Diminished / half diminished

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brojanglesbrojangles Frets: 362
edited February 2022 in Theory
How come some people tell me the ii chord in a minor key progression is a diminished chord, and others that it's a minor 7 flat 5 / half-diminished chord? And who's right? 
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  • It’s a Diminished Chord if you are just using the Root, flat 3rd, and flat 5th notes. If you add the 7th, which is a flat 7th, then it becomes a Minor 7 flat 5 (half diminished chord). For reference, a full Diminished 7th Chord has a flat 3rd, flat 5th, and double flatted 7th.
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  • TanninTannin Frets: 5268
    It is a half-diminished chord. (Mostly.) It is also the 7th degree of a major key.  

    A full diminished chord is not possible within the bounds of a normal major or minor key (that doesn't mean you don't play one, of course, simply that it is not diatonic, so treat with appropriate care). Full diminished chords are diatonic in harmonic minor and any of the related modes (e.g., dominant phrygian).

    A half-diminished chord becomes a minor7 flat 5 under two circumstances:

    (a) If you are playing jazz or hanging out with jazz players. (Why? Ask a jazz player if you have an hour or two spare.)

    (b) When you are resolving it in the "wrong" direction. From memory, diminished chords theoretically resolve up, e.g., B half-diminished ==> C. If you resolve it downwards, it is a minor 7 flat 5.

    WARNING: this last part from memory and I'm vague on it. I learned this a few months ago from an excellent video, but have forgotten already. See: 



    Time I watched it again myself.
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  • If you're just looking at root + third + fifth, it's 1 b3 b5...there's not enough information to discriminate (although the musical context could provide that).

    Once you add the seventh:
    • a 'half diminished' chord is 1 b3 b5 b7
    • a diminished chord is 1 b3 b5 bb7
    So your ii chord is the m7b5 (a bb7 wouldn't be diatonic).
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  • For further amusement...check this out:
    • play an ascending sequence of diatonic 7th chords, e.g. Cmaj7 Dm7 Em7 Fmaj7 G7 Am7 Bm7b5
    • play the same sequence again but, every time there's a gap between root notes, fill it with a diminished 7th chord, e.g. Cmaj7 C#dim7 Dm7 D#dim7 etc.

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  • TanninTannin Frets: 5268
    ^ I see what you did there. :)
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  • Having looked at the video in @Tannin comment above, I do note that even the guy doing the video admits his views are controversial, and personally I find the views expressed somewhat artificially rigid......... but then I like jazz.  ;)
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  • robertyroberty Frets: 10893
    My brain hurts
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  • Tannin said:

    (a) If you are playing jazz or hanging out with jazz players. (Why? Ask a jazz player if you have an hour or two spare.)

    [starts stopwatch]
    it's cos we can spell
    [stops stopwatch]
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  • kelpbedskelpbeds Frets: 180
    edited February 2022
    More amusement, play m7b5 arpeggios from the major third of a dominant 7th chord to create a dominant 9 sound. Great in a Blues context. 
    Check out my Blues lessons channel at:  https://www.youtube.com/channel/UCBTSHf5NqVQDz0LzW2PC1Lw
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  • tanihhiavlttanihhiavlt Frets: 659
    edited February 2022
    play a diminished chord and move ANY note  a semitone lower - that note is now the root note of the resultant dominant chord. Move ANY note up a semitone from a diminished chord and it's a m7b5 (the moved note is the 7th - so a tone up is the root ;^) 

    Dim and Aug chords - really useful :)
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  • ArchtopDaveArchtopDave Frets: 1367
    edited February 2022
    My main coffee mug has an ABC of Musical Definitions on it. Love that fact that J is "Jazz. Originally a four-letter word. Still a four-letter word" .
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  • Thanks for the wisdom, everyone. Also, lol @digitalkettle's pic.
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  • kelpbeds said:
    More amusement, play m7b5 arpeggios from the major third of a dominant 7th chord to create a dominant 9 sound. Great in a Blues context. 

    I was just going to ask about how to use it. I've just been learning about m7b5 chords, and after some messing around noticed that they were spelt the same as dominant 9 chords.  So the question is when it sounds right, how do you know over any given chord, whther you're playing a m7b5 or a dominant 9th chord?
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  • kelpbeds said:
    More amusement, play m7b5 arpeggios from the major third of a dominant 7th chord to create a dominant 9 sound. Great in a Blues context. 

    I was just going to ask about how to use it. I've just been learning about m7b5 chords, and after some messing around noticed that they were spelt the same as dominant 9 chords.  So the question is when it sounds right, how do you know over any given chord, whther you're playing a m7b5 or a dominant 9th chord?
    It depends on the harmonic context in which you are playing the chord. In terms of actually playing, you're making sound(s), so that's ultimately what's important. What you call the sound(s), that you are playing, can be much debated from a theoretical point of view, and may cause brain pain..... but then that's part of the masochistic pleasure of being more jazzy. :)
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  • True, I am in the phase of trying to name what I'm playing to give it some logic, at least to myself.  I'm trying to bust out of the good old pentatonic shapes, and just playing any notes within a given scale, just because it'll fit in the key. It does have the effect of brain melt sometimes.
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  • RolandRoland Frets: 8590
    This is one of those occasions when theory might be useful for naming the notes you play, but shouldn’t determine which notes you play.
    Tree recycler, and guitarist with  https://www.undercoversband.com/.
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  • vizviz Frets: 10643
    ^ That’s all occasions!
    Roland said: Scales are primarily a tool for categorising knowledge, not a rule for what can or cannot be played.
    Supportact said: [my style is] probably more an accumulation of limitations and bad habits than a 'style'.
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  • @digitalkettle "play the same sequence again but, every time there's a gap between root notes, fill it with a diminished 7th chord, e.g. Cmaj7 C#dim7 Dm7 D#dim7 etc."

    I did was and was like, whoah, with this one simple trick, I have become The Ink Spots. 

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  • vizviz Frets: 10643
    @digitalkettle "play the same sequence again but, every time there's a gap between root notes, fill it with a diminished 7th chord, e.g. Cmaj7 C#dim7 Dm7 D#dim7 etc."

    I did was and was like, whoah, with this one simple trick, I have become The Ink Spots. 

    Very similar to doing secondary dominants, but with smoother bass lines
    Roland said: Scales are primarily a tool for categorising knowledge, not a rule for what can or cannot be played.
    Supportact said: [my style is] probably more an accumulation of limitations and bad habits than a 'style'.
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  • @digitalkettle "play the same sequence again but, every time there's a gap between root notes, fill it with a diminished 7th chord, e.g. Cmaj7 C#dim7 Dm7 D#dim7 etc."

    I did was and was like, whoah, with this one simple trick, I have become The Ink Spots. 

    That's the Youtube vid title...just need to film it and wait for the ad revenue to come rolling in!
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