Secondary dominant

Secondary dominant (also applied dominant, artificial dominant, or borrowed dominant) is an analytical label for a specific harmonic device that is prevalent in the tonal idiom of Western music beginning in the common practice period. In the tonal idiom, a song or piece of music has a tonic note and chord, which is based on the root of the key that the piece is in. The most important chords in a tonal song or piece are the tonic chord (labeled as I in harmonic analysis) and the dominant chord (V). In the key of C major, the tonic chord is C major and the dominant chord is G.

A secondary dominant refers to a dominant triad or seventh chord set to resolve to a degree that is not the tonic, with V(7)/V (V[7] of V), the dominant of the dominant, being the most frequently encountered example. The chord a secondary dominant progresses to can be thought of as a briefly tonicized chord; that is the chord that the secondary dominant resolves to, which sounds momentarily like a tonic to the listener. Tonicizations longer than a phrase can be regarded as modulations to a new key (or new tonic).

"The purpose of the secondary dominant is to place emphasis on a chord within the diatonic progression." "Functioning secondary dominants are used when a composer wants to inject a greater feeling of movement into a diatonic progression." The secondary-dominant terminology is still usually applied even if the chord resolution is nonfunctional (for example, the V/ii label is still used even if the V/ii chord is not followed by ii).

The major scale contains seven basic chords, which are designated in harmonic analysis with Roman numerals in ascending order. Since the chord on the seventh scale degree is a diminished triad, it is not considered stable, and so only the other six chords may be treated at temporary tonic chords, and so be eligible for an applied dominant. In the key of C major, those six chords are:

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