Thursday, December 15, 2005

Diminished Chords

I've never been sure quite what to make of diminished chords. My jazz teacher, Steve Hillis, contended that diminished chords were almost always substitutions. The blues players would use them because you essentially get 4 chords in one (the dim chord is symmetrical around each of its notes) ... the sub is often for the half dim -- Rmb5b7. In fact in fake books, you often see the dim chords written with the wrong root. I know that the diminished started being used back at the end of the Baroque period (CPE Bach writes about it ... but only the tritone, no bb7) as instruments became louder with more complex harmonics, and as music began to use more colorful harmony, and needed more dark, dissonant chords in their arsenal. But beyond that, never really found an explanation for using them. I think too that you can get away with throwing diminished chords into a minor song, and nobody is the wiser (maybe just me).

So I came across a discussion on TalkBass, and had a couple of very convincing explanations for the role of the dim chord ... it started with a Cdim.

Cdim Chord:
C Eb Gb A

Cdim scale:
C,D,Eb,F,Gb,Ab,A,B (no bbs or ##s for clarity)

In your scale you've left out one of the notes, and it's a chord tone. Just because in triadic harmony you don't play the (double flat) seventh, doesn't mean you leave it out of the scale. What scale would you play over a D- chord in the key of C? D,E,F,G,A,B,D? No, you'd include the C, even though the chord isn't written as D-7. The same applies here.

If you look at old American sheet music, you'll see the chords all over the place, usually for tension/resolution purposes. I'll have to leave the why's to someone else for that. These days you often hear those chords replaced by a II-V, or a related dominant sound. But I understand why Westland's teacher might make such a comment. It's common in some circles to see a progression like this:

|Eb |G-7 C7 |F-7 |A-7 D7 |etc

replaced by this:

|Eb |Eo |F-7 |F#7 |

"half-diminished" or -7b5, is not a substitution for -7 per se, it's a part of minor harmony. You'll usually see it in a "minor II-V," going to V7b9 (not "V9") and on to I- in the key of the moment.

| A-7b5 |D7b9 |G-7 | etc

It's just a different thing altogether.

About half-whole diminished, here's the thing. It's very common for players to play diminished scale-based ideas on dom7th chords. For example, on C7: Eo or Go or Bbo or Dbo. Playing these at the piano will show you that they are all the *same* scale, just starting on a different note. So if you want to know what C scale to play for a diminished sound on C7, let's write the E/G/Bb dim scale starting on C:


There you have it, the half-whole dim scale. Whole-half and half-whole are the same scale, just using a different note as your reference, or "starting" point.

OK, so maybe this isn't too far off from what I have been doing. It's sort of throwing in a diminished when you want a darker harmony; and you can get 4 different starting points (roots). Another explanation in the same thread is I think a bit truer to theory.

The naturally occuring triad of the 7th degree of a major scale is diminished. It can be thought of as an incomplete dominant 7th chord because if you played the 5th of the major scale under it, you'd have a V7 chord. Likewise if you added the naturally occuring 7th to that triad (the 6th degree of the major scale) you'd have a "half-diminished seventh" chord which can also be thought of as an incomplete dominant 9th -- add the 5th again under it and you get a V9.

Before the time of Bach (and in much of his music as well) , it was more common to hear these incomplete dominants than the full V7's we're so used to. Bach really began to establish the Dominant-Tonic progression that is the cornerstone of our harmony.

When you use a common diminished chord like #Idim or #5dim, they are usually substituting for secondary dominants (VI7 and III7 respectively). So if you went from I to #I to ii minor, the #I dim would substitute for a VI7 chord (the V of ii).

A half-diminished 7th chord naturally occurs as the ii chord in a minor key. As someone has already mentioned, it is often the ii chord in a minor key II -V -I. This will have a much different function than the vii7 in major.

People that only think about chords and harmony from a pop or jazz perspective should try and learn a little more basic theory and history. Before there were "chords" per se, there was the simple counterpoint of two voices, and then choral music using three voices or more. Each of these voices was singing or playing a melodic line of it's own and chords were the result of the interaction. We tend to think of chords as "blocks" under a melody, but this was not always the case.

I like this explanation. It recognizes the inherent fluidity in music and instrumentation. I wonder how we will be using chords in another fifty years, given the rapid advances in musical instrumentation and synthesis?


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