Tea and ... what? Toast? Sympathy? No, oranges. From the start Leonard Cohen was out to surprise by cunning. No wonder, then, that he had to struggle for attention in the golden age of screamers. Janis's ecstatic rasp, Hendrix's maddened guitar, Lennon's glottal roar, even Dylan's adenoidal faux-country all made sounds through which their lyrical inventions had to fight for air, and if not quite up to snuff, those words could hide behind the wall of noise. But Cohen's minimalist drone was the drowsy couch on which his poetry lay, fully exposed, with nowhere else to go.

In the 60s, his lyrics grabbed attention through teasingly incongruous unions: "Like a worm on a hook / Like a knight from some old-fashioned book". For all I know, Suzanne did feed Leonard tea and oranges, but it was the coupling of the prosaic and the exotic (oranges, as Cohen well knows, did indeed come originally "all the way from China"), the yoking together of serenity and sharpness, that makes the line jump from the chant. Suzanne is, after all, "half crazy" so when she takes "you down to her place near the river" it may not be entirely for a picnic. On the other hand, "that's why you want to be there". OK, then, peel me an orange.

More than many great singer-songwriters of his generation (Dylan excepted), Cohen makes no bones about reaching for the heavy literary hitters for inspiration. Lorca gave him the spooky, beautifully sinister Take This Waltz - although Cohen's free translation of the Spanish arguably makes a more unsettlingly powerful poem than the original - "a forest of dried pigeons" (Lorca) becomes "there's a tree where the doves go to die" (Cohen); "take this waltz with its closed mouth" (Lorca) turns to "take this waltz with the clamp on its jaw" (Cohen).

When Cohen does invoke the canon it's usually with a shrewd knowledge of how it's been used and abused through the generations. Henry Wadsworth Longfellow's Sail On, O Ship of State, the anthem on which Cohen's Democracy builds to the marching beat of a snare drum, was written in 1850 as fears for the endurance of the Union were grave. After the civil war, the poem, set to music for choral performance, accompanied routine displays of patriotic chest-beating. But the tone of Cohen's Democracy could scarcely be less rah-rah; it's more a scalding spit in the eye. "It's comin' ... from the fires of the homeless, from the ashes of the gay ... From the homicidal bitchin' / That goes down in every kitchen ... From the wells of disappointment / Where women kneel to pray." Compared to the freakshow ferocity that dominates The Future, in which Cohen turns porno-totalitarian: "Give me absolute control / Over ev'ry living soul"; "Give me crack and anal sex / Take the only tree that's left / And stuff it up the hole in your culture". Democracy is, if not exactly warm and cuddly, at least a qualified redemption: "I love the country but I can't stand the scene". The starchy Longfellow anthem gets made over, in the election year of 1992, into a disabused song of possibility.

For a while, projecting his own bouts of depressive melancholy on to the state of things, Cohen specialised in acid-burn nihilistic jeremiads, demonic impersonations of the forces of darkness, growled at the mic. The Book of Revelation took over from New Testament sweetness, which came as a relief to those of us who had had enough of his gentle Jesus, the kind that shows up at music festivals in knee-hole jeans smilingly beatifically, ready for dope and three days of love. Cohen's gospel people stalk through contemporary streets and bedrooms, so the card dealer of The Stranger Song turns out to be: "Just some Joseph looking for a manger". But every so often the more adamant Yahweh of the Old Testament shows up, bringing the year's transgressions to a mighty reckoning. A cohen is, after all, a high priest.

As seriously as he takes this persona of Satan deploring sin, it's the more inward meditations on his favourite subject - "L. Cohen" (as he styles himself at the end of Famous Blue Raincoat) - that have always drawn from him the most intensely felt and precisely visualised writing, and have challenged his melodic composition to go beyond minimalist dirge to match the force of the poetry.

Cohen's subjects in this vein of mutilated romanticism have been the usual post-Renaissance suspects: valedictions, loss and remorse, emotional cruelty (inflicted and received), the inseparability of tenderness and pain. Sometimes images, often of wistfully recollected visions - "Your hair on the pillow like a sleepy golden storm", in Hey, That's No Way to Say Goodbye - are allowed to hang in the song for the sheer metaphorical hell of it. They work so seductively they disarm the carping lit-crit who might pause to wonder if storms, unlike the lover, can actually ever be "sleepy"?

If there's just a touch too much of happy self-regard about some of those early ballads, from the mid 70s on, the onset of years Cohen saw in his musical mirror encouraged him to use imagery as building blocks in beautifully constructed, authentically poetic narratives. In the sad love triangle of Famous Blue Raincoat, Cohen transfers a garment he wore to fraying point to "my brother, my killer", who had run off with his wife, and had given her just "a flake of your life / And when she came back she was nobody's wife". In the strongest songs of this period, Cohen makes sure to skid away from self pity - "Well, my friends are gone / And my hair is gray / I ache in the places where I used to play" - into something more akin to rueful gratitude: "I'm just paying my rent every day / In the Tower of Song."

So perhaps it's not surprising that Hallelujah, the song in which music making and love making wrestle with each other, is the one most covered by other singers, and without draining the power of the piece into empty rhapsody. But to get the heartache you want from Cohen - and you know you do - you need to hear the old(ish) baffled, battle-scarred Cohen himself sing "The minor fall, the major lift", his voice falling for the forbidden Bathsheba bathing naked on the roof, where "Her beauty and the moonlight overthrew you". But nothing works out as planned. The overthrow happens as the music soars, the omnipotent sovereign-psalmist is bound and shorn, and it's from that moment, when the composing-lover is pierced to the quick, that music gets born. Hallelujah.