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I came across several guitar chords which seem to be 'diminished' chords:

  • X°7
  • Xø7

I read some articles that might provide useful informating, including the Dutch Wiki article Chord (music), and several others.

According to the caption Chord symbols and terminology from the Wiki article Half-diminished seventh chord, the symbol ø is invented to distinct a diminished triad plus a minor seventh and a diminished triad plus a diminished seventh.

I came to the following:

  • According to this webpage, Cø is CE♭G♭B♭.
  • According to the Dutch Wiki article, C° is CE♭G♭.
  • According to that same article, Cø7 is CE♭G♭B♭.
  • C°7 is CE♭G♭B♭♭.

But wait. Both Cø and Cø7 are mentioned, but they exist of the same notes. What is the difference between those two chords?

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3 Answers 3

up vote 1 down vote accepted

A half-diminished chord has a root, minor 3rd, diminished 5th and a minor 7th (eg. A C Eb G). The minor 7th is implicit in a half-diminished chord. So it is not necessary to include the 7 after the half-diminished sign (ø). And so, yes, both notations will refer to the same chord. In other words if a chord is named, for example, Cø7, the 7 is redundant.

A diminished triad has a root, minor 3rd and diminished 5th (eg. A C Eb). A diminished 7th chord has a root, minor 3rd, diminished 5th and a diminished 7th (eg. A C Eb Gb). So, it is advisable to be clear about which of these is required. So A° denotes an A diminished triad (A C Eb) and A°7 denotes an A diminished 7th chord (A C Eb Gb). However, there is still some ambiguity: in actual music, a diminished sign (°) can implicitly suggest a diminished 7th chord, whether the 7 is included or not.

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There are three types of diminished chords, Cø and Cø7 are the same. Some people just notate the chords slightly differently because how they learned the chords.

A diminished triad is denoted with just a °, i.e. C°, and it contains a root, a minor third and a diminished 5th.

A half diminished seventh is denoted with a ø and it is also common to see a ø7 because it is a seventh chord but a half diminished chord will always have a seventh. So you could use Cø or Cø7. Whichever one you see, they contain a root, a minor third, a diminished fifth, and a minor seventh.

A fully diminished seventh is denoted with a °7, i.e. C°7. They contain a root, a minor third, a diminished fifth, and a diminished seventh.

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The Cø7 is also known as Cmin7b5, spelled 1-b3-b5-b7. The C°7 is spelled 1-b3-b5-bb7. While the dim triad and min7b5 may be found in the major, natural minor, and melodic minor scales, the °7 is derived from the seventh mode of the harmonic minor scale.

You may frequently find the ø in jazz tunes, however the °7 is less common because it is loaded with tension. An interesting feature of the °7 is that it is symmetric -- any of its four voices may be treated as its root. That symmetry lends itself to sliding this chord in minor third intervals, just as the old Looney Tunes cartoon soundtracks did. 8^)

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Not sure about the harmonic minor reference - there's no b5 or bb7 in it.There's a b6 and a maj 7, not the same.But glad you mentioned the m7b5 name. –  Tim Aug 31 at 15:32
    
thanks, that makes sense, it's from a mode of the harmonic minor, rather than directly from the minor itself? –  Tim Aug 31 at 17:08

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