Jazz improvisation is inherently subjective. What makes one solo “better” than any other is often a matter of taste, a preference for a given style. But while articulation, swing feel, and phrasing vary wildly from one great player to the next, every noteworthy improviser is able to effortlessly demonstrate a tune’s chordal movement. Just as any writer worth her salt showcases complete mastery over grammatical convention, the conversant jazz musician must be fully in command of the harmonic structure on top of which they are improvising. Simply put: You’ve gotta be able to play the changes!
Arguably even more important than their virtuosic technique and impeccable rhythmic feel, what makes the great players truly great is their unshakable fluency of harmonic language. Until you are playing all the changes over a tune, your not really playing the tune. All the cool licks in the world won’t make you sound any more proficient than a truckload of glue will convince anybody that little Tommy’s mustache is a all-natural, glorious Tom Selleck.