Suomeksi | In English

Secondary dominants

In connection with the dominant and predominant chords we discussed the meaning of the tritone as a tension-building ("dominant") interval. To recognize a key by ear, it is enough to hear the tritone resolve into either a major or a minor chord.

A major or minor triad can build on a variety of degrees of a key and sound "like the tonic" if preceded by its dominant chord. An example of this is the second degree chord (Dm) in C major preceded by A7 (V7 in D minor): the relationship between these chords is stronger than in the ordinary progression VI-II (Am-Dm). This is due to the tritone resolution: the third and seventh of A7 resolve into the root and third of Dm.

The dom7 always includes a tritone; since a major key only includes one tritone, secondary dominants always include altered notes.

The symbol for a secondary dominant is the dominant chord sign (V, Vs, or VII) followed by a slash (/). The slash is followed by the scale degree (secondary tonic) into which the secondary dominant resolves.

In the example below, we see the secondary dominant chords in C major with their secondary tonics (root + third) with scale degree symbols and absolute chord signs. A diminished triad, the VII degree does not have a secondary dominant (or the II degree of a minor scale).

The tritone resolutions of the same chords with consequent chromatic alterations are seen below:

If a minor third is added in the tritone, the result is a secondary dominant of the VII type. If another third is added on top of the tritone, the result is a secondary dominant of the VII7 type, which is a diminished four-note chord. A diminished chord includes two tritones; their proper resolution is shown in the example. While the diminished chord includes two tritones demanding resolution, the dominant type (V7/) secondary dominant is the most common because it builds a fourth relation to the secondary tonic.

In a minor key, some chords can be written in the following two ways (if we do not stick to the chord structures of the harmonic minor):
V/VI = III (in A minor, C major is also the dominant for F major)
V/III = VII (G is the dominant for C)
Therefore, relative keys share a number of chords (see the example below). Chord progression Am – Dm – G7 – C can be perceived as the A minor degrees I – IV – VII7 – III or I – IV – V7/III- III. The same chords in C major are VI – II – V7 – I (see Progression by fifths).

Even if the first chord is not dom7 or a diminished four-note chord, a fourth relation in consecutive chords tends to refer to a dominant structure. The tonic chord of a major key could also be written V/IV. What is essential is to recognize a fourth relation even if it is not written (for example, III-VI-II-V). The difference between a predominant (for example, II degree) and a secondary dominant (V/V) is smaller than what the symbols give reason to expect. In jazz chord analysis, the following symbols are used: II7 = D7 and IIm7 = Dm7 (in C major).

Voice leading and secondary dominants

Secondary dominants sometimes deviate from the traditional voice leading rules. For example, with V7/V, it is common to lower the augmented fourth degree if the chord progresses to dom7. This causes a parallel motion by tritones (bar 1).

V/V is a widespread chord; that is why the fifth degree of a key is rarely diminished – the V/V chord requires a major third, and 5 would not be perceived as part of the chord.

Tritone resolutions and #4 are associated with other secondary dominant chords as well (bars 2-4). Bars 5-7 display typical middle-part voice leadings in connection with the chords mentioned.

When secondary dominants are in first inversions, the chromatic alteration happens in the bass, which intensifies the dominant nature of the chords. A ninth chord can also be a type of secondary dominant, like all variants of dom7, including altered notes (see Absolute chord symbols).

A progression by fifths is a progression of diatonic chords by fifths. They are often four-note chords with m7 and the tritone as a dominant interval.

A sequence of dom7 chords is called a chain of secondary dominants. A slash is applied in the symbols until a diatonic chord appears in the chain.

In popular music, it is customary that a secondary dominant is preceded by its predominant, typically a II7 in the key of the secondary tonic. The degree sign for the secondary subdominant can be added to the secondary dominant chord with, for example, a bracket.

A diatonic secondary subdominant is not written, but its function is worth noting. For example in the progression C - Am - D7 - G7 – C, Am is the II chord of the dominant key.