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The question below is referred to W. Leavitt - Getting up there (duet), Vol. 2

The piece is in key of C. In the last system, upper staff, we have the following chord progression:

C A-6 A-7 F Gdim G7 C

In terms of functional harmony, what role does that Gdim play?

I found:

I VI6 VI7 IV Gdim? V7 I

Thank you for your supportenter image description here

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  • 1
    Appears to be for guitar(s).
    – user70304
    Aug 29 '20 at 0:15
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Steven Laitz calls this a common-tone diminished seventh chord, which is labeled "c.t.o7 to distinguish it from other uses of diminished chords.1 (See also Wikipedia's Diminished Seventh chord: other functions.) Its function is to "maintain the root of the harmony they extend".2 Here is a reproduction of Laitz's Example 35.17A, which illustrates the process:

X:0
T:Steven Laitz, The Complete Musician, 2008
T:Example 35.17A (p. 820)
K:A
M:none
L:1/4
%%score V1 (V2 V3)
[V:V1] "A:"y "I"E y "c.t.o7/V"E- y "V43"E
[V:V2 clef=bass] y [A,C] y [=G,C] y [^G,D]
[V:V3 clef=bass] y A,, y ^A,, y B,,

1 Laitz, Steven G, 2008, The Complete Musician, New York: Oxford University Press, p. 820. Laitz is not alone in this. For example, see Aldwell, Edward, and Carl Schachter, 1989, Harmony and Voice Leading, 2nd ed., Fort Worth: Harcourt Brace Jovanovich College Publishers, pp. 516–519.
2 Ibid. (Laitz's italics).

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  • Reading the resource you kindly provided, I find that in the case of my example that G°7 chord (or Bb°7 chord) is the #vi°7 resolving to V7. Is it right?
    – LeoAn
    Aug 29 '20 at 10:19
  • @LeoAn My apologies for missing your question until now. The chord is labeled C.T.o7 in order to avoid the problem of assigning it a scale-based name. So while one could think of the chord as being built on #6 (or #1, 3, or 5, or any enharmonically equivalent pitch, like b7), that scale degree (and others) either aren't assigned a meaning in tonal theory, or their meaning doesn't align with the role of the common-tone chord. C.T.o7 clarifies the role of the chord without ambiguity.
    – Aaron
    Mar 19 at 22:06
  • @LeoAn You might also find this Q&A regarding #vi helpful: Name of #vio7 in chord progression?.
    – Aaron
    Mar 19 at 22:08

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