A level (Peter van der Merwe 1989), also "tonality level", Gerhard Kubik's "tonal step", and John Blacking's "root progression") is a temporary modal frame contrasted with another temporary modal frame built on a different foundation note. It is more general and basic than a chord and is found in Asian, African, and Celtic folk musics and in European Renaissance music. Levels then give way to chords and chord changes in Baroque music and in the twentieth-century chords give way to levels in the blues, completed with the V-IV-I progression, and spread to all popular music. (van der Merwe 1989, p.209-211)
Each level is based on one pitch, a foundation note, upon which a melodic or harmonic-melodic third, triad (fifth) (such as in the song "Shallow Brown"), or seventh (such as in the song "Donald MacGillavry") may be built. A "change" in levels is called a shift. For example, double-tonic tunes such as "Donald MacGillavry" feature shifts of level (notes: A to G) which are more emphatic than chord changes (chords: Am-G), but not as emphatic as modulations (keys: A minor to G major):
The foundation is the most important note and chords built are almost always in root position. The fifth is next in importance, and consecutive fifths are most often emphasized in shifts of level while being banned in the common practice period. The third is less important and often blue, neutral, or changing from major to minor. This last characteristic is common in the English virginalists music such as William Byrd's "The Woods so Wild" theme, which is an example of levels (F and G) being elaborated through cadence, melodic divergance from the accompaniment, and subsidiary chords, reaching a complete little cadential phrase. In the blues and blues-influenced popular music elaboration happens within the chords, as in boogie-woogie bass, which are the primary triads rather than a tone apart, and the melody also contrasts with the bassline. (van der Merwe 1989)
See also 
- van der Merwe, Peter (1989). Origins of the Popular Style: The Antecedents of Twentieth-Century Popular Music. Oxford: Clarendon Press. ISBN 0-19-316121-4.