Altered chords

Altered chords are a special category of chords that, as the name implies, alter other chords. There are, for example, altered dominant seventh chords with a flattened or a sharp fifth: 7-5 and 7+5.

See diagrams of altered chords:

Theory

Theory of this chord category is presented here.

We can compare a normal dominant seventh chord with altered dominant chords in the note of C:

C7: C – E – G – Bb
C7-5 (C7b5): C – E – Gb – Bb
C7+5 (C7#5): C – E – G# – Bb

Instead of minus (-), flat (b) is sometimes used and instead of plus (+), sharp (#) is sometime used. Therefore, C7-5 and C7b5 is the same chord and C7+5 and C7#5 is the same chord. Note also that C7+5 contains the same notes as Caug7.

Comparing a normal dominant seventh chord with another pair of altered chords.

C7: C – E – G – Bb
C7-9 (C7b9): C – E – G – Bb – Db
C7+9 (C7#9): C – E – G – Bb – D#

The names of these chords are C dominant seventh, sharp ninth and C dominant seventh, flat ninth. C7-9 and C7+9 can also be written C7b9 and C7#9 respectively.

Comparing with a third group of altered seventh chords.

C7: C – E – G – Bb
C7+11 (C7#11): C – E – G – Bb – F#

The name of this chord is C dominant seventh, sharp eleventh (a correspondent C dominant seventh, eleventh flat ninth does not exist). C7+11 can also be written C7#11.

Other altered chords

Finally, some less common categories.

Altered ninth and thirteenth chords.

C9#11: C – E – G – Bb – D – F#
C13b9: C – E – G – Bb – Db – F – A
C13#11: C – E – G – Bb – D – F# – A

C9#11, C13b9 and C13#11 can also be written C9+11, C13-9 and C13+11 respectively.

Chord categories