The full diminished 7th chord consists of Two calculations. TWO distinct components that are separate items.The full diminished seventh chord consists of an additional minor third stacked on top of the other minor thirds.If you use the(1)RELATIVE minor of C major(2)in the HARMONIC MINOR MODE(3)and build the chord on the vii scale degree, the notes for the full diminished seventh chord, with the diminished seventh interval added, will be G#, B, D, F. Each of these notes have a distance of 1 1/2 steps, or 3 frets, between the note and the next adjacent note.
This is where the distinction gets fuzzy for some guitarists. The full diminished seventh chord has the same spacing between all of the notes. When the notes are moved around, (or inverted) the chord becomes ambigious as to what the REAL name of the chord is called.The actual name of the diminished 7th chord depends on what SCALE the diminished 7th is formed in, or what key was it constructed in.
The harmonic minor mode starting on A consists of the notes A, B, C, D, E, F, G#, A.The vii scale degree of the A harmonic minor mode (scale)is G#. The vii chord produces the notes G#, B, D, F.
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Here is a GENERALIZED RULE for identifying the actual name of any diminished 7th chord.
If you know what key you are in, the alphabetical name of the diminished 7th chord should have been derived from the seventh degree of the scale belonging to that particular harmonic minor key.
The previous example named the chord as G#dim7. The G# is the 7th degree of the harmonic minor scale with "A" as the octave, or 1st degree, or tonic, or starting point.
IT IS INCORRECT TO REFER TO THE STARTING TONE OF ANY SCALE AS THE "ROOT". TONIC, or 1st scale degree, is the term that is normally used in the larger musical world of musicians, other than GUITARISTS.
