Modulation is the action of moving from one key or tonal center to another. Modulations can be between closely related keys (keys separated by at most one sharp or flat in their respective key signatures), or between distantly related keys (keys separated by more than one sharp of flat in their respective key signatures). Modulation to foreign keys occurs somewhat frequently in romantic music and certain 20th century musical styles. Modulations can also be quite brief, and some musicians may hear these as tonicizations rather than modulations. As with many things in music, modulations are at times open to interpretation and the dictates of individual musical taste.
Before we examine the diverse types of modulation, we should delve into the various key relationships. These can be summarized as follows:
- Relative – A major mode key and a minor mode key that have in common the same key signature are called relative keys. An example of this is C major and a minor. Relative keys are also closely related.
- Enharmonically Equivalent – Two keys that are both major mode or both minor mode that sound the same but are spelled differently are called enharmonically equivalent keys. Examples of these are C♯ major and D♭ major, and g♯ minor and a♭ minor. Moving between these is not considered modulation because the tonic notes are enharmonic.
- Parallel – A major mode key and a minor mode key with the same tonic are called parallel keys. For example, the keys E♭ major and e♭ minor. Changing from E♭ major to e♭ minor is considered a change of mode (a.k.a. mode mixture), and not a change of key because the tonic note does not change.
- Closely Related – Two keys that are separated by no more than one sharp or flat in their respective key signatures are called closely related keys. It could be two major keys such as C major and F major, two minor keys such as d minor and g minor, or a major and minor key such as D major and e minor.
- Foreign or distantly related – Two keys that are separated by more than one sharp or flat in their respective key signatures are called foreign keys. Examples include C major and D major, F major and F♯ major, and C major and a♭ minor. Modulations to remote, distantly related keys are more typical of the Romantic era than of earlier music.
Finding Closely Related Keys
To find the closely related keys to any given key, it is simple enough to think of the major and minor keys that are separated by no more than one sharp or flat in their respective key signatures. You can also use the following chart to find closely related keys.
Tonic key Subdominant key Dominant key
Relative major/minor Relative major/minor Relative major/minor
To identify the keys closely related to C major, we would fill out the chart in this manner:
C F G
a d e
To identify the keys closely related to b minor, we would fill out the chart in this manner:
b e (minor subdominant) f♯ (minor dominant)
D G A
The most common modulations are between closely related keys. In major keys the most common modulation is from the tonic key to the dominant key, and in minor keys the most common modulations are from tonic to the mediant key (the relative major) or to the minor dominant key.
Before covering the types of modulation, the concept of common chords must be discussed. Common chords are chords that are shared by two keys. Keys that are closely related will share several chords in common, while keys that are distantly related will share few or no chords in common. In the following example, the chords shared by C major and its dominant G major are identified.
- The C major triad is a I chord in the key C and a IV chord in the key of G.
- The E minor triad is a iii chord in the key of C and a vi chord in the key of G.
- The G major triad is a V chord in the key of C and a I chord in the key of G.
- The A minor triad is a vi chord in the key of C and a ii chord in the key of G.
Types of modulation:
Common chord or pivot chord modulation (modulation typically occurring within a phrase)
Common chord modulations feature a common chord that serves as a pivot connecting two tonalities. The common chord (pivot chord) is usually a diatonic chord in both keys but is sometimes a secondary function in one or both keys. The common chord is often the ii or IV chord in the new key, which allows for quick tonicization of the new key. This chord often precedes the first dominant function chord in the new key, including cadential six-four chords. The new key is often confirmed by an authentic cadence shortly after the modulation occurs. It is possible for there to be more than one pivot chord, which creates a “grey area” in which one key smoothly transitions to another. The best way to identify the presence of a common chord is to find the first chord that makes little sense in the old key and go back one chord. If a common chord is present, it will usually be that chord.
Mode mixture can be used to increase the palette of possible keys and chords, which simplifies modulation to some foreign keys. The following example is the same as that above, but now the modulation is to the remote key of g minor rather than the closely related key of G major. We will examine mode mixture in more detail in a future chapter.
Chromatic modulation (within a phrase)
Chromatic modulation, also called modulation by chromatic inflection, is initiated by the chromatic shift of one or occasionally two pitches at the point of modulation. Chromatic modulation can be used to modulate to foreign keys, including those in a chromatic mediant relationship, as shown in the following example.
Sequential modulation (modulatory sequence) (within or between phrases)
Sequential modulation is achieved using a melodic and/or harmonic sequence in which a passage of music is simply stated in a new key, thus tonicizing a new pitch. Sequential modulations can involve as few as two chords or can be as long as an entire phrase. These modulations often follow the circle of fifths and may involve the use of secondary dominants. The following example is taken from measures 8-10 of the third movement of Mozart’s Piano Sonata in D major, K. 284. The theme modulates via a common chord modulation to the dominant in measure 5, and then returns to the tonic key in the third phrase via a sequential modulation.
Phrase or Sectional modulation (between phrases or sections)
In a phrase modulation, a new phrase or section simply begins in a new key. Phrase modulations can involve common chords, and the typical practice is for the cadential chord of the first phrase to be the common chord with the new key. This can be viewed as a phrase modulation that is “smoothed over” with the presence of a common chord. Phrase remodulations to the tonic are a common occurrence at the beginning of the second part in forms such as binary, rounded binary, and incipient ternary. Some musicians refer to phrase modulations as “direct modulations,” while other theorists reserve the term “direct modulation” for a modulation that occurs within a phrase that does not clearly fall into any other category of modulation.
Common-tone (pivot-tone) modulation (within or between phrases)
Common-tone modulations can serve to bridge keys that are closely related or that are foreign, including those that stand in a chromatic mediant relationship. Common tone modulations typically feature a single tone that is common to two keys that is used as the pivot. These modulations can be quite dramatic in sound. The common tone is often highlighted by thinning the musical texture, thus making it a bridge or connection to the next key.
Chromatic mediants are chords with roots a m3 or M3 apart, share one common tone, and that are both major triads or both minor triads. In seventh chords, the triads are both major or both minor. This is different from the diatonic mediant relationship, wherein the chord roots are a third apart within a given key.
The following example illustrates a common tone modulation between keys that are in a chromatic mediant relationship.
Enharmonic modulation (typically within a phrase)
In an enharmonic modulation the common chord is reinterpreted enharmonically allowing it to function in the second key. The two types of chords used in enharmonic modulations are the Mm7, which can be interpreted as a dominant seventh (V7) and as a Ger+6 chord, and o7 chords, which have a large palette of keys to which they can progress. We will return to the topic of enharmonic modulation in the chapter titled Augmented Sixth Chords and Enharmonic Modulation.