On Wikipedia it says:

Some of the symbols used for chord quality are similar to those used for interval quality:

    m, or min for minor,
    M, maj, or no symbol (see rule 2 below) for major,
    aug for augmented,
    dim for diminished.

In addition, however,

    Δ is sometimes used for major,[a] instead of the standard M, or maj,
    − is sometimes used for minor, instead of the standard m or min,
    +, or aug, is used for augmented (A is not used),
    o, °, dim, is used for diminished (d is not used),
    ø, or Ø is used for half diminished,
    dom is used for dominant.

Is it just tradition or is there a good reason why A and d are not used for augmented and diminished?

  • 10
    Mainly because A and D are used for chord names; it would be confusing to use them to describe the quality of the chord as well – Shevliaskovic Apr 15 '15 at 8:58
  • If that is the only reason, I use it. (I am programming something.) – user19822 Apr 15 '15 at 10:56
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    If you are programming something where you expect users to type the an identifier for a chord, please do not us A or D, as these letters will then have two meanings, depending on context. It will be difficult to parse the instruction and difficult to write it, too. – AJFaraday Apr 15 '15 at 14:40
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    I'm not sure what the problem is with those characters as you can look for and display the + and ° characters in pretty much any language. – Dom Apr 15 '15 at 18:19
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    "Not too confusing" seems like poor reason to buck convention. Might as well call your notes A-L instead of having sharps and flats. – user28 Apr 15 '15 at 21:14

M cannot be confused with the letter name of a note, whereas D and A can. The + is probably due to the interval (usually 5th) being larger than original by a semitone. That being the case, dim could be -, but that is sometimes used to denote minor , NNS uses it. Why o, not a clue! There isn't even an o in the word!

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Others mentioned the possible confusion with note names. And indeed, in some German songbooks (like the 1909 "Zupfgeigenhansel") you might find Cv instead of Cdim (v for vermindert), with v not being in competition with a note name.

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