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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 support
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).
