Today I'll write a bit about secondary dominant chords, which are also called applied chords in some textbooks. Secondary dominants temporarily make the chord that comes after them sound like a tonic, albeit briefly. We call this phenomenon tonicization. Very often, you'll see secondary dominants at cadence points as a method of intensifying the forward motion to the cadence.
Any major or minor diatonic triad can be preceded by its secondary dominant. Diminished triads (viio in major and iio in minor) cannot be tonicized because they cannot serve as the tonic chord in any key.
Secondary dominant chords come in several shapes and sizes. Most commonly, perhaps, is the secondary dominant seventh chord. One can have a secondary dominant triad, but if the purpose of the chord is to intensify the motion to the next chord, the chordal seventh in conjunction with the leading tone really drives the progression forward. Secondary dominants also include chords built on the leading tone, like viio, viio7, and their half-diminished brethren. When I say secondary dominants, I'm using "dominant" in the broader sense--that is, I'm referring to dominant-function chords.
One of the most commonly encountered secondary dominant chords is the dominant of the dominant. To determine what this look like, let's first find the dominant of C major, which is G. The dominant of the dominant will have a root that is five diatonic steps above the root of the dominant: in this case, the root of the dominant of the dominant is D. We also need to find the leading tone that will propel us to the dominant chord. In this case, the leading tone to G is F#. Notice that F# is not in the key of C major. We'll need to be sure to add this accidental in our exercises. To round out the chord, we need to construct a major-minor (dominant) seventh chord using D as the root and F# as the third. An A and a C complete the chord. We would label this chord V7/V, indicating that it is the dominant seventh of the dominant.
The same resolution tendencies apply to secondary dominants that apply to ordinary dominants. The chordal seventh must resolve down; the leading tone must move up by step to the "tonic," unless it's in an inner voice in which case it can leap down to the fifth of the following chord. It may help you to think about resolution in terms of complete/incomplete chords: usually, either the V chord or the I chord must be incomplete in order to avoid parallels and obey the resolution tendencies.
As I said earlier, any triad can be preceded by its secondary dominant. We can find V/iii chords, or V7/IV chords using the same method detailed above. The chords would then be labeled accordingly.
A few helpful pointers:
If I have time, I'll add some score examples later. Stay tuned!
Any major or minor diatonic triad can be preceded by its secondary dominant. Diminished triads (viio in major and iio in minor) cannot be tonicized because they cannot serve as the tonic chord in any key.
Secondary dominant chords come in several shapes and sizes. Most commonly, perhaps, is the secondary dominant seventh chord. One can have a secondary dominant triad, but if the purpose of the chord is to intensify the motion to the next chord, the chordal seventh in conjunction with the leading tone really drives the progression forward. Secondary dominants also include chords built on the leading tone, like viio, viio7, and their half-diminished brethren. When I say secondary dominants, I'm using "dominant" in the broader sense--that is, I'm referring to dominant-function chords.
One of the most commonly encountered secondary dominant chords is the dominant of the dominant. To determine what this look like, let's first find the dominant of C major, which is G. The dominant of the dominant will have a root that is five diatonic steps above the root of the dominant: in this case, the root of the dominant of the dominant is D. We also need to find the leading tone that will propel us to the dominant chord. In this case, the leading tone to G is F#. Notice that F# is not in the key of C major. We'll need to be sure to add this accidental in our exercises. To round out the chord, we need to construct a major-minor (dominant) seventh chord using D as the root and F# as the third. An A and a C complete the chord. We would label this chord V7/V, indicating that it is the dominant seventh of the dominant.
The same resolution tendencies apply to secondary dominants that apply to ordinary dominants. The chordal seventh must resolve down; the leading tone must move up by step to the "tonic," unless it's in an inner voice in which case it can leap down to the fifth of the following chord. It may help you to think about resolution in terms of complete/incomplete chords: usually, either the V chord or the I chord must be incomplete in order to avoid parallels and obey the resolution tendencies.
As I said earlier, any triad can be preceded by its secondary dominant. We can find V/iii chords, or V7/IV chords using the same method detailed above. The chords would then be labeled accordingly.
A few helpful pointers:
Secondary dominants will almost always require at least one accidental, usually applied to the leading tone.
Secondary dominants may resolve deceptively. I'm not going to get into that in this post for various reasons. Consult your local theory textbook for more information.
The vast majority of pedagogical approaches do not allow for things like ii/III or VI/VI. If your "numerator" (the Roman numeral above the line) is not V, V7, viio, or viio7, it's most likely incorrect.
When writing a V/IV (in major or minor) be sure always to use a V7 chord. The dominant of the subdominant is equivalent to the tonic chord. The added seventh will distinguish the chord from a plain vanilla tonic triad.
You might wish to think of secondary dominants as substitutes for their diatonic partners. A V7/V chord will stand in for a ii chord, and it actually looks quite a lot like it: D F# A C vs. D F A in C major. A V7/IV chord looks like a I chord; a V7/vi looks like a iii, etc.
If I have time, I'll add some score examples later. Stay tuned!