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, and when used without any other qualifiers - exclusively used to denote a major seventh chord, even though that usage 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
Matt L.
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1Is there anything wrong with using "Cmaj7" instead of "CΔ7"? IIRC, Rocksmith uses "Cmaj7". – Cole Tobin Jan 08 '15 at 19:45
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3@ColeJohnson: No, there's absolutely nothing wrong with it. It's just one of several options. – Matt L. Jan 08 '15 at 20:40
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1CΔ9 and CmΔ9 are also common. Major 7th. major 9th. – Laurence Mar 05 '15 at 22:17
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1I respectfully disagree with the "exclusively used to denote a major seventh chord" statement. In modern days, it stands for "major seventh". For example, the music typesetting software I use, Lilypond, notates a minor triad with an added mayor seventh simply as "mΔ". – Alex Lopez May 04 '20 at 11:34
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1@AlexLopez: Thx for you comment, and I don't think we disagree. What I meant was that the triangle used alone without anything else always denotes a major 7th chord, even though I would discourage such a usage and would use Δ7 instead. In combination with a lowercase "m", it clearly denotes a minor triad with a major 7th. I'll edit my answer to clarify. – Matt L. May 04 '20 at 13:34
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Cheers, Matt :-) And by reading again my own words I just realised there's ambiguity in them too! Using words as opposed to notation, it seems difficult to distinguish between a major triad with an added major seventh and a triad (major or minor) with an added major seventh. – Alex Lopez May 04 '20 at 14:01
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@ColeTobin `maj7` is the far older way to denote a major seventh chord. – phoog Dec 12 '22 at 19:12
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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△
Some_Guy
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1You 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. – Sep 01 '18 at 05:06
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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 01 '18 at 05:25
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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 01 '18 at 05:27
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1@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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1@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. – Oct 27 '18 at 13:59
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@DavidBowling I've edited the answer, and avoided the term quality for the reason you've outlined. I haven't used function because I think that has its own problems, so I've simply said "major type" and illustrated what that means by example. – Some_Guy Oct 27 '18 at 22:48
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@DavidBowling, I'm merely stating how chords are viewed (and yes, chord terms are used, even potentially incorrectly) among the majority of working musicians, particularly in jazz, where these chords occur most frequently. – ScottM Oct 28 '18 at 14:14
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@ScottM -- Well, I am a jazz musician, and I have never heard any other serious musician say that a **C7** is not a major quality chord. Chord quality refers to the underlying triad. You are correct that jazz musicians tend to group chords into major, minor, and dominant (but here **sus** chords tend to fall under the dominant category, while augmented chords frequently fall under either major or dominant, showing that this is only a loose categorization). My original point was that delta chords _never_ mean dominant 7th chords. – Oct 28 '18 at 15:01
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