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I've read that in a minor key iim75b can be softened to bVII7 and vii° can be softened to V7. What do I do with a ivm75b? Can it be softened to bII7? Are there cases where this approach results in something that clearly sounds worse?

UPDATE (some context added):

The original chord progression is the following (key of A minor):

Am/E Dm75b/F C/G Dm75b/Ab Em/B Bm75b Am

I see Bm75b can be exchanged with a G7/B, but what about the Dm75b?

UPDATE2: I've added the first half of the melody line.

enter image description here

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    It depends more on which chords are either side of the 'offending' one. Soften doesn't really explain what you want to do - it's subjective anyway. m7b5 is half diminished. – Tim Feb 19 '15 at 14:36
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    I'm not sure what you mean by "softening", but "Dm7b5", or "D half diminished", is not a chord in the key of A minor, since it contains an Ab (this the b5). So the chord progression as written isn't logical. – herman Feb 19 '15 at 18:00
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    @herman - I'm not sure what you mean by logical. Not all of the chords need to be from the key for a piece or section to be considered as in a key. – Basstickler Feb 19 '15 at 18:17
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    Welcome @Basstickler, the bass line was inspired by your teachings. – András Hummer Feb 19 '15 at 18:35
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    Glad to be of service! Can you clarify what you mean by soften as well? I assume it basically means that you would like the same function for a chord but have less dissonance, is that accurate? – Basstickler Feb 19 '15 at 20:10
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The nature of any diminished chord is going to be harsh as just the natural spelling of the chord outlines the tritone used in it. Simple voice leading and making sure the tritone does not show up in the outer voices. This is why it is rather typical to see a diminished chord in an inversion

As to why going from iim75b to bVII7 and vii° to V7 you have to understand how these chords are related. Dominant 7ths naturally have a diminished chord in them between the 3rd, 5th, and 7th and like I talked about earlier, the tritone is not as exposed as it is in just a diminished chord. For example in the key of C major vii° is B° (spelled B, D, F) and V7 is G7 (spelled G, B, D, F). The iim75b and bVII7 follow the same logic.

For the ivm75b changing it to bII7 will create the same effect as before, but this chord in general would seem out of place in most progressions as with both chords you are altering the tonic so the harshness (dissonance) of it will tend to show though even if voiced well. If that's what you're going for then it will work fine and could even lead to a modulation in the right context. If this is not what you are trying to go for, I suggest rethinking the progression at least for that one chord.

  • I got the iim75b->V7 and vii°->V7 part, and since you and @Holaf wondered I've added the imagined chord progression. For the first half I can draw a sheet music about how I imagine the arrangement, just give me a few hours :) – András Hummer Feb 19 '15 at 15:57
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    @AndrásHummer even with the edits, I'm not really understanding the progression with respect to the tonic as the progression seems to more based around E than A. – Dom Feb 19 '15 at 21:01
  • The melody would eventually land on A, only an octave higher, and the final Am has A in the bass as well. I agree it starts off a bit unstable, more like as if it were a C6/E followed by an Fm/D. – András Hummer Feb 19 '15 at 21:18
  • Come to think about it, though half-diminished chords tend to have a dominant taste, in the case of the IVth degree they also preserve their subdominant role, so for Dm75b an Fm borrowed from the C minor key sounds like a reasonable approach for softening. – András Hummer Feb 20 '15 at 13:26
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Such softenings typically require an underlying key that enable to replace a chord by an other one that has common notes, but that makes you stay into the key. The softenings iim75b -> bVII7 and vii° -> V7 presuppose an underlying minor key in which these chords are included. However, ivm75b chords don't imply a key as clearly. It might then be necessary to have more context (surrounding chords, melody, etc.) to soften such a chord by an other.

Edit : thanks for the chord sequence. I am not sure if there are some well defined rules for this kind of cases, and you might then have to count more on your personal aesthetic criteria. That said, I would say that your first softening (Bm75b -> G7/B) would fit with the idea of privileging the A natural minor key rather than A harmonic minor (because it removes the G#). Staying on this direction, you might want to soften your Dm75b in a Dm7.

  • After some time thinking I realized that a iim75b (in the key of A minor, a Bm75b) can also be interpreted as a Dm6/B. In this approach for the Dm75b I can't use Bb7/D for the softening (as its root note is not part of the A minor key), but I can borrow an Fm from the C minor key, making it an Fm6/D chord. – András Hummer Feb 20 '15 at 15:36
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The second chord is not D half diminished as there's no C in the score at that point. However there's a B there, so this is F dim, which is an inversion of B dim. So this is a dominant function to C (normally the F in the bass would resolve down to an E), which means it can be replaced by G7. The Ab in the melody automatically makes it a G7b9.

  • So you say it could be replaced with a G9b/F? – András Hummer Feb 21 '15 at 23:12
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    Sure, if you wish to keep the F in the bass it would be, in proper notation, G7b9/F. (I notice you often put the b behind the number, it's normally in front like b9 or b5, pronounced as "flat nine" or "flat five") – herman Feb 21 '15 at 23:22
  • Note that the 2nd Dm7b5 is different. I think it's also not really Dm7b5 in the first place. Thinking in Am, the bass note makes more sense when interpreted as G# instead of Ab. Then it's just G# diminished, having a dominant function and being almost the same as E7b9/G#. Only the Em/B after that is a bit "weird": going from a dominant function to V minor. – herman Feb 21 '15 at 23:32
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So among the alterations that diminished chords go under, let's assume that your "softening" means to lower the seventh of the chord diatonically to create a dominant seventh chord. This fits all three of your example cases. In Am:

diminished chord | diminished spelling | softened chord | softened spelling
 iim7b5          |  B, D, F, A         |  bVII7         |  B, D, F, G
 vii°7           |  G#, B, D, F        |  V7            |  G, B, D, E
 ivm7b5          |  D, F, Ab, C        |  bII7          |  D, F, Ab, Bb

So let's look at other fully diminished chords. Note that there are really only three of them and most of these are enharmonic spellings to fit our definition of softening. I've tried to keep the sharps an flats as non-ridiculous as possible and general chosen to spell the diminished chords in a way that the softened chord has a more useful function if any function at all.

diminished chord | diminished spelling | softened chord | softening spelling
 im°7            |  A, C, Eb, Gb       |  bVI7          |  A, C, Eb, F
 biii°7          |  B#, D#, F#, A      |  VII7          |  G#, B#, D#, F#,
 #iv°7           |  D#, F#, A, C       |  II7           |  D#, F#, A, B
 vi°7            |  F#, A, C, Eb       |  IV7           |  F#, A, C, D
----------------------------------------------------------------------------
 #i°7            |  A#, C#, E, G       |  VI7           |  A#, C#, E, F#
 iii°7           |  C#, E, G, Bb       |  I7            |  C#, E, G, A
 v°7             |  E, G, Bb, Dd       |  bIII7         |  E, G, Bb, C
 bvii°7          |  G, Bb, Db, Fb      |  bV7           |  G, Bb, Db, Eb
----------------------------------------------------------------------------
 ii°7            |  B, D, F, Ab        |  bVII7         |  B, D, F, G
 iv°7            |  D, F, Ab, Cb       |  bII7          |  D, F, Ab, Bb
 #v°7            |  E#, G#, B, D       |  III7          |  E#, G#, B, C#
 vii°7           |  G#, B, D, F        |  V7            |  G#, B, D, E

You could do a much more in depth analysis of these chords and what scales they're associated with, but right off hand, I notice a few things. First, all of your examples are form the third group. This is to be expected as it is the most function of the three chords and is usually a dominant function. The bVII7 is in the scale, the bII7 could be considered a Neapolitan 6th chord (I'm not sure if dominant seventh disqualifies it), the III7 modulates to the relative minor if we're in a major key, and the V7 speaks for itself. As for the other chords, all of them have the obvious function of modulating to related keys. bIII7, I7, and II7 look good for that. As for functional chords within the key, I like bVI7 as an augmented sixth chord and the II7 and the IV7 look good for some modal flavor. Honestly, it may take some oddness or trickery to get these diminished chords in a progression in the first place and there definitely chords on here that sound odd, but most of the common functional diminished chords (ie the third group) can be resolved in interesting ways. Also for reference, here is the same chart with half diminished instead of whole diminished chords.

diminished chord | diminished spelling | softened chord | softening spelling
 im7b5           |  A, C, Eb, G        |  bVI7          |  A, C, Eb, F
 biii7b5         |  B#, D#, F#, A#     |  VII7          |  G#, B#, D#, F#,
 #iv7b5          |  D#, F#, A, C#      |  II7           |  D#, F#, A, B
 vi7b5           |  F#, A, C, E        |  IV7           |  F#, A, C, D
----------------------------------------------------------------------------
 #i7b5           |  A#, C#, E, G#      |  VI7           |  A#, C#, E, F#
 iii7b5          |  C#, E, G, B        |  I7            |  C#, E, G, A
 v7b5            |  E, G, Bb, D        |  bIII7         |  E, G, Bb, C
 bvii7b5         |  G, Bb, Db, F       |  bV7           |  G, Bb, Db, Eb
----------------------------------------------------------------------------
 ii7b5           |  B, D, F, A         |  bVII7         |  B, D, F, G
 iv7b5           |  D, F, Ab, C        |  bII7          |  D, F, Ab, Bb
 #v7b5           |  E#, G#, B, D#      |  III7          |  E#, G#, B, C#
 vii7b5          |  G#, B, D, F#       |  V7            |  G#, B, D, E

In general, if you're not using one of the diminished chords from the third group, the dominant function diminished chords, softening is going to be odd. But it could be very useful for modulation. Hope this gives some food for thought and I hope I didn't make too many mistakes in my charts.

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