Learning Resources: Modulation
Some preliminary notes
Before you look at the examples of modulations on the following pages, you should read the notes below carefully. It is important to understand the basics of how modulations work, or you will not be able to make sense of what Bach is doing.
The easiest way to modulate is to change key at the beginning of a phrase, so that each phrase stays in the same key. This is called a phrase modulation (i.e. the new key starts at the beginning of the phrase). In the example below, the second phrase begins with a phrase modulation - the previous cadence is in E major and then the beginning of the new phrase starts in A major.
There are several circumstances that make staying in the same key for a whole phrase impossible:
- if accidentals (or a lack of accidentals) make the cadence key impossible at the beginning of the phrase
- if the beginning of the phrase cannot be harmonised in a sensible way using the cadence key. For example, if the only possible harmonisation using primary chords is IV
-IV-I this might indicate that you are in the wrong key.
- if the key at the end of the previous phrase is too distant from the cadence key of the next phrase (i.e. not adjacent on the closely related keys diagram)
The alternative to phrase modulation is to modulate using a pivot chord – a chord in the middle of the phrase that makes sense in both keys allowing you to move smoothly from one to the other. In the example above, the first phrase uses a pivot chord to get from A major to E major. The A major pivot chord (marked with a red box) functions as chord I in A major (the old key) and chord IV in E major (the new key).
Note the chord labelling: the new key starts on the line below overlapping by one chord (the pivot) with the old key.
Pivot modulation method
- Work through the phrase until you come to a melody note that can only be in the new key (i.e. it is not part of the scale in the old key)
- The chord before that identified in step 1 will be your pivot chord
- See what chords in the NEW key can fit with your pivot chord – ideally it should be on of the following:
- V (best followed by I or IV)
- IV (best followed by V or I)
- ii (must be followed by V)
- vi (best followed by IV, ii or V)
- Now check that the pivot chord makes sense in the old key and does not make a bad progression with the previous chord (see harmonic DOs and DON’Ts)
- To modulate, the safest option is to use primary chord pivots where possible.
- To modulate between relative major and minor keys, try using vi in the major / I in the minor as the pivot
Analyze the examples on the following pages in order to learn about how Bach modulates between different keys. Remember to use the relevant pages of the logbook to guide your explorations.
Some extra notes
On the whole it is safest to use primary chords as pivot chords (you can work out modulations in step 2 of the method). This does not work, however, when pivoting between relative major and minor - have a look at the examples on the following page to find how Bach modulates between these two keys.
Bach will sometimes modulate more than once in a chorale. The elegance of Bach's harmonisations often come from these modulations in the middle of the phrase. It is safer, however, for students to modulate only when absolutely necessary, so you should avoid this unless you have looked at lots of examples and really feel like you know what you are doing.
There is one other type of modulation, that is best avoided in chorale exercises - the abrupt modulation. In this type, the chord progression V - I is used to jump straight into a new key without sharing a common chord with the old key.