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?Bdim chord triad with Gsharp addedenter image description hereenter image description hereenter image description here

  • Can you provide the illustration you refer to that has a G#? Curious to know if it specifically says "G#" (vs A♭) or if it's a guitar-chord diagram showing a finger position without naming the note. – mistercoffee66 Nov 17 '19 at 22:30
  • in this chord (if you mean vii°7) the flat of Ab is lacking. – Albrecht Hügli Nov 17 '19 at 22:50
  • If this is supposed to be in the key of C then it's a B min7 b5 or half diminished b, d, f, a. But then the symbol is wrong. – ggcg Nov 17 '19 at 23:29
  • I have added an image of the chord formula and an image of the illustrations shown in the a separate chord book. – John Nov 18 '19 at 0:49
  • I see, thanks. These are full diminished 7th chords as I described in my answer. – ggcg Nov 18 '19 at 0:55

To answer your question of "why" it is added in the fingering diagrams, it has to do with convention. In jazz, a diminished symbol (°) is often shorthand for diminished 7 (°7) in sheet music even though that is technically imprecise (as explained in the other answers). I would say in this context -- ie not sheet music but something meant to be instructional, the fingering diagram you have is wrong and should omit the G#/Ab or label it as B°7.

The diagram further confuses the issue by labelling the additional note as G#, whereas it should technically be Ab to reflect that the note is functioning as a 7th to the root of B.


There is a difference between a diminished triad and a full diminished seventh chord. The dim triad is (1, b3, b5) but the full dim chord has a double flatted seventh (1, b3, b5, bb7). Strictly speaking the G# is not correct from the perspective of classical music theory as G is not the seventh of B but they are enharmonic so some texts may equate them. I got points on in the 80s in music theory if I use enharmonic tones in chord construction.

Based on the info you provided I cannot determine if your book is truly wrong or if you have misinterpreted two different definitions.

  • I have added the images to my original question. The formula appears in the Hal Leonard Guitar Method Book 3 (2nd ed), and the chord illustrations are from the Hal Leonard Incredible Chord Finder book (2nd ed). – John Nov 18 '19 at 0:51
  • I see, thanks. These are full diminished 7th chords as I described in my answer. – ggcg Nov 18 '19 at 0:56
  • Hi ggcg, I added an image showing where that B dim chord image came from. Please let me know if this changes anything. Thank you for your help. – John Nov 18 '19 at 1:10
  • It supports my answer. That new picture of the triads in the key of C, not 7th chords. The other pics of of the dim 7 chord, a different beast. – ggcg Nov 18 '19 at 1:18
  • Thanks ggcg, with your answer as a hint, I worked that out myself on paper so I could see it plainly, and indeed, from the same list of chord formulas the next formula; 1, b3, b5, bb7; provides the "diminished seventh". My chord book is not sufficiently rigorous. – John Nov 18 '19 at 2:12

B, D, F is B diminished. B, D, F, A♭ (or G♯) is B diminished 7th.

This 4-note chord has a special property - it's symmetrical. It's a pile of minor 3rds. But add another minor 3rd - G♯ up to B - and we're back where we started! Bdim7 is the same notes as Ddim7 as Fdim7asAb dim7. And it's full of tritones - the augmented 4th/diminished 5th interval that powers a dominant 7th chord. I won't give the full lecture on diinished 7th chords now, just know that they're very useful for slipping into a new chord or even a new key.


vii° is a B<5 triad (B,D,F,) as notated in the staff of your example.

What you're asking for is vii°7 B dim7 or B°7 (B,D,F,Ab)

As the dim7 chords can be used as enharmonic exchanges it might be also spelled as B,D,F,G# but more logical would be G#,B,D,F.

  • Hello Albrecht, I have added images from my instructional books. Please let me know if this changes anything. Thank you for help. – John Nov 18 '19 at 1:13
  • Nein, es ändert sich nichts: Entweder ist die Belegung falsch oder die Akkorddiagramme stimmen nicht überein. Actually the oter answers are similar. The mean all the same! For this I’m gonna vote them up now – Albrecht Hügli Nov 18 '19 at 6:33

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