'In Miles Davis's hands, modernism wasn't an aesthetic concept at all. It was his way of life'

Op Art was the thing in December 1965. Earlier in the year the Museum of Modern Art in New York had mounted an Op-exhibition entitled The Responsive Eye, while autumn's art schedules in the UK had been mildly perked by a cross-media show at the ICA called Between Poetry and Painting, which featured, inter alia, Op Art and words in boggly tension. Modernism was speeding up. It had come indoors from the abstruse outlands of Abstract Expressionism and trolleyed up the aisles of pop culture. Squiggles, checks, whorls and spirals, "things that drive you mad when you look at them" - Op's visual currency was self-consciously revolutionary, got much of its texture from the patterns of commerce and depended entirely for its effects on optical illusion. It was a fix. Which is another way of saying that it was fun while it lasted.

Meanwhile, at modernism's other sharp ends, John Coltrane was disappearing under full sail up a blind creek, and tower blocks were going up in Peckham. You could argue that by the mid-Sixties the modernist idea had done its job and gone out to lunch on the proceeds.

Which just goes to show that you should never rely on isms to know where you are. If, in December 1965, you'd been au fait with Miles Davis for the past decade or so, you'd have become accustomed to the modernist ideal as a cogent and graceful thing expressed with absolute attention to those elements of style which give art purchase on the real world. In Davis's hands, modernism wasn't an aesthetic concept at all. It was his way of life.

All of which is a roundabout way of saying that Davis always saw the big picture, culturally, aesthetically, sensually and socially. That's what made him a great leader as well as top player and icon of cool. And if ever there was a single, lucent document of Davis's accomplishment as leader and practical modernist then it has to be this extraordinary episode, released in its entirety for the first time since its first furtive appearance in Japan in severely truncated form nearly two decades ago.

The Complete Live at the Plugged Nickel, recorded at the Chicago nightclub over two long nights that December, is the nearest we'll ever get now to living Davis's life with him as it happened - fluffs, repetitions, hesitations, glorious epiphanies and all. It's just brief enough - at upwards of seven hours - to be read as a jointed single statement but long enough to make you feel that you're tackling something more substantial than edited highlights.

This eight-CD set is, to all intents and purposes, a slice of real time, and as such it presents an unusual challenge to the listener: not only to time his toilet-breaks with consideration but to engage with the music on a tough basis: without expectation of the organised intimacy that breeds so amiably over the brief, unitary length of conventional albums. You either live the life of the Plugged Nickel as it happens or not deal with it at all. It's possible that your life might be too short.

Which would be a shame, because the Plugged Nickel sets caught Davis's "second great quintet" at a moment of real ignition, at the mid-point between the recording of the beautiful ESP and the torrid Miles Smiles.

Davis's own playing is perhaps not as clear and authoritative as it had been on the My Funny Valentine date the previous year but both his and the new group's language has vaulted into new dynamic territory. Davis's concept of "time - no changes" here is not just a theoretical solution to the problem of how to find freedom in regulated musical space. It's a way to make the shape of music absolutely plastic, without losing its hard, defining edge. The defining sharpness of modernity.

Saxophonist Wayne Shorter is incredible throughout: garrulous, meteoric, bloody and, occasionally, really quite funny. Modernism, to him, must have seemed like life with the brightness turned up. Not a bunch of squiggles to drive you mad but a continuation by other means of the impulse to be real. The set will cost you between pounds 80 and pounds 100, incidentally.