Jazz musicians often use different harmonic substitutions to modify the content of diatonicprogressions. The most common harmonic modifications of the Imaj 7 –vi 7 –ii 7 –V 7progression involve the use of secondary dominant chords (V7/X), and tritone substitutions(TR/X 7). Figure 13.5 demonstrates these substitutions using Model III of harmonicrealization.The secondary dominant 7ths A7 and D7 are analyzed with two different Roman numerallabels VI7 and V 7/ii, and II 7 and V 7/V, which can be used interchangeably. The tritonesubstitutions, E≤7 and D≤7, also use two Roman numerals, ≤III7 and TR/VI7, and ≤II7and TR/V7, respectively