Strange Changes

A central aspect of jazz practice is harmonic substitution, where a functionally related chord of a different flavor displaces, or is superimposed upon, another. These substitutions can be predetermined, as in an arrangement of a jazz standard, or effected “in the heat of the moment,” as ensemble members carve alternative harmonic paths through the “changes” of the tune. Aspects of harmonic substitution, or reharmonization, are addressed elsewhere in this issue. In this essay I will outline a related and, I suggest, foundational practice that can be used as a model for thinking about harmonic substitution: a number of common harmonic progressions built into the structure of the tunes themselves. In other words, the very notion of carving alternative paths toward harmonic goals is already built into the structure of the songs being elaborated upon by jazz musicians. These practices relate to and extend the concept of mode mixture, well-known in conventional music-theoretical discourse.