Guide tone lines are single lines which are developed by the voice leading of the essential chord tones and guide the listener through the chord progression. The essential (guide) tones are the root, third (or fourth on sus4 chords), and seventh (or sixth on 6th chords). These pitches make each chord sound major versus minor, and the major or minor seventh further defines the chordal sound.

Individual guide tone lines may be one of three configurations: either one of the two lines created from previous process or a combination of the two lines from the voice leading process:

References

"Harmony 2" by Barrie Nettles, Berklee College of Music, Boston, 1987, page 26