Diminished Substitutions

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As was observed in the chapter on Harmony, many diminished chords are acting as substitutes for dominant seventh chords. For example, consider the following progression:

[EXAMPLE]

Here, the C#dim7 chord is functioning as a substitute for an A7 chord. The C#dim7 chord is indeed contained within an A7b9 chord:

[EXAMPLE]

Furthermore, the next chord in the progression is Dm, and A7 leads to Dm very well. You can therefore substitute A7 for C#dim7 in this context, and use any scale associated with A7 over the C#dim7 chord:

[EXAMPLE]

However, the C#dim7 chord may be written as Edim7, Gdim7, or Bbdim7, since the diminished seventh chord is symmetric:

[EXAMPLE]

Conversely, in other situations, C#dim7 relates to and may substitute for any of C7, Eb7, or Gb7:

[EXAMPLE]

How then do you know what dominant seventh chord to substitute for a diminished chord, or whether the substitution is appropriate at all?

In general, when you see a diminished chord, you should consider the possibility that it is substituting for a dominant seventh chord. The easiest way to tell is to look at the next chord and determine what dominant seventh chord would normally precede it. If the diminished chord in question shares several notes with the dominant seventh chord that would have been expected, then you can substitute that dominant seventh chord.

For example, consider the following progression:

[EXAMPLE]

Here, the D#dim chord is followed by Em. An Em chord would normally be preceded by its V chord, B7. And indeed, D#dim is related to B7:

[EXAMPLE]

Therefore, B7 makes an appropriate substitute for D#dim in this situation. Now consider the following progression:

[EXAMPLE]

Here, the D#dim is followed by Dm. A Dm chord would normally be preceded by A7. But D#dim and A7 are not related:

[EXAMPLE]

Therefore, A7 is not appropriate as a substitute, and you should simply use the diminished chord as is.

Copyright 2000 Outside Shore Music
Authored by Marc Sabatella

Diminished Substitutions