Any major, minor, or dominant triad, and its extended forms, can be preceded by its own secondary chord.
The types of secondary chords which can be used are:
- The dominant
- The dominant seventh
- The diminished
- The diminished seventh
and preceding major chords only,
- The half diminished seventh
Looking at example 1 we see the familiar chords common to all harmonised major scales
Leaving out the seventh degree (as it’s a diminished triad), we can precede each of the six remaining triads by their own dominants, see Example 2
As you can see, the secondary dominant which precedes the relevant triad is the same as you would find in the actual key of that triad. For example, the initial D dominant is simply chord V* in the key of G major (this is not a secondary dominant as it is simply V in the key of our example), the E dominant which precedes chord ii in G major – A minor, is a secondary dominant and is the dominant of A minor. The G sharp, which is its third, is not found in the key of G major, see Example 3
Likewise the F sharp secondary dominant preceding chord iii in G major – B minor, is the same dominant as you would find in the key of B minor. As with these examples, any additional accidentals found in the key of the secondary chord must be included.
The G chord preceding chord IV in G major – C major, can be treated as a secondary dominant when a seventh is added. In the current example the G chord preceding chord IV simply sounds like chord I moving to chord IV and so is not a secondary dominant.
* Roman numerals are often used when referring to scale degrees of a key. They will be used throughout this site.
Secondary Dominant Sevenths
Our secondary dominants from the previous section can all have sevenths added, creating dominant seventh chords. The C chord in the previous section can now be preceded by a secondary dominant seventh, see Example 4
Note the F natural which has been added to the G dominant seventh preceding chord IV – sometimes the key signature must be cancelled when using secondary chords.
Secondary diminished chords behave like secondary dominants and dominant sevenths; they are also taken from the key to which the relevant chord belongs. The secondary diminished chords are, however, found on the seventh degree of the key whereas the dominants are found on the fifth, see Example 5
Example 6 precedes our G major triads with secondary diminished chords.
Note: Diminished chords are generally used in first inversion. In this example they are in root position to show the semitone rise of the leading note to the root of the relevant triads. See Voice Leading for more information regarding the use of diminished triads in first inversion.
Secondary Diminished Sevenths
As with the secondary dominants, the secondary diminished chords can have sevenths added.
Note the relevant accidentals which are added to make these chords fully diminished – the diminished seventh is constructed from stacked minor thirds, unlike the half diminished seventh.
Half Diminished Sevenths
Major triads may be preceded by secondary half diminished seventh chords. The half diminished seventh is constructed by two minor thirds and a major third
Half diminished sevenths can only precede major chords as they are the diatonic seventh chord found on the seventh degree of a major scale. See Example 8