Tunes of the Twenties and All That Jazz by Robert Rawlins

This has created a market for lead-sheet versions of standards, intended for improvisers. Since the 1960s, jazz education, once nearly non-existent, has become widespread. Early, illegal fake books used this format as well. When jazz musicians of the 1940s (and later) wrote their own tunes, they probably would have used lead-sheet format, notating the harmonic accompaniment with chord symbols, rather than with a piano arrangement. In the early 1940s, a commercial product called “Tune-Dex Cards” presented songs with just melody and chord symbols, suggesting a general acceptance by musicians of what we now call “lead sheet” format. Jazz musicians have always tended to reduce song arrangements to a basic harmonic framework, in order to create the space needed for improvisation - and chord symbol notation would have helped them to do this. Beginning around 1930, chord symbols were often also provided, for guitarists and for pianists who did not read music well enough to play the written-out accompaniments.

Until approximately the 1960s, songs were marketed in print form primarily as sheet music, including a composed piano accompaniment. Over the last century or so, this harmonic vocabulary has evolved into a set of practices that is ideally suited to the needs of contemporary jazz performers. The basic harmonic vocabulary of jazz standards derives from “common practice” classical music, but is adapted to fit the short forms (usually 12, 16, or 32 measures) of popular songs. By Peter Spitzer - Jazz Author, Musician, and Instructor

Tunes of the Twenties and All That Jazz by Robert Rawlins