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Recently I found that Cdim7 chord and Cm7b5 has same set of notes in their chords but they have different names. So, are they same ?

In general, do we find chords that have the same set of notes but have more than one name?

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Cdim7 and Cm7♭5 are not the same chord. Both are built from diminished triads, but a Cdim7 has a diminished 7th (C E♭ G♭ B𝄫, sometimes incorrectly spelled C E♭ G♭ A for convenience), while a Cm7♭5 has a minor 7th: (C E♭ G♭ B♭).

The Cm7♭5 chord does have another name, though. It is often called a half-diminished C chord, or C. As for why there are two names for this chord, sometimes it feels like less information to process when you think about this as a distinct type of chord (half-diminished, with one symbol: ) instead of as an altered seventh chord (minor seven flat five, with four symbols: m7♭5). Half-diminished chords show up in minor keys a lot; for example, in ii - V - i progressions. They don't appear much in major ii - V - I progressions. It can be helpful in keeping such a minor progression straight to think ii - V7 - i instead of ii7♭5 - V7 - i, compared with ii7 - V7 - I for a major progression.

To make matters more confusing, for every half-diminished chord there is a minor 6th chord with the same spelling! So a C (or Cm7♭5, if you like) has the same notes as an E♭m6. Which name is chosen for this chord will depend on the context in which it appears. Context is important for naming any chord.

  • As an additional caveat, in "classical" music, chords are often called what they are (C half-diminished, Bb neo-whatever), whereas in jazz music, chords are named by how you create them (Cmin7b5, G7add#4, etc.). – John Doe Apr 16 at 16:44
  • @JohnDoe -- not sure I follow. There are a lot of ways to name chords in both "styles", to be sure; but both "classical" and "jazz" are very broad categories. – David Bowling Apr 16 at 23:42
  • @David Bowling we could make things even more confusing by stating every dim7 has also an enharmonic dim6. e.g. Cdim7(1-b3-b5-bb7), Cdim6 (1-b3-b5-6) or even Cmin6b5 (1-b3-b5-6). In theory, we could go beyond absurdity with this and call it also a CMaj6(b5b3). – dfhwze May 6 at 17:33
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As @DavidBowling explained, Cdim7 and Cm7b5 are not the same chord. But the question remains: Why do we find chords that appear to be same, yet are referred to with different names.

On that question, here is the answer: There is no standard naming convention for chords that everyone follows, outside of simple triads and Dominant 7th chords. (Many have tried and failed to establish some sort of standard...) You can look at three music books and find three different ways of naming certain chords.

Often in the introduction to a book you will find a section explaining that particular author's naming convention and method of designating chords used in the book, although they don't need to explain their naming convention for notes and the common scales - because there is no clearly agreed upon standard for chords.

This is because in modern music, working musicians communicate a great deal of their music through chord names and progressions as opposed to reading from scores, and to do so they will use whatever chord names are convenient at the time and understood by their compatriots. The determining factors can vary greatly depending on the genre and the musicians involved. The goal is simply to communicate the musical idea as simply and clearly as they are able to, without regard to formal terminology.

In modern music, chords are also very fluid - guitarists and pianists in particular often come up with new sorts of extended, modified or partial chords - and how they are named is just as fluid. Working musicians do not take out their copy of Slonimsky's Thesaurus Of Scales And Melodic Patterns to help them determine the precise technical name for every new extension or alteration they come up with. As long as they can communicate their musical idea, that's enough.

Moreover, many musicians have little knowledge of formal theory and terminology and simply name chords based on their own understanding of how they are built, played and function.

We can rightfully call our naming of chords "a living language". We find that, as David has mentioned, a Minor 7b5 chord is often simply called a half diminished chord - much easier to yell that out in the middle of a jam session, and also such names as the Hendrix Chord for a Dominant 7♯9 chord, and a Power Chord, which refers to a chord often found in rock music, comprised of a root and a 5th. (Just to name a few of the commonly encountered informal but practical names for chords.)

These names arise and persist in our vernacular musical vocabulary simply because they are easy to remember and communicate to others, which is the primary consideration for musicians working outside of formal classical settings.


New names and ways of referring to different chords are constantly surfacing, as times and musical styles change, so it's hard to ask why the same chord may have more than one (even several) names. It usually just depends on what you read or who you talk to.

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As others have said, your examples are not the same but there are simpler examples of chords with multiple names.

C E G A has the most obvious name of C6 but its third inversion is A C E G which has the most obvious name Am7. You may say that C E G A and A C E G are not the same chords so the different names are not a problem but consider other inversions.

C E G A - C6 root position or Am7 1st inversion?

E G A C - C6 1st inversion or Am7 2nd inversion?

G A C E - C6 2nd inversion or Am7 3rd inversion?

A C E G - C6 3rd inversion or Am7 root position?

When I first noticed this as a child, I wondered whether it sounded major or minor. The answer, of course, is: it depends. In one context it might sound major and another minor.

So, which is it? Things don't necessarily have unique names. Even in a subject as precise and rigorous as mathematics, terminology varies from author to author or paper to paper. Or in chemistry, which is not only rigorous but has a controlling body (IUPAC), chemical names are not always unique. It is just too hard to achieve. Priority is given to ensuring that a name can only mean one substance. Having multiple names for one compound is accepted. We can take the same attitude to chords. Life is easier if when I say a chord name, you know what I mean. It is less serious that there may be other names. No worse than C# and Db indicating the same key on the piano.

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