Laugh if you like, but these dark arts persist

The best ever blurb came from the immortal Groucho Marx. He wrote, apropos of his friend S J Perelman's first collection of articles, "From the moment I picked your book up until I laid it down I was convulsed with laughter. Someday I intend on reading it."

Lesser beings can only dream of such an endorsement. However, the curious underworld of the pre-publication blurb – a dark art pitched somewhere between the friendly back-scratch and the market trader's shout – persists despite decades of ridicule. You might think writers secure in their eminence would refuse offers to boost younger would-be rivals. Yet for whatever motive – passion, a sense of duty, the urge to be seen with fingers on the pulse – even inaccessibly great authors still cry out the literary equivalent of "One Pound Fish".

With the more reclusive superstars, the decision to blurb becomes an event in itself. The South African Nobel laureate J M Coetzee refuses all interview requests and steers clear of publishing's social scene. Yet he regularly blurbs for promising newcomers, saving his public warmth for the jacket shout-line. Or take Thomas Pynchon, the invisible emperor of American fiction. Among his incredibly rare public pronouncements are two dozen-odd jacket blurbs, often bestowed in unexpected places. Such as, in 1998, the cover of a book by a British debut novelist who worked as bus driver: Magnus Mills's The Restraint of Beasts. The unseen icon called it "a demented, deadpan comic wonder". He was right.

With beginners, publishers may over-egg the jacket pudding with too many blurbs but when writers achieve genuine distinction, less becomes more. This autumn Edna O'Brien published her memoirs, Country Girl, after 60 years of authorship during which she has known, and been admired by, almost everyone. On her cover, however, advance praise came from just one writer: as much a tribute to the blurber as to the blurbee. Who was her sole cover-line champion? It had to be Philip Roth.