In the June 2010 Guitar Player (Jeff Beck cover), Andy Ellis has a lesson where he demonstrates how easy it is to go From C#dim to the F7, B7 D7 and Ab7 chords. That's cool, really, and it's in my head if not in my hands, but there's a key piece of information he fails to bring up.
Consider a chromatic scale.
C C# D D# E F F# G G# A A# BWe'll start from C#, as this is where Andy started.
C C# D D# E F F# G G# A A# BA diminished chord uses a minor third, so E.
C C# D D# E F F# G G# A A# BA diminished chord uses a flat 5, so G.
C C# D D# E F F# G G# A A# BA diminished chord uses a flat flat 7, formerly known as a 6 so A#. Well, we're talking flattening, not sharpening, so I should say Bb, but then I'd have to rewrite this chromatic scale.
C C# D D# E F F# G G# A A# BDo you see it yet?
Give it a moment. Now?
Bold normal normal Bold normal normal. A diminished chord is a stack of minor thirds. This means that a C#dim7 is also an Edim7 is also a Gdim7 is also a Bbdim7 (and it makes me wish I could type unicode on a Windows netbook keyboard to have that written as B♭°7 instead.
... wait ...
Anyway, if that one chord is four chords, and dropping the root a half-step gives you a dominant chord, of course you can jump to any of those four chords quickly.
But Sans, you might say, we play rock. How does this help us? And that's a good question. Some time around 1960, melody went from being notes in the chord to notes in the scale, and soon we went from expressive algebra chords to root-and-fifth power chords that allow you the maximum number of choices. (Gross exageration, but I believe that's the trend.) Diminished chords are elegant weapons for a more civilized age. But they do show up on occasion. Take "This Wheel's On Fire" from the Basement Tapes.
The chord is the second chord in the verse. "Meet again and wait". Take whatever diminished chord form and move it up a minor third at a time, 1-2-3-4, to get some cheap drama into the progression.
Considering going through "People Get Ready" to get Songquest on track.