Secondary Dominant Chords
Secondary dominant chords are “V of __” Chords. When using roman numerals, secondary dominants are spelled out using slashes. For example, you might see a V/V. This tells you to play the major chord that is five scale degrees above the dominant chord. In the key of C major, this translates to mean D major and G major, respectively; D is a perfect fifth above G.
Secondary dominant chords do not work well when paired with the seventh (leading tone) scale degree. This is because the seventh scale degree forms a diminished triad, which is highly unstable. The secondary dominant should also never be associated with a I or tonic chord since the V of I is a primary dominant chord.
Secondary dominant chords are not limited to V chords. FIGURE 6-16 shows you all of the secondary dominant chords you may use to spice up your chord progressions. In addition to V/V, you will see V/ii, V/iii, V/IV, and V/vi chords. In order to allow these chords to flow smoothly from one to the next, inversions have been used.
FIGURE 6-16: Secondary Dominant Chords
Inversions allow each chord to flow easily into the next.
Secondary dominants are interesting passageways between two diatonic triads. This is illustrated in FIGURE 6-17. Here, a V of ii spices up a simple I-ii-V7-I chord progression.
FIGURE 6-17: Secondary Dominant Chord Progression