Collegiate instruction in jazz improvisation is typically given in two places: the jazz theory classroom and private lessons. In both contexts, one of the first concepts taught is the relationship between chord and scale. I distinguish the term "scale" in the classical sense from the term "chord scale." The former refers to a stepwise collection of pitches that expresses a tonal center. The latter refers to a stepwise collection of pitches that melodically expresses a chord. A harmonic progression contains all of the pitches in a major scale, and the progression could easily support a melody that expresses all of the pitches of that scale. Classical theory holds that one scale accounts for the harmonic and melodic organization of the whole progression. By contrast, jazz pedagogy recognizes a succession of "chord scales," one for each chord. Chord-scale theory teaches students to make harmonically informed melodic improvisations by enforcing one-to-one relationships between chords and scales.
"Beyond Chord-Scale Theory - Realizing a Species Approach to Jazz Improvisation,"
Journal of Music Theory Pedagogy: Vol. 21, Article 5.
Available at: https://digitalcollections.lipscomb.edu/jmtp/vol21/iss1/5