I'd like to discuss symbols used to notate diminished and half-diminished chords in Music SE. They are often notated with an open or single-crossed circle.

Sometimes it is referred to as "zero", but typically in well edited scores the symbol is round, and of size similar or just a bit smaller than letter o.

Most often the symbol is written in superscript, but it is also often written at the same height as the main chord symbol, or even in the subscript, thus I'm not sure if a strict convention exists.

I tried to gather the various variants of chord symbols used in SE, and I compiled the following list:

  1. C0 (zero)
  2. C° (degree symbol)
  3. Co and Cø (superscript o and ø, see https://music.meta.stackexchange.com/a/3110/63781)
  4. Co and Cø (regular o and ø)
  5. Cdim and Cm7b5 or C-7b5

I see three main aspects of the chord symbols to consider. I'd also present my opinion on each of them.

Graphical presentation

  1. 0 looks ugly and it doesn't have a corresponding half-diminished symbol,
  2. ° seems too small to me, and it doesn't have a corresponding half-diminished symbol,
  3. o ø displays larger than ° and seems more appropriate, though it is also a bit stretched vertically, thus not round.
  4. o and ø displays round and nice, but has no vertical separation from the rest of the symbol
  5. dim and m7b5 or -7b5 are widely used, but much less compact and thus not liked by some

Symbols typed using html codes are not displayed correctly in comments, search results and titles.

Feasibility to input

  1. 0 easy
  2. ° can be input as a unicode character (difficult for some) or html code ° (not widely known either)
  3. o ø require using html codes <sup>o</sup> <sup>ø</sup> or <sup>&oslash;</sup>
  4. o ø easier to input than the above, especially the letter o
  5. dim and m7b5 or -7b5 easy

Feasibility to search in SE

  • 0, ° and o are not synonymous in SE search
  • superscript symbols can be found by SE search the same as regular ones
  • html symbols typed in search window don't work
  • In general searching the chord symbols is difficult, as searching for e.g. dim will return articles including dim, A#dim, A dim but not Adim
  • As various conventions are used by various people around the world, they might be searching for various versions of symbols

I presented you with 5 bad choices. I have three questions:

  1. Is there a strong preference for or against any of those?
  2. Are we confident enough about superiority of one convention over another to make edits like in this question: V→vii° or vii°→V where viio were replaced by vii°, which doesn't even seem to follow the highest voted answer in Typing musical signs!? I'd like to emphasize it is not my intention to point fingers or blame, rather to change things for better.
  3. What would be the steps to improve SE search system by treating some symbols as synonymous?
  • 1
    I tend to use 'dim', 'dim7', and 'min7b5' / '-7b5' for the searchability factor, but I know I've also used superscripts on occasion. I don't see a good way to standardize this (at least, not one likely to be implemented by SE), but my vote would go to the dim, min7b5 option.
    – Aaron
    Aug 30, 2021 at 1:53
  • I believe we've had similar Meta questions about sharps and flats: music.meta.stackexchange.com/questions/3058/… music.meta.stackexchange.com/questions/3560/… from my recollection, we never decided on one particular way to do it?
    – user45266
    Aug 30, 2021 at 19:29
  • @user45266 Yes, I recall that question. I wanted to ask specifically about the diminished and half-diminished chords. If we haven't decided which way to go, should we make edits like the one I mentioned? Aug 30, 2021 at 20:05
  • 1
    Personally, I dislike it when others use 0 for the diminished symbol. o is clearer, and the other options all seem more legit than the ambiguous zero ("what, a zero-octave pitch? Oh, never mind - that's a chord symbol").
    – user45266
    Sep 3, 2021 at 7:34

2 Answers 2


My biggest problem with this is that I don't think that we should be trying to set site-wide policy on the styles that people choose for notating chords (and probably other things, for that matter). "Are we confident enough about superiority...." -- Musicians certainly have differing opinions on these conventions out in the real world, and I don't know why that should be any different here.

I'd say that you should edit posts that you think can be substantially improved, but don't go on a hunt for things to fix. If someone made an edit like this to one of my posts, I would roll it back if I didn't like the change; I presume that others can make the same judgement on their own posts.

To put a finer point on things:

1: (C0) I don't recall ever seeing this on SE Music (not that I am saying that it hasn't been used); it seems reasonable to edit this, in my opinion.

2, 3, 4: (, Co, Cø, Co, ) My feeling is that changing from one of these styles to another does not rise to the level of a significant edit.

5: (Cdim, Cm7b5, C-7b5) I think that you should not change these at all, especially the m7b5 chords. Some people prefer calling these m7b5 chords over calling them half-diminished; let's not step on their wishes.

My personal preference is to use any of Cdim, Cdim7, Cm7b5, or C-7b5. In general, I prefer ASCII to Unicode musical symbols when possible for accessibility, readability, and searchability. I came around to this way of thinking when writing an answer to this earlier SE Meta question. The issue of Unicode symbols not rendering for everyone has come up several times since then, for example in this question, also linked by @user45266 above.


Hm... I feel like I'd be in favor of encouraging users to simply spell out the full words whenever possible, "diminished," "half diminished," "augmented," etc. This is also the most intelligible, especially to readers without a firm fluency in chord degrees and symbols. (We have to assume certain minimum levels of music literacy, or else we'd start everything at the beginning, but it's nice to avoid shorthands where we can.) It helps searchability, too, since any user (but especially one just introduced to diminished chords) who wants more information on the subject is likely to type in diminished chords, but unlikely to think to try 0, o, or for that matter ø.

Obviously there are times that spelling it out is impractical—it's more appropriate in a sentence of text ("The C half-diminished chord in m. 10 is..."), but when giving a chord progression as a sequence of symbols it's unwieldy ("C - D diminished - G - C"). But these are more illustrations, right? Hopefully any answer that includes this kind of progression also contains prose discussion, and maybe it could be spelled out there?

At any rate, I would prioritize clarity to the reader over searchability, so:

  • C0: Agreed, is maybe the least clear option, and the most likely to make me think of carbon monoxide.
  • C°: Agreed, too small and has no allowance for half-dim.
  • Co and Cø: To my mind, this is the second-best option, clearest to the reader if we are using symbols rather than words, and the closest to the ideal. Also the least likely to be mistaken for actual words.
  • Co and Cø: This runs the risk of creating confusion with two-letter words: "Do," e.g. the solfege syllable, a confusion I genuinely experienced a few minutes ago; or "Co." as an abbreviation for "company," or "Go" for the word "go," etc. A reader without a firm grounding in scale degrees might be the most confused by this form ("And what's that Swedish word?").
  • Cdim: To my mind, this is the very best option—at least for fully diminished sevenths and for triads. I don't see it as a great solution for half diminished, though. I'm not used to encountering "C-7b5", and would be honestly thrown for a loop by it, even though I'm a professional musician who, I like to think, paid moderately good attention in theory class (maybe the issue is that I'm too much of a classical boy and not a jazzer?). To my mind this crosses from "assuming a basic level of musical literacy" into "assuming either that someone is not just a performance major but a theory major" or "assuming literacy in a certain context." But then again, what's so bad about: "C - D half dim - G"?
  • 1
    Yes, C-7b5, or Cm7b5 or Cm7(b5) are often used in jazz scores. Concerning your last point, do you question usefulness of chord symbols in general? Mar 4, 2022 at 18:42

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