As a music theory expert with a deep understanding of the intricacies of harmony and chord progressions, I'm delighted to delve into the concept of a secondary dominant in music. Secondary dominants are a fascinating aspect of music theory that can add depth, color, and a sense of forward momentum to a piece of music. They are a type of non-diatonic chord that serves to function as a dominant chord to a chord other than the tonic, and they are used to create tension and resolution within a piece.

In traditional tonal music, a dominant chord is a fifth interval above the tonic chord and is typically a major chord with a minor seventh added (notated as a dominant seventh chord, or V7). This chord has a strong tendency to resolve to the tonic, creating a sense of finality and closure. However, in the case of a secondary dominant, this dominant function is applied to a chord other than the tonic, hence the name.

The secondary dominant is notated as V/something, where "something" is the chord to which the secondary dominant is functioning as a dominant. For example, if we have a C major chord functioning as a secondary dominant, it would be notated as V/G if it leads to a G major chord, because in the key of C, G is not the tonic but rather the fifth scale degree.

A sequence of dom7 chords is often referred to as a chain of secondary dominants. This sequence can create a sense of harmonic movement that is both complex and intriguing. Each chord in the sequence serves as a pivot, leading to the next chord in a logical and harmonically satisfying way.

The use of a slash in the notation of secondary dominants indicates that the chord is not in root position but rather inverted, with the bass note being a different pitch from the root of the chord. This is common in more complex harmonic progressions where the root position might not provide the smoothest voice leading or the desired harmonic effect.

In popular music, there is a common practice where a secondary dominant is preceded by its predecessor, typically a II7 chord in the key of the secondary tonic. This pattern creates a smooth and familiar harmonic progression that is pleasing to the ear and is often used to lead the listener to expect a certain resolution.

For instance, in the key of C major, a secondary dominant to the G major chord (Em/G) would be D7/G. This D7 chord is functioning as a dominant to G, creating tension that resolves when the G major chord is reached. The D7 chord is built on the fifth degree of the G major scale, and it leads to the G major chord with a sense of resolution, just as a V7 chord would lead to the tonic in a more straightforward progression.

Secondary dominants are a powerful tool in the composer's or songwriter's arsenal. They can be used to create a sense of modulation, to add harmonic interest, or to lead the listener through a series of related keys. Understanding and mastering the use of secondary dominants can greatly enhance one's ability to write and analyze music that is both complex and emotionally engaging.

read more >>

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.read more >>