When Miles Davis came to New York in 1945, at the age of 19, he replaced Gillespie as Parker’s trumpeter for a few years and played very much in their style. A decade later, he, too, was wondering what to do next.

The answer came from a friend of his named George Russell (who died just last month at the age of 86). A brilliant composer and scholar in his own right, Russell spent the better part of the ’50s devising a new theory of jazz improvisation based not on chord changes but on scales or “modes.” The kind of music that resulted was often called “modal” jazz. (A scale consists of the eight notes from one octave to the next. * A chord consists of three or four specific notes in that scale, played together or in sequence: For instance, a C chord is C-E-G.)

This distinction may seem slight, but its implications were enormous. In a bebop improvisation, the chord changes (which occur when, usually, the pianist changes the harmony from one chord to another) serve as a compass; they point the direction to the next bar or the next phrase. Chords follow a particular pattern (that’s why it’s easy to hum along with most blues and ballads); you know what the next chord will be; you know that the notes you play will consist of the notes that comprise that chord or some variation on them. Playing blues, you know that the sequence of chord changes will be finished in 12 bars (or, if it’s a song, 32 bars), and then you’ll either end your solo or start the sequence again.

Russell threw the compass out the window. You could play all the notes of a scale, which is to say any and all notes. “It is for the musician to sing his own song really,” Russell wrote, “without having to meet the deadline of a particular chord.” In other words, he continued, “you are free to do anything” (the italics were his), “as long as you know where home is”—as long as you know where you’re going to wind up.

One night in 1958, Russell sat down with Davis at a piano and laid out his theory’s possibilities—how to link chords, scales, and melodies in almost unlimited combinations. Miles realized this was a way out of bebop’s cul-de-sac. “Man,” he told Russell, “if Bird was alive, this would kill him.”

In an interview that year with critic Nat Hentoff, Miles explained the new approach. “When you go this way,” he said, “you can go on forever. You don’t have to worry about changes, and you can do more with time. It becomes a challenge to see how melodically inventive you are. … I think a movement in jazz is beginning, away from the conventional string of chords and a return to emphasis on melodic rather than harmonic variations. There will be fewer chords but infinite possibilities as to what to do with them.”

Davis needed one more thing before he could go this route: a pianist who knew how to accompany without playing chords. This was a radical notion. Laying down the chords—supplying the frontline horn players with the compass that kept their improvisations on the right path—was what modern jazz pianists did. Russell recommended someone he’d hired for a few of his own sessions, an intense young white man named Bill Evans.

Evans was conservatory-trained with a penchant for the French Impressionist composers, like Ravel and Debussy, whose harmonies floated airily above the melody line. When Evans started playing jazz, he tended not to play the root of a chord; for instance, when playing a C chord, he’d avoid playing a C note. Instead, he’d play some other note in, or hovering around, the chord, suggesting the chord without locking himself into its restraints.

The late great Nat Henoff did the liner notes for this masterpiece.

The other key album is Miles Davis’ Kind of Blue (Columbia CT 1355). Davis, thoroughly impatient with writing that ties him to thick chordal backgrounds, wants “fewer chords but infinite possibilities as to what to do with them. When you go this way, you go on forever. It becomes a challenge to see how melodiously inventive you are.” Davis has rarely if ever given himself and his men so much extended melodic freedom as in his new album; and the pieces—all by him—are remarkably evocative of endless melodic distances. Deceptively simple in construction, they provide a spare but resiliently firm lifeline that allows the soloists to plunge into introspection without losing the shape of the whole. Two especially, All Blues and Flamenco Sketches (whose titles are reversed in the notes and on the record) are hypnotically absorbing. Miles now writes more and more the way he prefers to play, and he is likely to influence jazz composers as thoroughly as he already has many jazz instrumentalists.

So sit back and have a listen, get yourself an adult beverage because the adults are in charge again!.