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ChoraleGUIDE: writing four-part harmony in the style of Bach

Method - Step 2a: Planning modulations

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see notes on modulation

Once you have decided on the keys cadences, you need to think about the key for the start of each phrase before you you can go onto the next step of completing a simple primary-chord harmonisation.

The easiest course of action is to start each phrase in the key in which it cadences. Any changes of key can then be handled by using a phrase modulation (the new key starts at the beginning of the phrase). However, there are several circumstances that may stop you being able to modulate in this way:

  • 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)

In such cases, you will need to use a pivot modulation. Modulations are discussed in the next step of the method and there are examples of modulations on the resources pages.

In this example, the first phrase is straightforward as the home key is G major and this is the key of the first cadence. There therefore is no good reason not to start the chorale in G and end the first phrase in this key.

The second phrase, however, is more awkward. It ends in D major, but if you harmonise the beginning in this key using primary chords there are no dominant chords for the first five beats - only I and IV. This indicates the it might be better to start the phrase in G and then move to D later in the phrase. Modulating within a phrase is covered in the next step of the method.

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© Copyright Thomas Pankhurst