Harmonic substitution—Harmonic substitution consists of changing the qualityof a chord, that is to say altering one or several notes of the infrastructure. Themost common use of this rule produces secondary dominants: in sequencesbased on fifth relations expressed by functional degrees (I-IV-vii-iii-vi-ii-V-I),this consists of transforming any of the chords preceding V (except IV), that isto say either vii, iii, vi, or ii (all chords with minor thirds) into a seventh chord: