In this chapter, the modulation types will be mentioned. They will be explained in more details using examples in the chapters that follow.
There are two basic modulation types: common chord modulation and direct modulation. Common chord modulation happens gradually while direct modulation happens instantly. If a modulation happens gradually, a listener is more prepared for the new key. In this case, one or more chords which can be expressed in both the keys occur around the location of the modulation. These chords are called common chords. If a modulation happens instantly, a listener is surprised by the new key. In this case, there are no common chords.
Common chord modulation can be diatonic or altered. This will be explained in the chapters that follow.
Various other modulation types can be used in combinations with the modulation types described above to further describe the character of the modulation. These are common tone modulation, enharmonic modulation, chromatic mediant modulation and sequential modulation.
A direct modulation where a single pitch belongs to the last chord in the old key and to the first music chord in the new key is called common tone modulation. The pitch can be sustained or repeated across the location of the modulation and is called the common tone. Common tones usually appear in the melody.
In enharmonic modulation, one or more notes are written in the score in one of the keys (the old or new key) but they must be enharmonically respelled so that they can be expressed properly in the other key. When common chord modulation is enharmonic modulation then the common chord belongs to both keys but requires enharmonic respelling in one of them. When common tone modulation is enharmonic modulation, the common tone belongs to both keys but requires enharmonic respelling in one of them.
A modulation in which the new key is a chromatic mediant of the old key is called chromatic mediant modulation. Chromatic mediants were explained in chapter Chromatic mediants.
Sequential modulation is a modulation that is realized by using the harmonic sequence.