TonalityGUIDE - basic tonal music theory and analysis for undergraduates
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Key and Modulation

introduction major and minor the circle of fifths ways of modulating spotting modulations

relative | parallel

The following two examples contain a very simple modulation: an imperfect cadence in one key followed by a perfect cadence in another. If you listen to the examples you will probably feel that the modulation from C major to A minor in Passage A is quite smooth, but the modulation from A major to Ab major in Passage B is like a sudden jolt.

Not sure about the chord labels? Check out the chord identification section of the Toolkit by following the link at the bottom of this page.

The reason why the modulation in Passage A is so much smoother is that A minor and C major share all the same notes except one (G#). By contrast, A major and A flat major do not have any notes in common:

The harmonic scale of A minor shares all but one note with the scale of C major, as can be seen in the above example (the natural minor shares all the same notes, see minor scales for more about different types of minor scale). Because these two keys are so closely related (and it is therefore easy to modulate from one to the other) A minor is therefore said to be the relative minor of C major. The relative minor of any major key is a minor third below, as shown in the following table.

Relative major and minor

The close relationship between A minor and C major is highlighted if you imagine changing the G# (sharpened leading note of A minor) in the second bar to a G natural. The third chord of the example would then be an E minor rather than an E major chord, and the second bar would sound like ii - vi in C major instead of V-i in A minor.

If you are analysing a piece of music and it seems to have changed key, the relative minor or major is one of the first keys you should check for. As well as a perfect cadence in the new key, you should look out for the following:
  • if the piece has modulated from relative major to minor, the fifth degree of the major scale will have been sharpened to become the leading note of the relative minor
  • if the piece has modulated from relative minor to major, the leading note of the minor scale will have been naturalised or flattened to become the fifth degree of the relative major

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