Oh, my God! They have killed cool

In what may well have been his sole known interesting utterance, John Travolta once denied being cool. On the other hand, he added, he was better at acting cool than anybody else in the world. It's a shame this piercing aperçu was unavailable to Dick Pountain and David Robins when they were devising Cool Rules - is the title an adjective followed by a noun, or a noun followed by a verb? - for it tells us a great deal about the recent history of this most desirable and nebulous of qualities.

In what may well have been his sole known interesting utterance, John Travolta once denied being cool. On the other hand, he added, he was better at acting cool than anybody else in the world. It's a shame this piercing aperçu was unavailable to Dick Pountain and David Robins when they were devising Cool Rules - is the title an adjective followed by a noun, or a noun followed by a verb? - for it tells us a great deal about the recent history of this most desirable and nebulous of qualities.

This slim but dense volume, packaged in a cool blue and adorned with a photo of James Dean, is the work of two veterans of the left-political wing of the Sixties underground. It explores the essence of cool and how it remains constant as fashions shift and the more perishable "hip" is forced into a continual process of redefinition to avoid deliquescing into its polar opposite - "naff". A defining aspect of cool is that it prefers to recognise itself rather than explain itself. It is therefore an act of profound cultural courage to set out out to explain and define cool.

The authors dispose in short order of two superficial definitions. One is calm unflappability, as in "keeping one's cool" or being a "cool customer". The other is a non-specific indicator of approval - "that's cool" - which can mean anything from "brilliant" to a shrugging "yeah, sure, whatever".

True "Cool" - capitalised by the authors to indicate its underlying substance - may shift its surface characteristics (other than the eternal sunglasses-after-dark). But its fundamental nature is constant. It is this ur-cool that Pountain and Robins seek to anatomise, and anatomise it they do. Its history takes in everything from sprezzatura, the sang froid of Renaissance princes, to the ironic deference, barely masking stoic defiance, of those who had unwillingly become African-Americans and of such icons as Brando and Brecht, Bogart and Bacall, Dean and Dietrich, Keith Richards and Billie Holiday.

Cool is where self-possession blurs into self-obsession. It's where sang froid flirts with callous numbness. Cool knows when institutionalised sentimentality should be countered with dry-witted reserve; and also when a puritanical culture should be confronted with passionate and authentic expression. Most of all, it knows - as did so many of the great jazz, soul and rock performers venerated for their uncorrupted cool - when and how to combine the two.

In political terms, cool is bad news for both right and left. It embraces economic and social laissez-faire, sharing the far right's mistrust of governmental spying and meddling, but not its moralism. Cool is "by preference apolitical, but if forced to take sides will usually side with the more libertarian option, which may be on the left or right in different historical contexts. There is a sense in which Cool is the inverse of Fascism, which embraces precisely the opposite combination - repressively conservative social policies with corporate economics." Which may explain why Tony Blair will never be cool, no matter how many Stratocasters and Gallaghers he may pose with; and why Bill Clinton, no matter how reactionary his policies or weasely his behaviour, is.

This side of the millennial divide, cool is, so to speak, on ice. Cool has gone cold because its superficial characteristics have been so profoundly embraced by the market, that it has run, shades first, into the cultural paradox of mass bohemianism. If everybody's cool - and, these days, anybody prepared to pore over a style bible and make a few key purchases can consider themselves cool-ish - then nobody's cool. If cool can be bought, it in effect barely exists.

Cool may not be dead, but it is battery-farmed and neatly packaged. Commodification has come closer to exterminating cool than any "just say no" campaign could. Until it awakens from its Arthurian slumber, Pountain and Robins have provided cool with an appropriately elegant headstone.

The reviewer's biography of the ultra-cool John Lee Hooker is published by Penguin