Comments re: diminished 7 chords
If you look at the major minor system, the only place you find fully
diminished 7 chords is viio7 in a minor key. Traditionally (Bach to Tin Pan
Alley) the chord is used functioning to point to the i chord in minor.
However, confusion usually ensues because of enharmonic spellings and the
fact that it can and often does resolves in a deceptive cadence.
In the progression: F - F#o7 - Gm7 - G#o7 - Am7, found in many tunes like
"It Could Happen To You" and others, you could analyze the chords as I -
viio7/ii - ii - viio7/iii - iii. For the I, ii and iii chords you are in
the key of F major, so the notes of the F major scale work. For the F#o7
(viio7/ii) you are in the key of G minor, and we derive harmony from the
harmonic minor scale, so the G harmonic minor scale sounds correct. For the
G#o7 (viio7/ii) you are in the key of A minor, so the A harmonic minor
scale sounds correct. The F#o7 is essentially taking the place of D7b9 the
V of G minor, and the G#o7 is standing in for the E7b9. Either way, the
chords point the way, tonicizing the next chord.
Sometimes these chords are difficult to determine which key they are from.
Often the G#o7 is written as an Abo7. An Abo7 chord is the viio7 of Bbb
minor, the relative minor to Dbb major, with a key signature of 12 flats! I
don't know about the rest of you, but I would rather think no sharps of
flats than 12 flats.
Other times the diminished chord may be in an inversion, but written as if
it is not. For example: Cm/Eb Do7 Cm. (i6 - viio7 6 - i). The shorthand is
to write the diminished chord as a Do7, but in this context it may be a
Bo7. What's the difference? The actual chord spelling use the same
enharmonic pitches, but while Bo7 is the viio7 of Cm, Do7 is the viio7 of
Eb minor. In the passage, using a C harmonic minor may be the more musical
choice.
There are times the diminished chord may not resolve as expected which can
cause some confusion. In the first few measures of "The Song Is You" the
chords are:
C - D#o7 - Dm7. How can the D#o7 point to Dm? It doesn't; it points to Em
and deceptively resolves to Dm7. The progression is I - viio7/iii - ii, and
the E harmonic minor sound works over the D#o7 chord. (The D#o7 chord is
sometimes spelled as Ebo7, which would be the viio7 of Fb minor!)
There are times when the diminished 7 chord sounds good using a octatonic
scale, (A.K.A.: diminished scale, whole-half, symmetrical scale). So for a
Bo7: B-C#-D-E-F-G-Ab-Bb-B. Using it arbitrarily would not be good as you
may notice. If traditionally the Bo7 is suppose to point to C minor, then
the C#, and E notes are, at best, ambiguous to that key, while the
F-G-Ab-Bb sound natural.
Sorry if I went on too long, but it is in the interest of clarity.
Sometimes answers that are too brief can lead to misunderstanding. If
anything here is unclear, please let me know.
Thanks
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Bert Ligon
Director of Jazz Studies
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School of Music
University of South Carolina
Columbia, SC 29208
Voice: (803) 777-6565
Fax: (803) 777-6508
bligon@mozart.sc.edu
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