Understanding Secondary Dominant Chords in Music Theory

Introduction to Secondary Dominants

Secondary dominant chords are a fascinating and versatile tool in music theory and composition. These chords play a key role in modulating key centers and enhancing the harmonic structure in a piece of music. Let's explore how to read and understand secondary dominant chords effectively.

Identifying the Key

To begin with, it's crucial to identify the key in which you are working. For example, if you are in the key of G major, the tonic (I) is G. Understanding the key signature is essential for interpreting chords and their functions.

Three and Four Note Chords in G Major

In the key of G major, the three note chords are:

G major (G, B, D) A minor (A, C, E) B minor (B, D, F#) C major (C, E, G) D major (D, F# , A) E minor (E, G, B) F# diminished (F#, A, C)

The four note chords include:

G major 7 (G, B, D, F#) A minor 7 (A, C, E, G) B minor 7 (B, D, F# , A) C major 7 (C, E, G, B) D7 (D, F#, A, C) E minor 7 (E, G, B, D) F# half diminished (F#, A, C, Eb)

Secondary Dominant Explained

A secondary dominant chord is formed when the 5 chord (V7) of a certain chord becomes the new temporary tonic, thus resolving to a new key center. For instance, in the key of G major, the V7 chord is D7. If D7 resolves to G minor, then D7 is a secondary dominant chord - it is the dominant of the V chord (A7) which then resolves to the original tonic (G).

Functional Role of Secondary Dominants

Secondary dominants are often used to create tension and resolve to another tonic. They typically resolve to a chord that is a dominant of the new key. For example, in the key of F major, a D7 chord resolving to G minor would classify as a secondary dominant. The D7 chord is the dominant of the next V (G) chord in the new key.

Common Secondary Dominants

Secondary dominants often have roots that are no more than three or four steps away from the dominant of the key along the circle of fifths, typically moving in the sharp direction. Common secondary dominants in the key of C include D7, A7, E7, and B7. The dominant chord rooted on the tonic of the key itself is also frequently used, such as C7 resolving to F major.

Key Progression Example: C Major

A typical chord progression that showcases the use of secondary dominants is the II V7 I progression. Here, the Dm7 G7 C progression features two secondary dominants: C A7 D7 G7 C.

How to Identify Secondary Dominants

The easiest way to identify a secondary dominant is to determine the temporary tonic you want to establish and then look to the chord that is a fifth above. For instance, if the temporary tonic is G in the key of C, the secondary dominant would be D7.

Common Secondary Dominant Forms

A common secondary dominant is the V/V form, which means the fifth of the fifth (dominant of the dominant). In the key of C, instead of using Dm, you would use D major (D) which resolves to G (the dominant of C). Similarly, in the key of G, instead of A minor, you would use A major (A) which resolves to D.

Conclusion

Mastery of secondary dominant chords is a valuable skill for musicians and composers. By understanding the techniques and functions of these chords, you can create richer, more complex harmonic progressions in your compositions. Whether you are working within a specific key or exploring new tonalities, secondary dominants add a layer of nuance and depth to your music.