A quick question to those who know better. I am looking at a Willie Nelson song and there are a few chords that I don’t quite understand, in particular the B flat dim 7 and a C sharp dim 7.
I’ve looked these up on the web and they seem to have the same fingering. My question is are they the same harmonically? And if so, does the naming have a significance? (there is no change in the key signature.)
BTW the song is “Crazy”
Thank in advance,
Glen
Glen, diminished chords - most often their extensions of m7b5 or dim7 - have a few uses in functional harmony.
I have just checked a few tabs for Crazy and it seems the use in that song is the same throughout.
The diminished chords are used as stepping stones, chromatic links to close the gaps between chords that are a whole tone apart and also give some voice leading.
Example:
C → C#dim7 → Dm7
The fingering you use will, in part, depend on the fingering (open or barre) you use for the chords on either side.
Yes. You can give or take three frets to every diminished chord and it stays the same, because the notes are identical, just in a different order. This technique is used a lot in Neo Soul and Lofi.
So… B Dim = C# Dim = F Dim etc…
I didn’t see a version of Crazy with Bbdim7.
Remember, diminished triads are built from the 7th scale degree of a major scale which is found a semitone below the root and its alphabetical name must be made from the letter one position below the root note letter name.
Using that knowledge, it is a simple step to think that Bb dim7 will come from the Cb major scale (key of Cb) and C# dim7 will come from the D major scale. (key of D). Well no. The diminished triad does (the plain dim chord) and the half diminished quadad does (the more commonly used m7b5 extension). But the diminished 7 is slightly different as it contains a diminished 7th (double flat 7) as its extension. It is not diatonic to a major scale. It is diatonic to the harmonic minor scale (in multiple repeats).
Diagram 1
D major scale (starting at the 7th scale degree C#) with diminished chords and their intervals below.
Note that the dim7 chord has something special going on. All intervals are minor 3rds (4 semitones) meaning its entire span is 12 tones (one full journey around the 12 position note circle).
Note that the diminished 7 chord (C#dim7) contains a non-diatonic note. I have labelled it as Bb. And that may raise an eyebrow or two because the chord now contains a note given as sharp and a note given as flat. And that rubs the wrong way. Surely sharps and flats do not belong together in the same scale or the same chord? Well, for our purposes here, we are going to have to live with that anamoly due to the chord formula for a diminished 7 chord.
C#dim7 = 1, b3, b5, bb7
Thinking about the C# major scale (C#, D#, E#, F#, G#, A#, B#) :
1st scale degree = C. All good.
3rd scale degree = E#. Flatten it = E. All good.
5th scale degree = G#. Flatten it = G. All good.
7th scale degree = B#. Flatten it two times = Bb. Mmh. Well, okay. It has to be done to maintain the strict rule on using all seven letters once only.
Let’s continue looking at the C#dim7 (with its Bb note) around the note circle.
All notes are equidistant, at intervals of a minor 3rd. This internal structure often leads to these chords being called symmetrical.
Look at the colour-coded boxes around the notes. Do you see how the very structure of a C#dim7 chord allows us to use the exact same notes and view it and name it in three other ways?
What this means is that the chords repeat up and down the guitar fretboard every third fret.
As @greenrider states …
Small point of correction. That should be diminished 7 not diminished.
Another necessary point of correction.
Bbdim7 = C#dim7 = Edim7 = Gdim7
Here are two commonly used chord shapes for the dim7 chord, on string sets A, D, G, B and then D, G, B, E respectively. I have shown these with root note as the lowest note to avoid any need to consider inversions. But each and every one can be seen as four chords within one chord shape (if taken as inversions) because they all contain the exact same notes.
Ricard, thank you very much for your detailed response, it makes more sense now. Also, thanks to @GreenRider I didn’t realize that that was how these chords worked. Based on what you said, I guess this could also be thought of as inversions.
Richard, the arrangement that I am looking at is from the Hal Leonard book “100 Most Popular Song for Fingerstyle Guitar.”
Here are a couple of screen shots that show where and how these chords are used:
The first occurs at bar 21
and the second at bar 23
and just for fun they throw in a G# dim 7 at bar 11
Again, thanks for the great response
Glen
Thanks for the reference to your source material Glen.
This …
tells me that there are going to be lots of chords and chord fragments where notes are altered and embellishments added to incorpate the melody and some harmonic movement.
Look at this small section and the low / top note movement.
With regard to the diminished 7 chords, they are a mix of full and partial chords. A partial chord can be implied by the harmonic and melodic context around it.
A full Bbdim7 chord.
A partial C#dim7 chord with melody notes - two of which (G and E) are chord tones played on the high E string.
A full G#dim7 chord.
Thanks for making that clear and for explaining it a lot better than I ever could. You are absolute correct, I should have taken the time to give it a thought instead of replying on the toilet. 
Haha.
It’s the modern way.
I have waited to be seated upon my own to make the most appropriate reply possible!
