A major triad or Mm 7th chord with a secondary dominant function lies a perfect 5th above some pitch in the key other than the tonic. The note a perfect 5th below the root of the secondary dominant serves as a temporary tonic for the purpose of analysis. This tonicized pitch acts as a tonic to the secondary dominant chord, which may also be referred to as an applied dominant. When diatonic minor chords in a major key (ii, iii, and vi) are altered to become major chords with an accidental raising the 3rd, they usually function as secondary dominants. This is confirmed if the chord that follows is down a P5th.
It is analyzed as “V of x”, and the x can represent any diatonic pitch in the key. A slash is used to show the relationship between the chords. In the key of C major, ii = D minor, and V/ii = A major, a P5 above the note D. The C# used to raise the 3rd of the diatonic minor triad built on A is the leading tone in the key of D. The raised 3rd of the secondary dominant is always a half-step below the tonicized pitch.
The most common secondary dominant chords in the key of C major are V/ii = A major; V/iii = B major; V/V = D major; and V/vi = E major. These relationships are common to all major keys. The leading tone chord, viio, is not tonicized because of the instability of the diminished chord.
In general, a diatonic chord in a major key that would ordinarily be minor with a raised 3rd can usually be analyzed as a secondary dominant. The exception to this rule is the V7/IV chord. This Mm7th chord is built on the tonic pitch, and the chromatic alteration is a lowered 7th in the key. In this case the secondary dominant chord contains a lowered pitch rather than a raised 3rd, and it is always built on the tonic of the key. The quality of a Mm7th chord dictates that it can only be analyzed as a V7, and not as a tonic function.
Given a scale degree, consider that note the tonic of the key to which the secondary dominant belongs. Determine the dominant, or V7 chord in that key, and spell it accordingly. The upper or lower case Roman Numeral to the right of the slash indicates the major or minor quality of a triad built on that scale degree in a key. Let’s apply this information to spell the V7/III chord in the key of A minor. The mediant, or III chord is C major, and it’s dominant is G7 (G-B-D-F). A figured bass symbol may be included to invert the chord.
Secondary dominant chords most often resolve to the chord built on the tonicized note. However, it is common to see chains of secondary dominants in a circle of fifths progression. This sequence of chords in C major might consist of E7 – A7 – D7 – G7 – C, analyzed in Roman Numerals as V7/V7/V7/V7/I.
In jazz and popular music the ii7 – V7 sequence is often used to tonicize any diatonic or non-diatonic chord. This is referred to as a “two-five of” the following chord. These two-fives are sprinkled generously throughout most jazz reharmonizations. They often do not resolve to the tonicized pitch, and may be found in a cycle of downward 5th or downward 2nd progressions.
Resolve each note according to its tendency, or chromatic inflection. Raised pitches continue upwards, as a general rule, and lowered pitches move down. The altered major 3rd of the secondary dominant chord resolves up by half-step. The minor 7th of the Mm7 chord typically resolves down by half-step.
Secondary Dominant Examples