Watch the The Diminished 7th Chord Pt. 1 online guitar lesson by Brad Carlton from Guitar Lab: Diminished Moves Vol. 1
The diminished 7th chord is an equal interval structure consisting of four notes spaced evenly in the chromatic scale by minor third intervals. A minor third is three half-steps (frets). One octave consists of 12 half-steps, so 12 divided by 3 equals 4. This equal interval construction gives the diminished 7th chord it's lack of harmonic stability. This course examines the various resolving tendancies for the dim 7 chord.