Hey Friend,
I know I'm running a little late today with the lesson. I took today off to take care of some things and while I was putting today's message together, I was listening to Boston's "Don't Look Back" album.
I should know better! I've got my studio headphones on and the sound is epic - my ears are in heaven. I'm in critical listen mode, trying to isolate various guitar parts, and when I manage to pull back a little, I find myself air drumming along with each song. I can't help it!
The final chord in the G major harmonic progression is F# Diminished (F#°). It is the VII° chord (seven chord), and you won't see it very often at all in Rock, Blues or Country! If you like Jazz, there are more opportunities for diminished chords, so you may as well learn it so you're well rounded.
As a review, here are the chords we've covered so far in G major:
I IIm IIIm IV V VIm VII° G Am Bm C D Em F#° Diminished chords can be constructed from the major scale of the key. In the case of F#°, the notes are F#, A and C. Now don't confuse this with the fact that chord construction is based on the key of the chord name. F#° is built out of the F# major key, which has these notes:
F# G# A# B C# D# E#
A diminished chord takes the tonic from the key (F# in this case) and adds a flattened third and fifth notes. So it has a minor chord flavor, but that flattened fifth adds some extra wonkiness. That gives us the notes F# A C as the 1 3m 5m notes.
Since those three notes occur naturally within the key of G major, F#dim works out here. Here's G major again, in case you still don't believe me:
G A B C D E F#
Here are the major keys where you find F#°:
Key I IIm IIIm IV V VIm VII° G G Am Bm C D Em F#°
And the minor keys:
Key Im II° III IVm Vm VI VII Em Em F#° G Am Bm C D
Easy enough, right? Here are the exercise files for you to play with. Tomorrow we'll look at the various inversion and neck positions for F#°. Have a great one!
Peace~
Dave | 
