Aged Zen Buddhist Jew composes Christmas smash: who said pop music was lost to irony? Venerable bohemian Canadian poet-monk gets his first (and no doubt last) number one, moreover, thanks to a TV talent show and a young performer who plainly has not a single clue what she is singing. Just as well, really. Leonard Cohen, were he to bother to comment, would no doubt judge all this to be droll.

He might then add one of those long words the poets use. Serendipity, perhaps. How else should a 74-year-old react when he has been forced back to work because his business manager has made off (allegedly) with his pension money? Should he explain that just because he called a song "Hallelujah" he was not, in fact, contemplating a Christmas choon? Or should he remind himself that upwards of a quarter of a million in unexpected royalties never goes amiss?

A less festive work than Cohen's song is, nevertheless, hard to imagine. Depending on the version you choose, the best it gets for God is "maybe". In fact, whoever pre-selected Hallelujah for the eventual X-Factor winner (Alexandra Burke, as it turned out) is either not fussed about lyrics and stuff, or a subversive Old Testament scholar with a weakness for dark sexual metaphors. I'm guessing the former.

For Cohen and his devotees, meanwhile, the ironies just get better. There may be a daft internet campaign going on to gain chart "justice" for Jeff Buckley's fine 1994 reading of Hallelujah, but the emergence, even survival, of this re-discovered "classic" was lucky indeed. Or possibly miraculous.

When he recorded the song Cohen retained a following in Europe, but had lost any such audiences in America. The 1984 album Various Positions (doesn't that just say "Christmas"?) containing Hallelujah failed even to gain a release in the United States. Back then, it could have been the singer's last, languid hurrah. Instead, it is revived - or do I mean resurrected? - hilariously, a quarter of a century later, thanks to X Factor. And all for Christmas. Heartwarming.

That's not a word you could apply to the song itself. Or rather, the songs themselves. The number of verses Cohen spent a year writing has never been established exactly. In his own accounts there are, in effect, two separate sets of lyrics. John Cale, when he requested the words, was faxed umpteen verses, each as lugubrious as the last. And all, in their imagery - Samson and Delilah, the Song of Solomon, the story of David - entirely pre-Christian. Less Top Of The Pops than Top of the Torah. Happy Hanukkah.

We inveterate pop snobs, the ones who always said Cohen was witty, not depressing, have known all about Hallelujah since the writer was a spry 50-year-old. Hearing it - what's the polite word? - reimagined as an inspirational power pop ballad is disconcerting. Still, bizarre as Cohen's lurch into the limelight seems, there is a vindication here for all those once dismissed as "singer-songwriters". Like Cohen in old age, they labour on in the Tower of Song. As hindsight arrives, they emerge, in fact, as a remarkable generation.

Some still believe that Buckley wrote Hallelujah. Others even think Jon Bon Jovi - "You don't really care for music, do ya?" - wrote it. Dylan's version is OK (covers are not his strong suit). Rufus Wainwright, generally fearless, sounds cowed. Among the dozens of others who have mistaken a chorus for a message there is little that is memorable. But if Cohen's various renderings intimidate, try Cale. A Welshman, a piano, live in 1992: Fragments Of A Rainy Season, if you can find it. Glad that's sorted out.

As yet unresolved, however, is the strange meeting between Cohen and the X Factor audience. Will they now all rush out to buy Death Of A Ladies' Man? Will Richard and Judy find a place in their hearts for the novels and the intense books of verse? Will we all have a Zen Christmas? And will rhetorical questions come back into fashion?

You could joke about Ms Burke's brave, enforced sojourn in what is clearly, for her, uncharted chart territory. She would rather be duetting with Beyonce than tangling with weird ancient poets and who, on balance, could blame her? This doesn't alter the fact that the surreal list of Britain's Christmas number ones has a piece of actual art on its roster. If nothing else, a 24-year-old song stands as proof that a formerly fly-by-night genre has proved itself remarkably durable.

Cohen is old. This is not disputed. Yet the septuagenarian's performances during his pension-redemption tours stand high on those lists of "gigs of the year". By all accounts, a good number of the Glastonbury crowd had only a sketchy knowledge of the svelte gentleman in the fedora, and yet he was a sensation. Tom Waits and Randy Newman, younger but no longer mistaken for spring chickens, also returned to Britain to demonstrate that, if anything, their music has become more testing, more daring, as they have aged.

The greatest of them all, Bob Dylan (born in 1941), will be back next year amid what is, even by his standards, a renaissance. Whether what he does with that voice of old, crackling leather still has anything to do with pop music is open to question. But that's not the point: pop - or the American popular song - is where it began, and the means by which it continues.

Longevity was supposed once to be the preserve of jazzers and bluesmen, of a Sinatra, a Johnny Cash, or a Tony Bennett. Now the 1960s survivors, those who expected nothing more than a couple of years of pay cheques, draw on bodies of work almost half a century old. Dylan, Cohen, Neil Young, Van Morrison, Waits, Cale, Joni Mitchell, Lou Reed, Newman, even young Springsteen: not for every taste, perhaps, but representative of something larger, now, than those absurd Rock and Roll Hall of Fame inductions. Pop, as you must call it, was once written off as the cadet wing of popular music. It was never meant to last. But it lasts.

Which is nice, no doubt, for the middle-aged among us. Yet this is not, I hope, one of those music-isn't-what-it-was lectures. There is plenty of new, good song-writing around. The Fleet Foxes album was, for an example, one of the best things I happened to buy this year. I could give you chapter and verse on its "references" and influences, but I could do that with half of Dylan's catalogue, too.

That's how the craft of song writing proceeds. And it is not entirely fanciful, for my money, to compare Cohen with Cole Porter in terms of wit, subtlety, or respect for the language, or to say that the Bob surpassed his hero, Woody Guthrie, decades ago, and that a nomination for the Nobel literature prize was the opposite of ridiculous. These old music-makers pass the test: they remake themselves continually. If nothing else, Cohen's "comeback" with I'm Your Man should never have surprised as many people as it did.

Still, he wouldn't last five minutes on X Factor. Can't sing, you see, even if he will persist in claiming that he was "born with the gift of a golden voice". Like writing a Christmas number one, that's his little joke. And who knows: perhaps a few of the thousands downloading Ms Burke's recording this weekend will pause over the lyrics and wonder what the old guy really means by a cold and "broken hallelujah".

Cohen will accept his windfall serenely, no doubt, in a Zen sort of way. The very fact that a song that has nothing to do with Christmas is being mistaken for a Christmas song amid mass hysteria over a contest that has nothing to do with the craft of song writing probably counts as an art event in itself.

But hold on: here's the chief rabbi delivering his Thought for the Day on the radio. He says that Hallelujah is all about faith. I'll believe it if you will, rabbi. Then I'll believe that X Factor is believable.

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