Today while teaching my Jazz Theory & Aural Skills class at DU,
I had a revelation – a way of explaining the notion of
“secondary dominant” chords by appealing to concepts and
terminology from the TV show “Downton Abbey” (or substitute your
favorite show, movie, or book about British aristocracy). Sound
far-fetched? Read on. As many musicians know, “most” chords in
“most” songs are diatonic, meaning they consist exclusively of
notes that are in the key. So in the key of C, we expect to see
C, Dmi, Emi, F, G, Ami, and Bdim chords as triads, or Cma7,
Dmi7, Emi7, Fma7, G7, Ami7, and Bmi7b5 as seventh chords, since
these chords consist of notes from the key of C. We often label
these chords with Roman numerals: I, ii, iii, IV, V, vi, and
viiø. But most songs also include at least a few chords that are
not diatonic – chords that include at least one note not in the
key. The majortiy of these non-diatnoic chords fall into a few
basic categories that explain the function of the chord, and by
far the most important s