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Why are major seventh chords called delta chords and written with a delta symbol, like CΔ7 or CΔ? Do engravers consistently use Δ to mean a seventh chord (such that Δ7 is redundant) or do some use Δ simply to mean major?

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The triangle symbol Δ originally meant "triad" (meaning major triad) [1]. However, nowadays it is - at least to my knowledge - exclusively used to denote a major seventh chord, even though it is a bit sloppy. I recommend you use Δ7 for denoting a major seventh chord. This will avoid any possible confusion, and it is also the symbol I come across most often.

[1] The Chord Scale Theory & Jazz Harmony, B. Nettles and R. Graf

  • Is there anything wrong with using "Cmaj7" instead of "CΔ7"? IIRC, Rocksmith uses "Cmaj7". – Cole Johnson Jan 8 '15 at 19:45
  • @ColeJohnson: No, there's absolutely nothing wrong with it. It's just one of several options. – Matt L. Jan 8 '15 at 20:40
  • CΔ9 and CmΔ9 are also common. Major 7th. major 9th. – Laurence Payne Mar 5 '15 at 22:17
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△ without further qualifications in most contexts means "some type of major chord".

The point of these chord charts is to indicate to the player the most important information about the harmony of a given song. Usually, where the symbol "△" is used, we're talking about a jazz context. In this context, which specific major chord to use is left to the tastes of the performer, and so when one sees C△ in a lead sheet it might be rendered variously as C△7, C△9, C6/9 etc.

In the same way we often don't feel the need to tell the player which inversion to use, in jazz we often don't feel the need to tell the player which specific type of major chord to use.

Similarly, we often don't specific inversions; take for example a dominant chord (instead of a major chord), most of the time we see G7 any inversion of will do, but sometimes we really want the F at the bottom, in which case one would write G/F.

The same goes for major chords; if it's really important then be specific (e.g. C△9/G), and if it isn't then let the player decide what specific chord and inversion to use and just write C△

  • You can maybe get away with "...in most contexts means major quality chord," but I have never seen an instance of a C△ that could be a C7, which is a major quality chord. – David Bowling Sep 1 '18 at 5:06
  • perhaps quality is the wrong word, I very nearly just said "flavour". A C7, C9, C7♭9 etc. are all a "dominant" chords and "Δ" is a "major flavour chord", for want of a better term. I don't know what exact term to use, but basically anything that "functions" as a major chord. I don't know if dominant chords count as major quality, if they do then that's the wrong word to use. – Some_Guy Sep 1 '18 at 5:25
  • The main point is that C△ does not necessarily mean C△7 as the accepted answer suggests. In fact, there are many cases when another major chord would be preferable, or even just a triad sometimes! – Some_Guy Sep 1 '18 at 5:27
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    @DavidBowling, C7 is not considered a "major quality chord" among most serious musicians, particularly jazz musicians. They consider there to be 3 types of chords: major, minor, and dominant. Thus C7 would be a dominant quality chord, not a major quality chord. – ScottM Oct 26 '18 at 18:33
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    @ScottM -- You are confusing chord quality with chord function. Chord quality refers to the underlying triad and can be major, minor, augmented, or diminished, but not dominant. Chord function can be dominant, and a 7th is not required for a chord to be dominant. Standard chord nomenclature names: root, triad quality, highest degree of the structure when built in 3rds above the root, finally alterations or added pitches. This is how Nettles and Graf describe chord symbols. – David Bowling Oct 27 '18 at 13:59

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