A harmonic modulation is the process of changing tonal centers. Consistent use of accidentals in a new key followed by a cadence confirms the sense of a new tonal center. A change of mode from major to parallel minor is not a modulation, because the tonal center is the same. A move between relative major and minor keys is a modulation, because they have different tonal centers. Modulations may be very abrupt, or they may unfold so gradually that they are barely noticeable.
This type of modulation is based on a pivot chord that is diatonic to both keys, a common chord with no accidentals, that has a different harmonic function in each key. It is used to move between closely related keys. Closely related keys, and their relative major or minor counterparts, have one more or one fewer sharps or flats. They are adjacent on the circle of fifths. Here is an example of the closely related keys to D major:
1# 2# 3#
G D A
e b f#
The diatonic common chord modulation moves to one of the closely related keys by using a pivot chord that immediately precedes the chord with an accidental. The chromatic alteration signals the new key, and becomes part of the new tonality. Common chord modulations often move to the dominant or to the relative major or minor key. Most pivot chords are predominant in function, moving to the dominant chord in the new key which contains an accidental. The accidental is applied continuously to an authentic cadence in the new key.
Unlike the diatonic common chord modulation, a chromatic modulation hinges on a chord with a chromatic alteration. As a general rule, a raised pitch is the leading tone (major 7th) of the new key, and a lowered pitch is the subdominant (4th) of the of the new key. These are good clues to find the tonal center of the key to which the music modulates.
Lacking a common diatonic chord, chromatic modulations often lead to distant keys rather than closely related keys. Typically, a chord that only belongs to the original key is followed by a chord that is diatonic only in the new key. However, altered chords such as a secondary dominant or leading tone chord in the original key can be used as a common chord in a chromatic modulation, as well as borrowed chords. It serves a dual function as a chromatically altered chord in the old key and a diatonic chord in the new key. Other altered chords, such as the Neapolitan or Augmented 6th chords may also be used as pivots. They are discussed in the next lesson.
An enharmonic modulation employs an altered chord that can be interpreted in both the new and the old key, but is spelled enharmonically in either the new or the old key. A leading tone fully diminished 7th chord (viio7) is often spelled correctly by the composer in the new key, serving as a clue to the new tonal center. This chord is a very useful enharmonic pivot chord, given that the same four notes can be spelled different ways to modulate up a half-step from any of the four pitches to a distant major or minor key. Review the example in the Lesson on Secondary Leading Tone Chords for an illustration.
A direct modulation is also known as a phrase modulation because it usually occurs between phrases. The new phrase simply begins and continues in a different key, without the use of a common chord or a common tone. It occurs directly after a cadence in the original key.
A common tone modulation uses a single pitch rather than a chord as a hinge to pivot to change keys. This pitch is typically isolated and repeated, and serves as a different chord member in the harmony of a new key. It may be used in modulating to either closely related or to distant keys, such as a movement to the chromatic mediant key area. A chromatic mediant relationship exists between two chords that are a 3rd apart, and are both major or minor in quality. An example of this is a modulation from the key of E major to G major using the note B as a common tone. Another example is a modulation from G major to the key of B-flat using the note D as a common tone.
A monophonic modulation can be accomplished by a single line as chromatic inflections are introduced that belong to a new key. Harmony can be clearly implied in a monophonic texture as chords are outlined and new scalar material is presented. As accidentals are consistently used moving forward, a new key is established. The use of raised leading tones in the new key is a good clue to the shift in tonal centers. The cello suites by J. S. Bach contain frequent modulations, and movement around the circle of fifths is common in the solo literature. Polyphonic and homophonic textures may contain a short segment consisting of a single line as a transition between two key areas.
A sequential modulation is accomplished by the restatement of a phrase on a new pitch level. Sequences that move up or down by a step are common in tonal music, as are those that move around the circle of fifths. The duration of a modulation may determine whether it is simply a momentary tonicization, or an actual modulation. The context of the sequence in the music and the length of time each sequence lasts are factors for consideration. The melodic sequence is a powerful development technique used by composers in all styles.
Given a score, we can see composers using accidentals consistently and ending phrases with cadences that establish modulations. Without a score, we must rely on hearing the changing tonal centers. The practice of keeping track of the tonic pitch, or “Do” in the music, is a valuable skill to develop. While listening to modulatory music, make note of the timing in the music at the point of modulation, and try to identify the modulatory technique aurally. Then check the score to see if your aural impressions are accurate.