The table for guidance

I find this guide really useful until I find it kinda weird and "wrong" to apply it on key like C sharp half-dimished or diminished chords. I find that I have to double-flat C natural to get the Bb for a C#dim7 , or just single-flat the C natural to get a B nat for a C#half-diminished chord. Just to make sure, a C#half-diminished chord consists of note c#, e, g, and b, right? I am very confused , I might have left out something but this is a main issue for me, is it because of the key with its tonic on the black keys?


Your problem started when you thought the 7th note (leading note) in C# major is C. It can't be C, as that would have two different notes with the same C name, to be written on the C line or space on the stave.

That leading note is actually B#. Although enharmonic to C, its name here is B#. As in every note of the C# scale is the same as the C scale, but sharpened.

C# diminished then becomes spelled as C# E, G, Bb. The Bb being a tone lower that B#. C# half diminished then becomes C#, E, G, Bnat. The Bnat. being one semitone lower than the leading note, B#.

Other names are available for the dim. chord itself, but the spelling is here for C#o.

| improve this answer | |
  • @DavidBowling - well spotted ! And with a 50/50... Almost worth a downvote! Someone missed the opportunity...I daresay not you, you're above that. – Tim Jul 12 '18 at 12:56
  • I knew the leading tone is B, but thinking of the Bb and B notes, I thought I had to make C the "replacing leading tone" to get a Bb and B. That's my problem. That's why I found it weird at first, I was confused so I asked. – Yau Qi Herng Jul 12 '18 at 12:56
  • Yes, except the leading note in C# Is B#, rather than B. – Tim Jul 12 '18 at 12:58
  • 1
    Leading note in C# major *and C# minor is still B#. – Tim Jul 12 '18 at 13:11
  • 1
    Yes, because unless that 7th note in the natural minor scale is raised (as in harmonic min.) it can't be a 'leading note'. – Tim Jul 12 '18 at 13:33

You seem to have made a mistake somewhere.

C diminished 7th is C Eb Gb Bbb.

C# diminished 7th has all the notes one semitone higher: C# E G Bb

C half diminished 7th is C Eb Gb Bb.

C# half diminished 7th is C# E G B

Note that there are only three different diminished 7th chords (at least, in equal-temperament tuning) and each one can be "spelled" in different ways. The following are all the same notes:

C Eb Gb Bbb

Eb Gb Bbb Dbb

D# F# A C

Gb Bbb Dbb Fbb

F# A C Eb

Starting on Bbb doesn't work in practice, because you need a "triple flat" for the 7th:

Bbb Dbb Fbb Abbb

But starting on A works OK, of course:

A C Eb Gb

These alternative spellings "explain" why diminished 7th chords are very useful for modulating quickly between almost any pair of keys.

| improve this answer | |
  • And so Major keys are made to be the basis, and then looking at whether the chords are minor, 7th (or any added notes of the chord), diminished or half-diminished, and other additional notations to the chord. Am I right to have this concept? – Yau Qi Herng Jul 12 '18 at 11:53
  • "You seem to have made a mistake somewhere." -- I am not sure what mistake you are referring to; OP spelled C♯∅ correctly as C♯ E G B. The business about flatting and double-flatting "the C natural" to get a B or B♭ doesn't make sense, maybe that is what you are talking about? – ex nihilo Jul 12 '18 at 11:59
  • @DavidBowling "maybe that is what you are talking about" - yes, that's what I was talking about. – user19146 Jul 12 '18 at 12:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.