Secondary dominants? What’s that?, we hear you ask.
Chord V or V7 is the dominant, can other chords play the same role too?
Yes they can!
As we saw before, in the Minor Harmonic Scale the minor triad Vm was altered to a major triad; the leading note of the major scale was introduced to be able to make the strong chord change V – Im. Already in the Renaissance composers began to add more leading notes to their chord progressions in order to make such strong chord changes to every other degree of the scale. This is how the secondary dominants (S.D.), also called artificial dominants, came into being. This lesson will be about the use of these S.D.’s which are a huge enrichment of the diatonic harmony, and have been an absolute favourite of all composers since the old days.
A secondary dominant is a major triad, or dominant seventh chord, which makes a strong chord change to a chord other than I (or Im in the minor scale), and makes that chord a momentary centre of attraction. Only when it contains a major 3rd a chord can be a secondary dominant, and with a minor seventh added it is even better. To distinguish them from the real dominant the symbols for secundary dominants are placed in between brackets, and a little arrow is attached to them which points to the chord of which it is the S.D.
In the next picture all seven chords of C major are given, each preceded by its own dominant. In the first bar we see the familiar change V7 – I, with in the upper staff the two leading notes of V7 and their solutions (B to C and F to E). In bar 2 to 7 we see the other chords of C major with their secondary dominants.