THE MISSING ROOT
In spelling it as a diminished triad in root position,
it can be seen that the three tones which spell the 'C' diminished button
(A-C-Eb ) indicate the 3rd, 5th and 7th of a dominant chord with the root
(F) omitted.
Now, in order to complete the dominant 7th chord, by causing
the missing root (F) to sound, it is necessary to add a bass button, or
another chord button. This can be done in various ways as follows:
A) Play 'C' diminished button
with 2nd finger and 'F' fundamental bass buttons with 4th finger:
B) Play 'C' diminished button
with 5th finger and 'F' (e#) counterbass button with 2nd finger (This will
sound as in A:)
C) Play 'C' diminished button
with 2nd finger and 'F' major chord button with 4th finger:
D) Play 'C' diminished button
with 2nd finger and 'F' 7th button with 3rd finger; (this will sound as
in 'C')
DEFINITE PURPOSE
Although the beginner may wonder why we would ever consider
these roundabout ways of producing a dominant 7th chord, the advanced player
and the would-be accordion transcriber should know that each and every
way has definite purpose for technical -and- theoretical reasons.
For instance, employing the two buttons as described in
(A) in rhythmic form, and with the melodic progression of G-Gb-F played
in the right hand, this would sound much better, and would be more correct,
than if the 'F' 7th button were played instead of 'C' diminished button.
In other words, this is the manner to perform a dominant 7th rhythmic accompaniment
when the composer indicates the root omitted on the upbeats.
MODULATION
(b) COULD SERVE THE SAME PURPOSE, BUT IS MORE IMPORTANT
AS A SUBSTITUTE POSITION ON THE KEYBOARD WHEN A FOLLOWING PROGRESSION IS
OF A modulatory NATURE, SUCH AS PROGRESSING TO ANY OF THE FOLLOWING:
To E7th chord, E Bass; To B7th chord, F# Bass; To F#
major chord, F# Bass
(C) and (D) are optional within each other and are useful
mostly in progressions of C chord B button combinations. For instance,
sustain "C" diminished button with the 2nd finger while progressing from
'F' major chord button (4th Finger) to 'Eb' diminished chord button (5th
finger). 'F' 7th chord button (3rd finger) can be substituted for
'F' major chord button.
The diminished button presents still other harmonic possibilities
and I shall endeavor to illustrate them in my next article.