Diminished chords question

Like a number of folks here, I am re-visiting Uncle Rod's Boot Camp to boost my chord transition skills. I haven't used diminished chords very much in the past, but am liking the way they sound, and am happy to learn that they appear to be barre chords, which means that I can use the same chord shape up and down the neck. My question is this: If a Cdim chord is 2323, why would an Fdim (or Abdim) be formed as 1212? I would have thought that 1212 would be a Bdim chord. And since we are on the subject, why is an Fdim equivalent to Abdim? Many thanks.

We had this discussion a few days ago... This was my contribution to that thread:

The basic building block interval of chords is the THIRD. A major third is four half steps (i.e. C to E). A minor third is three half steps (i.e. C to Eb).

If you start with a major third (C-E) then stack a minor third on that (E-G) you get a major triad (three note chord).
If you start with a minor third (C-Eb) then stack a major third on that (Eb-G) you get a minor triad.
Two major thirds give you an Augmented Triad (C-E-G#).
Two minor thirds give you a Diminished Triad (C-Eb-Gb).

If you stack on another third on top of the triad, you get a 7 chord - the variety of which depends on the combination of major and minor thirds (CMaj7, C7, Cmin7, Cmin7b5 [also known as half diminished], and Cdim7.

A diminished 7 chord consists of three minor thirds stacked one atop the other (C-Eb-Gb-A). Because there are only 12 tones in the chromatic scale - and 12 is divisible by three - if we were to stack another minor third, we arrive back at the root (one octave higher) - C-Eb-Gb-A-C... and so on. This unique bit of math means that the same four notes are used for (in this case) Cdim7, Ebdim7, Gbdim7, and Adim7... So, no, Uncle Rod did not steer you wrong.... and yes, it is easier to just use the repeating dim7 chord shape than worry about playing a plain old diminished triad.

http://en.wikipedia.org/wiki/Diminished_seventh_chord#Diminished_seventh_chord_table

If I'm reading this right, the construction of a diminished chord--in this case, a diminished 7th chord--requires:
Root + Minor Third + Diminished Fifth + Diminished 7th (not major 7th)

But flatting a 7th is double flatting a maj7 ... aka you always go to major 6th.
http://www.pianochord.com/C-diminished-7th/variation/C-diminished-7th-flat-5th

So for a Cdim7 you get: C Eb Gb A
Root: C
Minor Third: E -> Eb
Dim Fifth: G -> Gb
Dim 7th: Bb -> Bbb or "A" (Maj 6th)

Let's do the same for Fdim: F Ab B D
Root: F
Minor Third: A -> Ab
Dim Fifth: C -> Cb or "B"
Dim 7th: Eb -> D

And the same for Abdim (also G#dim): Ab B D F
Root: Ab
Minor Third: C -> Cb or "B"
Dim Fifth: Eb -> D
Dim 7th: Gb -> F

If you notice, the notes that build the diminished chords for F and Ab share the same four notes. So are they the same things? Sort of--the only remarkable difference is the designation of the root note. The bass note so to speak for an Fdim will be the F, while for Abdim it will be an Ab.

This brings us to the ukulele. We have four strings and roughly 2 octaves to work with. Our lowest note is a C for re-entrant tuning or a G if you have linear tuning. Playing Fdim and Abdim both as 1212 is acceptable because we play the same notes, same chord--just in a different voicing. In order to pull off the chord as written, we'd have to search up our fretboard and start with F as the root and fit the other notes around it. If you try it, you will find that 4545 works too. But wait--if you move up 3 more frets...7878 also works!

If the light bulb hasn't clicked already, let's look at Bdim: B D F Ab

Root: B
Minor Third: D# -> D
Dim 5th: F# -> F
Dim 7th: A -> Ab

So you would be correct--1212 covers all of those chords! Funnily you forgot to mention Ddim which 1212 is most like if you consider D to be the root and you build the other notes around it. Hope this helps!

you take a major 7th chord and diminish all but the root, so you can take any chord a half step lower, except the root stays the same. So for a C#dim you play a C chord, with the root remaining C#. For those of us without bass notes, it's the same as playing a flat 9 chord of the one below. So C#dim and C7b9 are the same, except for the bass note, which is not our responsibility.

A frequent use of a diminished chord is to vamp between a chord and the diminished of the next step up, so try holding a 7th chord steady but augmenting the root note up one. C7-----C#dim7--------C7-------only difference is the C changes to C# and back.

They never resolve anywhere so if you want to keep people in suspense, just hold that same shape and move it up and down the neck, plus you will sound very intelligent and avant-garde.

A diminished chord can be named after any of its notes, so their nature is usefully ambiguous..... they are slightly tense sounding, and are nearly always transitioning to some other destination of relief, thereby assisting the movement of your chord progressions and making them more interesting.ie the progression would work without them, but wouldn't sound as classy.

These comments made my head explode a bit at first (I'm fairly dense when it comes to music theory), but in the end it's a lot clearer to me now. Thanks, everybody!

Strumdaddy said:

A diminished chord can be named after any of its notes, so their nature is usefully ambiguous..... they are slightly tense sounding, and are nearly always transitioning to some other destination of relief, thereby assisting the movement of your chord progressions and making them more interesting.ie the progression would work without them, but wouldn't sound as classy.

Click to expand...

Winner! An ukulele diminished chord can be named after any of the notes played. Also, if you move a diminished chord up or down by 3 frets, you have the same diminished chord repeated.

Chikon2000, I like Diminished chords as well

I like this last description/explanation from John Sargent above:

"Winner! An ukulele diminished chord can be named after any of the notes played. Also, if you move a diminished chord up or down by 3 frets, you have the same diminished chord repeated."

This is probably not kosher from a Music Theory standpoint, and absolutely no help to any Bass players, but oftentimes when I'm writing out chords on lyric sheets, I use a 1 with a 'degree' circle, or a 2 with a 'degree' circle, or a 3 with a 'degree' circle to indicate 1st, 2nd or 3rd position Diminished chord forms. I do that because I know the 0101 chord shape as Gdim and I call it a Gdim even when it's not correct or accurate to do so. Same with 1212, which I know as an Fdim or Ddim, OR 2323, which I know a Adim or Cdim. In other words, when I want to designate the use of a Diminished chord, I find it easier (and more helpful) to identify it by its chord shape rather than its exact Musical name.

Sorry, Bass players and Music Theorists who may take umbrage at my misuse of proper chord names when doing my song sheets.

keep uke'in',