CHANGING KEYS
MODULATION
Often composers will create interest and contrast in their pieces by modulating into another key. It is possible to modulate from any key into any other key, but modulations usually work best when you modulate into a closely related key. There are a number of techniques composers commonly use to make their modulations sound 'natural' and satisfying. Here are a few of the most common modulation techniques:
PIVOT CHORDS
The most common way to modulate from one key to another is to use a pivot chord. A pivot chord is usually a chord common to both the key you're in and the key you want to change into. To use this technique, you will need to know your CHORD FAMILIES. Let's say we're in the key of C Major, and we want to change into the key of Bb.
The (Triad) Chords of C are: C, Dm, Em, F, G, Am, Bdim.
The chords of Bb are: Bb, Cm, Dm, Eb, F, Gmin and Adim.
The Chords Dm and F are common to both keys, so we could use either of these chords to 'pivot' from one key to another.
PIVOT CHORDS IN ACTION!
Pivot chords are normally used to modulate to closely related keys, as the two keys in a pivot-chord modulation need to share at least one chord in common.
The diagram below shows which chords the key of C major shares with it's two most closely related keys: G Major and F Major.
Below are some examples of music where pivot chords have been used to modulate from one key to another. Notice that these chords are analysed as being in both keys, and that each of the pivot chords have more than one roman numeral and function.
In the example above, the chords Emin and Amin have been used to pivot from C Major to G Major. This is a fairly straight-forward modulation, as the two keys are closely related.
When pivoting to a key that is less closely related to the original key, composers will sometimes change the quality of the pivot chord to help propel the music forward into the new key. We can see this in the example below, where the C chord has been turned into a dominant chord to help establish the new key-centre of F minor straight away.
Note that in the above example, the chord C7 is labelled V7/IV, rather than I7 (as we would probably identify it in jazz). This isn't a 'slash chord' or a mistake, but rather the result of the way that classical music theorists think about dominant chords. The IV chord in the key of C Major is F major, and C7 is the fifth (or dominant) chord of F. C7 is therefore the 'V of IV' or V/IV.
PIVOT CHORDS: EXERCISES AND WORKSHEETS
FUNCTIONAL (CHROMATIC) MODULATION
The above example can also be thought of as a chromatic or functional modulation. In functional harmony, chords have one of three 'functions': Tonic, sub-dominant or dominant function. The function of a tonic chord is to create a sense of peace or resolution, whereas the function of a dominant chord is to create tension. (Sub-dominant chords are somewhere in between these two extremes, and are typically used to 'set up' the dominant chord). We can make modulations feel 'natural' by introducing the new key through a V-I resolution.
SECONDARY DOMINANT CHORDS
This is commonly achieved by turning one of the secondary chords of the original key into a dominant chord in the new key. These chords are sometimes referred to as secondary dominants. Alternatively, you can 'tonicise' any of the diatonic chords in a scale by playing their related dominant chords.