Constructing "add" (and other extended) chords confusion

Question

I've been struggling with this for a while.

• When building add chords like CaddX or dominant like CX do i always use major scale? Let's say i have C and Cm chords - shouldn't it be done accordingly major scale for calculating CaddX and minor for CmaddX?
• In another topic someone mentioned "add" chord only works when the additional note is higher then 7th. Are there no add2 chords then? Is that why C6 for example is so strange looking? (i'd expect it to be a dominant chord with added 6th since there's no "add", but it has no B♭)

Answer 1

If you want to use a scale, use Mixolydian.

But I prefer referencing a chord, a dominant thirteenth chord (from a major scale.)

The jazz chord name system doesn't reference any key or scale (the chords are never in major or Mixolydian, or whatever) so I think it's more logical to reference a default chord rather than scale.

So the reference chord, the dominant thirteenth, rooted on G, from a hypothetical C major scale, will contain tones: G B D F A C E G.

Use those tones and their intervals above the root, in simple and compound form, to get the default chord extensions and modifications.

Simple intervals are an octave or smaller, compound intervals are a simple interval plus an octave. Example, a sixth is simple (smaller than an octave), add an octave to a sixth to get the compound interval of a thirteenth. Simple and compound pairs: 2nd & 9th, 4th & 11th, 6th and 13th.

The seventh and larger intervals (9th, 11th, & 13th) are called extensions and just get added as a number. Any extension use implies the presence of all extensions down to the seventh. So a 13 chord implies the presence of the 7th, 9th, and 11th in the chord even though by convention some of those intervals are often omitted. (Usually the seventh is obligatory with higher extensions.)

When a simple interval is used, use sus or add like sus4 or add6. The label sus implies the sus tone is used instead of the chord's third. The label add means add the tone to a basic triad. So sus4 normally means the third isn't played, example Gsus4 is G C D. A Gadd6 is adding a sixth to the G triad, example G B D E.

Raise or lower any of the added numeric figures with a sharp to raise or flat to lower, except for the seventh which is raised with either maj or △ to mean a major seventh or dim7 for a diminished seventh.

...someone mentioned "add" chord only works when the additional note is higher then 7th. Are there no add2 chords then?

I think that is trying to say Gadd2 should really be written Gadd9, because it's more conventional to see a 2 as a sus like Gsus2, and because in practice people are not very picky about into which which octave the add2/add9 gets placed.

If you did allow both add2 and add9 to be used, then add2 should be a whole step above the root and the add9 should be a major ninth above the root. In both cases the third of the chord should be present. In the case of sus2 the third should not be present as it is "suspended" in the tone of the 2.

...Is that why C6 for example is so strange looking? (i'd expect it to be a dominant chord with added 6th...

If you follow the system, I think you will see that given tones C E G A Bb, the seventh implies a chord extended with compound intervals in which case the A is considered a thirteenth regardless of whether the A is actually a sixth or thirteenth above the root. It's theoretically a thirteenth.

Be mindful of potentially confusing figures, enharmonic naming, and more conventional labels. Example, G7b5 lowers the fifth of the chord from D to Db ...that means there is no D natural in the chord. Writing G7#4 would add a C# which is enharmonically equal to Db, but because that chord name doesn't alter the fifth it would mean G B C# D F where the D natural is included. The convention is to use G7b5 and the tones would be G B Db F with no D natural.

The system is a bit confusing, but once you get a handle on it, it packs a lot of chord information into a concise symbol.

Answer 2

The "m" only modifies the third of the chord and it does absolutely nothing to any other note of the chord. Chord symbols are used to describe chords, not scales. In Cm, "m" makes the third an Eb instead of E. When counting the steps, major scale based on the root note is assumed, except that "7" means minor seventh by default, and "maj7" is a major seventh. I think this is simply because the dominant seventh i.e. major chord with a minor seventh is so much more commonly used, so it's just practical that the shorter symbol means that. "maj9" means that the seventh is a maj7 and then there's an added ninth as well ... it might be a bit confusing, but it's just practical, it's not a grand design from a single mastermind. :)

"Add" can add a second just fine. Cadd2 is a commonly used chord symbol.

Chord symbols are more practical than theory-hygienic, and there's no international chord symbol standards committee whose approval anyone needs. :)

A power chord, i.e. a two-note chord without a third, is quite commonly written as "C5", even though a more systematic name would be "C omit 3".

The word "dominant" comes from a chord's role in functional harmony, as in, dominant-tonic motion. The stereotypical dominant chord is a major chord with a seventh, but you could use e.g. a G major without a seventh as a dominant chord for C, and it works just fine. But a G7 works a bit stronger in the dominant role than a plain G. Sometimes the word "dominant" is used to specify a chord type instead of role, meaning that there's a minor seventh, not a major seventh. Look at this Wikipedia page, you can see that the word dominant is used for both the chord type and the role/function. https://en.wikipedia.org/wiki/Dominant_(music)

In blues, a "dominant seventh" chord is used even as the tonic. That can even clear things up, because a "minor seventh chord" is understood as a "m7", where the "minor" refers to the third of the chord. A minor chord with a major seventh would be like "Cm maj7".

In my opinion, the best way to learn chord symbols and chord types is to encounter them in practical example situations, in songs. Trying to figure out and memorize the entire convoluted "system" feels hard. I'm glad I didn't have to learn it like that. :)

Answer 3

When part of a chord symbol, 6ths (13ths) are always assumed as major, just as sevenths are assumed to be minor. I think a good general rule is that all extensions come from the mixolydian scale on the root if no other qualifying symbols are given.

C6 has an A♮, so does Cm6. X6, for whatever reason, is always X triad with an added major sixth. Not a dominant chord, but it can be used as one.

If you want any different extension, you'll need to write in something like "m", "maj", "♭", or "♯" in order to imply those extensions. As an example, [C E♭ G A] would be Cm6/9, but [C E♭ G A♭] would be Cmadd♭6.