Q: I see chord formulas (Hal Leonard guitar instruction books) that I use to create chords, but when I see illustrations of chords elsewhere, I see notes that don't appear in the chord formula.
Here is a specific example: Bdim chord consists of the tonic, flatted 3rd and flatted 5th, (this is B, D, F) but illustrations of the chord add Gsharp. Why? More importantly, HOW is it established that Gsharp is added?
I'll tell you what I do know: to build the vii chord triad of the Major Scale in C (we discover this is Bdim), we select a subsequence of notes from the Major Scale in C starting at B. The sequence is formed from notes 1, 3, and 5, so from C,D,E,F,G,A,B we obtain B, D, and F. What is the relationship of G# to these three?
Gsharp/Aflat is not a note in the Major Scale in C, so it is not merely the 1,3,5 pattern in the notes of the Major Scale in C continued to 7. But, when I look at the staff itself, I see the next higest place available to write in a note above B, D, and F, is Gsharp. Interesting.
What is going on here? What is the pattern?