# Proper C diminished 7 chord note spelling?

I am reading this book called "jazz keyboard harmony",

here is a snippet from the beginning pages,

I know in the case of triple flat, which you don't use in music theory, you get to use another note name like in Cb diminished 7 chord, which is Cb Ebb Gbb Bbbb, you don't say B triple flat because we don't use triple flat, you get to say like Ab in this case

but outside of triple flat situations, I thought you always have to use correct note spelling?

In this example of C diminished 7, isn't it C Eb Gb and Bbb? Because we need a "third" from G to B, but in this book it's using C Eb Gb and A? Isn't this technically incorrect?

Yes, this is technically incorrect, and the seventh of this C diminished-seventh chord should in fact be B♭♭.

This text is just spelling it enharmonically for the ease of most readers, but the chord they have notated is technically an A diminished-seventh chord in first inversion.

And as for triple flats, those are very rare, but there's no real reason not to use them. If the situation calls for them—like, for instance, that C♭ diminished-seventh chord—you should be accurate and use them.

• For many things it's very useful to see Adim7 and Cdim7 as the same chord, particularly for jazz keyboard harmony. And guitar as well. I'm not sure if it makes any sense to think about these double chocolate things. In jazz keyboard harmony things are equal-tempered and enharmonic and all that, and in some ways the whole notation system is a hindrance and nuisance that has to be worked around. It is used because there's no alternative. To see the actual thing you need to look at the piano keyboard and forget about sharps and flats. My opinion only. Commented Apr 5, 2020 at 11:26

The whole point of a diminished seventh chord is that it contains that note. With root C, the major seventh is B, the minor seventh is B♭ and the diminished seventh is B♭♭. Technically speaking.

The (whole?) point of writing music down is to make it easy for others to read. In this example, it could be that the second premise comes into play. Or it could be plain ignorance - it's not the first time writers have written inaccurate stuff! In fact, for years, I thought that B♭♭ was actually an A!

For me, it would have been far better to explain which notes constitute Co7, and mention the fact that B♭♭ is enharmonic to A. It's being professional, after all. Particularly in any book designed to be called 'educational'.

• Inaccurate from a music theory geek point of view, but ... understood by readers! I put much more weight on the latter. :) Dim7 chords are a simple concept that can be taught to a child by showing the keys on a piano. You can even say, look, three semitones between every note. Easy. But why the A should be called "B♭♭" takes much more effort and with diminishing returns. Commented Apr 5, 2020 at 11:15

The 'correct' spelling of a dim7 chord includes the diminished 7th interval. So Cdim7 uses Bbb.

But this isn't as cut-and-dried as the 'don't dumb down the leading note of a scale because you're frightened of a double-sharp' thing. See examples below.

• IMO all those spellings are convoluted compared to "Cdim7". Commented Apr 5, 2020 at 12:44
• What? The whole point of a chord symbol is that it ISN'T spelt out! Though there's still the question of whether to call it Cdim7, Ebdim7, F#dim7, Adim7 or any of the enharmonic variants. Commented Apr 5, 2020 at 12:55
• Exactly. Now that piece of perspective has been recorded for future readers. The original post seems to imply that there's one spelling that's more correct than any other for all intents and purposes, and that the quoted spelling would be wrong even for the context where it was taken from. Commented Apr 5, 2020 at 13:21