Diminished (dim, °, dim7, °7) and Half Diminished (m7b5, -7b5, )

Big difference in usage

The half diminished chord (m7b5) is a diatonic chord of the major scale. It stands on the 7th scale degree*. That means a Bm7b5 e.g. can be used in a song in C major (respectively A minor).

*) which is the 2nd scale degree in parallel minor.

The diminished chord (dim7, °7) is not part of the major or minor scale.

Examples

Half diminished (m7b5)

One of the most common progressions for the m7b5 chord is the 2-5-1 progression in minor vor. Here is an example in A minor (parallel minor of C major). Bm7b5 is the diatonic chord on the 7th scale degree of C major, hence it's on the 2nd scale degree of the parallel minor key A.

E7 is the 5th scale degree of A minor and resolves to the 1st degree Am (that's why we can change Em7 to E7 here).

Diminished (°7)

The diminished chord often acts as a transition chord between the scale degrees of the major/minor scale.

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