Watch the Diminished online guitar lesson by Fareed Haque from 1-2-3 Bossa Nova
Ah, diminished chords! Demented perverted debauched harmonies of delicious duplicity! Come hither little ones and enjoy the wicked pleasures of harmonic complexity at its silliest and most scrumptious! It's so hard to explain diminished chords, but once you get it it's like seeing the world of chords and harmony through a kaleidoscope - at once one thing and many things all reflecting upon and enriching each other. Remember this: A diminished chord is a dominant 7b9 chord with no root. G dim7:1-G, b3-Bb, b5-Db, bb7-Fb = C7b9 no root: 5-G, b7-Bb, b9-Db, 3-E. But here's the tricky part (or the simple part depending on how your mind works) since a diminished chord is composed of all minor 3rd intervals, any note in a diminished chord can be the root, the remaining notes becoming the b3, b5 and bb7. And since a diminished chord is a dominant 7b9 w/no root, then each diminished chord grip can be 4 dominant 7b9 chords too. If you don't believe me, my pretty, then check it! G dim7 - G, Bb, Db, Fb = C7b9 no root - G, Bb, Db, E; Bb dim 7 (same as G dim7, right?) = Eb7b9 (G, Bb, Db, Fb or E again!) Db dim7 (still the same as G dim7, right?) = Gb7b9 ( G, Bb, Db, Fb or E again!?! Yes! Again.); and finally E dim7 (still the same as G dim7) = A7b9 (G, Bb, C#, E).
So any diminished chord grip can be 4 diminished chords and 4 dominant 7b9 chords all at the same time. Take two aspirin, get a heating pad and a hot water bottle, and call me in the morning.