Altered chords
Altered chords, or alterations, means that a note in the chord is altered. For example, a flattened fifth in a C9 chord would result in a C9b5. This can be illustrated in the following comparison:
- C9: C E G Bb D
- C9b5: C E Gb Bb D
Alterations also involve sharpen notes, as in C9#5. Once again can the alteration be illustrated by a comparison:
- C9: C E G Bb D
- C9#5: C E G# Bb D
The following will look closer on some altered chord categories:
Movable altered chords
C7b5
C7#5
C7b9
C7#9
C9b5
C9#5
C13b5
Cm#5
The chord names
The flatted tone is sometimes marked with a minus sign instead of the flat sign: C7-5. They are also often written partly in parenthesis, marking the alternating part of the chord: C7(b5).
The sharpened tone is sometimes marked with a plus sign instead of the flat sign: C7+5.
Theory and progressions
Altered chords are most used in jazz. Notice that these chords tend to be atonal (use notes outside the key). They are often used as passing chords or substitutions. This will be illustrated with two chord progressions:
Using an altered chord as a passing chord can be made by placing it directly before or after its non-altered version and both are often played in in measure:
Bm7 - E7 - E7b9 - Amaj7
Using an altered chord as a substitution can be made by replacing its non-altered version with it:
Bm7 - E7b9 - Amaj7 (instead of Bm7 - E7 - Amaj7)
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