than I am. For the sake of a smile or a temporary irradiation of benign feeling, for the sake of the sensation of loving or being loved, I consent to my own shrinkage. Reader, the erotics of it - and never doubt the erotic components of forgiveness: the yielding, the compliance, the betrayal of principle for feeling, the unprotected exchange of emotional fluids - are too obscene for me to describe without disgust.

And hence, yes, that exhilaration I spoke of earlier, that release of vital energies, when someone refuses to let go of their hate. In that intransigence we recognise something wild and wonderful in our natures. That abiding ferocity, subject neither to time nor vicissitude, which Aeschylus gave the Furies. "Out of your living marrow I will drain / My red libation, out of your veins I suck my food, / show us the guilty - one like this / who hides his reeking hands, / and up from the outraged dead we rise, / witness bound to avenge their blood / we rise in flames against him to the end!"

No way for civil society to run itself, of course. We know too well where avenging the blood of the outraged dead leads. Hence, as Aeschylus sees it, the necessity for laws that put an end to each party rising in flames against the other. But then the law must measure justly the offence. Men go mad if the abominations visited on them go unremarked or unpunished.

Every time a judge weighs property greater than the person, jails the robber for longer than he jails the rapist, he lights another fire in our hearts. Every time liberal opinion half condones an outrage in the act of understanding it, flirts with the suicide bomber because the suicide bomber hates what liberal opinion hates, those fires burn brighter. We can forgive only when society condemns. That much the Furies, in their final compact with the law, demand.

In the meantime, in the absence of any agency that will give us justice, frustrated by the impotence of a liberal democracy which can no longer register the egregiousness of any crime except its own, we turn in admiration to those who won't forgive, awed by their seriousness and constancy.