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I wanted to know if 7th, 9th, 11th and 13th chords can have both augmented and diminished forms. I'd appreciate your answers.

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    Is this a duplicate of music.stackexchange.com/questions/27402/… Dec 28 '21 at 16:01
  • @BrianTHOMAS - The two questions look deeply related but not duplicates to me - the question you bring up is for diminished chords only, while this question is also for augmented chords.
    – Dekkadeci
    Dec 29 '21 at 14:55
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The note augmented or diminished in these chords is ^5. So C7+ will be spelt C E G♯ B♭. Cm7♭5 will be C E♭ G♭ B♭ - often referred to as C half-diminished.

The same works for 9ths, but it's confusing as the 9th part itself can be seen as diminished - as C7 with D♭ added, or augmented - as C7 with D♯ added (as in the 'Hendrix' chord).

Written names will help - C+7(♭9) or C9(♭5) make the actual chord very clear. And, of course, frequently, notes are omitted from 11th and 13th chords, which helps the sound blend, but not the naming...

So keeping any basic 7th, 9th, 11th or 13th chord with either an augmented or diminished 5th replacing P5 is permissable. In fact, any combination of notes will constitute a chord - just need to work out its function and note names to give it a title! But let's face it, some combinations don't sound good everywhere.

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  • Wouldn't an augmented 7th chord have a major seventh?
    – phoog
    Dec 28 '21 at 17:32
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    @phoog - why do you think that? It's not the 7th part that's augmented.
    – Tim
    Dec 28 '21 at 17:51
  • So there's not a diminished third between the chord's fifth and seventh. In a diminished seventh chord, both the fifth and the seventh are diminished. How do we know that a diminished triad has a minor third rather than a major third, and an augmented triad the opposite? It just makes more sense.
    – phoog
    Dec 28 '21 at 18:09
  • @phoog - a dim 3rd is a semitone lower than m3, a tone lower than M3. A dim triad, by definition, contains m3, not M3 or D3.
    – Tim
    Dec 28 '21 at 18:30
  • Right, but why is that the definition? And why would it make sense for an augmented seventh chord to have a minor seventh instead of a major seventh? There are many authorities confirming the definition of the diminished triad. Can you cite one that agrees with your definition for the augmented seventh chord? Where did you get it from?
    – phoog
    Dec 28 '21 at 19:55
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Yes, of course you can put any notes you like in a chord, so the question is more about naming convention.

Typically words augumented and diminished are used for triads only (at least in jazz/pop nomenclature). An exception is a fully diminished chord or diminished seventh chord 1 b3 b5 bb7, e.g. Eo7 (E G Bb Db).

Extended chords still can have diminished/lowered/flat or augmented/raised/sharp fifth, e.g.

  • Em7b5 (E G Bb D) is minor-seventh chord with flat five, often called half-diminished
  • E7#5 (E G# B# D) is dominant seventh chord with raised/sharp fifth
  • E7b5 (E G# Bb D) is dominant seventh chord with flat fifth
  • Emaj7#5 (E G# B# D#) is major seventh chord with sharp fifth

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