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I've been playing with diminished chords as 'V' in ii-V-I progressions. I often use one of the three diminished chords in a ii-V-I progression -- I sharpen the 5th note of the scale and hang a diminished triad over it. So in C major I would use G# diminished for V which is really a rootless G9 so I can understand its dominant function.

But I've just been trying Eb diminished and it sounds dominant too but I don't understand why. (I've been playing 'Almost like being in love', and Eb diminished sounds great over 'being'). I then tried the only remaining diminished chord and it too seems to provide an adequate 'V' function, although it's not as nice as the other two in this context.

So, I'm wondering. Can you use any diminished chord as 'V' anywhere and get away with it, and is my use of Eb diminished over 'being' (i.e. V) a standard substitution? And how does it work?

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    @AmericanLuke The fifth scale degree is diminished in Locrian mode; the V triad is diminished in Phrygian mode. May 28, 2014 at 23:22

7 Answers 7

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I'm not sure whether you're describing full diminished seventh chords (eg. A C Eb Gb) or diminished triads (eg. A C Eb), but both are very closely related to dominant seventh (V7) chords (eg. F A C Eb, dominant seventh in Bb Major).

A diminished triad is the same as a dominant seventh chord without its root. As a diminished seventh chord is symmetrical, consisting of notes that are all three semitones apart, it can be converted to four different dominant seventh chords by dropping any of its notes by a semitone. For instance, the diminished seventh A C Eb Gb can become Ab7 by dropping the A a semitone, B7 by dropping the C, D7 by dropping the Eb and F7 by dropping the Gb. Also, a full diminished seventh chord is the same as any of four 7b9 chords without a root.

It should be pointed out that changes of enharmonic spelling are often necessary to create the correct theoretical type of V7 chord from diminished seventh chords.

An Eb diminished seventh chord would seem to function more like a secondary dominant in C Major (like a D7b9). This should feel like it wants to pull towards the dominant, G, but this "double" pull, towards the tonic from the dominant of the dominant may still make it work okay as a dominant substitution, simply because your ear feels the true dominant and then tonic that you "want" to go to. I bet it would sound even better with a really cheeky little G7 chord after it though...!

Finally, another reason this Eb diminished chord may work well as a strong approach to the tonic triad, is because the Eb (or D#) and the Gb (or F#) want to move upwards by semitone, almost like leading notes, to the third and fifth of the tonic triad. And, the other diminished seventh triad (that isn't on Eb, or on D, the equivalent of the dominant seventh) is on E. This has Db which will "pull" downwards towards the tonic, C.

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Since you're referring to there being only three diminished chords, I'm going to assume you mean diminished seventh chords. In that case, what you're calling a G#dim, I would actually call a Bdim7, and spell (B D F Ab). This has the benefit of making the chord root be a scale degree (the seventh scale degree of the major scale supports a diminished chord). The Ab also makes it a bit clearer that it functions as a rootless G7(b9) chord, as you point out. If you were to spell it as (G# B D F), I'd expect a resolution to some form of A chord.

In general, the root of a dim7 chord can be treated as the major third of a rootless dominant 9th. That makes it the leading tone of some scale, and it wants to resolve a half-step up. From your question, I think you understand this point already. However, because the chord is symmetrical, any of the four tones could be viewed as its root, which gives four possible resolutions. I like to think of it like a "revolving door" of tonality.

But your real question is about what you're calling Eb dim (which would be spelled Eb, Gb, Bbb, Dbb). I'd probably consider this either an F#dim7 (F#, A, C, Eb) or an Adim7 (A, C, Eb, Gb) depending on context. I'm not familiar with the song you mentioned, and I'm not at a keyboard at the moment, so I'm having a hard time seeing how this could substitute for a dominant. However, it looks like it would make a great predominant substitution. I'll edit this answer when I get a chance to try it. So I guess I haven't answered your question yet.

I'm not sure about the third dim7 chord either, but since it includes a bII scale degree, maybe it acts like a modified tritone substitution? I'll have to check that out later as well.

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    +1 for explaining the Bdim7 leading tone diminished seventh chord. But the Eb diminished seventh chord should probably be Cdim7 and called a common tone diminished seventh chord. Or just call it a passing diminished seventh between ii and I. Feb 26, 2019 at 19:55
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A fully diminished chord is a V7b9 voicing. So wherever is appropriate to use a V7b9 the diminished chord is already a part of it.

In general, a diminished chord has a dominant function because it contains the tritone. A fully diminished chord contains two pairs of tritones, which means it can be used to resolve to four different target chords. For example, a fully diminished Bdim7 contains:

b and f

d and Ab

The tritone "b" and "f" can resolve to a C chord or a Gb chord. The tritone "d" and "Ab" can resolve to a Eb chord or a A chord.

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Personally, I think there is only one real third and one flat seven - the tritone - in a "Dominant" form chord. Such a chord has to be considered as "being" somewhere, i.e. it has Function in whatever sequence may be. Flat 9s and dim chords are the same thing : You have to consider, for practical purposes, which tritone You choose to identify as the "name" of the so-called diminished chord. In short, so-called diminished chords are Dominant form chords - whatever they have as scales : flat 6, natural 6, sharp 4, no 4 - they must still retain their fundamental 3 and flat 7. In the end, Friends, "diminished" chords are just plain old Dominants, 3 - flat 7, with the scales "altered".

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No, you cannot use any diminished 7th chord as a dominant-function chord and get away with it.

Any diminished 7th chord that does not include the home key's leading tone and is immediately followed by a tonic chord is a common-tone diminished 7th chord instead. This is called that because it shares at least one chord tone with a neighbouring chord. Common practice period harmony will let you switch back and forth between the tonic chord and its common-tone diminished 7th chords freely, but don't mistake that for a dominant function.

We can extrapolate this C major example for all major keys - just transpose accordingly.

  • Tonic chord: C major
  • B-D-F-A♭ and enharmonic chords: Dominant-function diminished 7th (leading tone is B)
  • F♯-A-C-E♭ and enharmonic chords: Common-tone diminished 7th (shares C)
  • C♯-E-G-B♭ and enharmonic chords: Common-tone diminished 7th (shares E and G)

There are only 3 diminished 7th chords possible if we assume all enharmonic notes map to one of their corresponding notes each, so we are done.

This is the equivalent, C minor example for minor keys:

  • Tonic chord: C minor
  • B-D-F-A♭ and enharmonic chords: Dominant-function diminished 7th (leading tone is B)
  • F♯-A-C-E♭ and enharmonic chords: Common-tone diminished 7th (shares C and E♭)
  • C♯-E-G-B♭ and enharmonic chords: Common-tone diminished 7th (shares G)
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  • Hm. I've heard of the leading-tone diminished 7th (in C, Bdim7), as well as the common-tone diminished 7th (Cdim7). But I've never really heard C#dim7 to C called a C.T. dim 7th, despite how logical the name sounds. The way I usually look at it, the "common tone" is the root of the chord it resolves to, so the root doesn't change - that's what's being held common in the resolution. For C#dim7 to C, I would deem that an upper leading-tone diminished 7th, like how the Em7 Ebdim7 Dm7 G7 progression works. But that's just name-calling, doesn't matter as long as we all understand the sound!
    – user45266
    Jan 14 at 21:55
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Can any diminished chord be used as V anywhere?

In tonal harmony you can play a diminished chord on any root any time and have it act as a dominant (better to call it a dominant and not a V, it's Roman numeral should always be viio) to some tonic. But that statement is broad to the point of not being useful.

You asked about "anywhere?" What do you mean exactly?

This wording is too vague, we are talking about tonal harmony, we need specifics about key and chord, words that have musical meaning, not pronouns.

The matter is entire about the sense of being in a key.

Keys have tonics of either a major or minor triad, those tonics have leading tones, and a diminished chord can be built on the leading tone which has a dominant function resolving to the tonic chord. Those concepts are all bundled up when symbols like I, i, or viio are used.

You can change key or temporarily tonicize another tonic in tonal music.

A secondary leading tone chord, the viio chord, can be applied to any diatonic chord, except the viio chord, or iio chord in minor, because a diminished chord cannot be a tonic in tonal harmony.

So, for example, in C major you can have viio itself and secondary chords viio/ii, viio/iii', viio/IV', viio/V', viio/vi'. But, you cannot have viio/viio. In C major that would be a Bb diminished chord claiming to resolve to a tonic of B diminished, which is tonal nonsense.

However, you could have music in C major, introduce a Bb diminished chord, and it would imply a change in the tonal focus, that chord would resolve to either a B major or B minor tonic. It would really take you away from C major.

This brings us back to what you mean by "anywhere?"

If you mean, can I use a diminished chord anywhere within a give key, and keep within the conventions of tonal harmony? Then, no.

You posed the question with reference to Roman numeral analysis and function. That frames the question within the conventions of tonal harmony.

If you mean, can I use a diminished chord anywhere, regardless of key or tonal conventions? Then, yes. You can use any chord any time. It just won't necessarily be conventional tonal harmony.


...in a ii-V-I progression -- I sharpen the 5th note of the scale and hang a diminished triad over it. So in C major I would use G# diminished for V...

If the purpose is to use diminished chords as dominants, it will clarify things to think of them with the common label leading tone chords, leading tone triad or leading tone diminished seventh chords.

So, this case will be less confusing if the chord were spelled as a leading tone diminished seventh chord. Not G# B D, but Ab B D which is just an inversion of B D Ab, which is simply the viio7 chord in C major. That makes ii V I become ii viio I, and that functionally the same: subdominant dominant tonic. In other words, if it's functioning as a dominant the root is not G# leading tone to A, but root B leading tone to C.

...I've just been trying Eb diminished and it sounds dominant too but I don't understand why...

The voicing might matter with this one. I played it in close voicing Dm7/C Ebdim7/C Cadd6 (you call it an Eb diminished so I wrote Ebdim7/C instead of Cdim7.) With my particular voicing you have a chromatic ascent of D F, Eb Gb, E♮ G♮. Chromatic steps like that certainly have "pull" but that doesn't sound like dominant function. Dominant function is TI FA resolving to DO MI. So, this case is a kind of embellishing or passing chord, not a dominant. Like @Dekkadeci answer, you can all it a common tone diminished seventh chord.

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4 things:

  1. Barry Harrisy chord right there. Could think of it as resolving to Cmaj6/E spelled (E G A C). Sounds very nice when approached with a Ddim7.

  2. That Ebdim is a #superhip way to spell a g chord that gives jarring bright results

  3. As suspension rather than dominant, because Ebdim7 spelled (Eb Gb/F# A C) is like just a C6sus where the 5th and 3rd are Sussed out. It will feel the same as the bVdim or i dim. It also goes beautifully to a two chord, so using it as the 1 is a really nice way to delay release enjoy.

  4. Tension goes home. It doesn’t really matter where, with nice voice leading or even just intention, you can make anything go anywhere. It’s a v7 chord if you say it is.

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