Why does a minor sixth chord contain a major 6th interval?

Question

This is something that has always puzzled me. Perhaps I am going about this the wrong way but when I build chords I always build them based on the scale that corresponds to the quality of the chord. For example...

CMaj7 = C-E-G-B ; Same notes that are in the CMaj Scale

Cmin7 = C-E♭-G-B♭ ; Same notes that are in the Cmin Scale

C7 = C-E-G-B♭ ; Same notes that are in the Cmix scale

CM6 = C-E-G-A ; Same notes that are in the CMaj scale

but....

Cm6 = C-E♭-G-A ; Same notes as the c min scale except for A (Should be A♭)

Why does Cm6 have a major 6th interval and why is it not built on the minor scale?

Answer 1

The chord C-Eb-G-A has a major sixth in it because it provides the harmonic tension characteristic of this chord's sound, namely by virtue of the augmented fourth between Eb and A. An Ab would not produce this same tension. The chord is called "minor" because of the quality of the triad C-Eb-G. The word "minor" in this case has nothing to do with the quality of the sixth. If you like you can think of it as a Cmin add6 chord. In any event, try not to get too caught up in the name, because as this wikipedia article explains, there are several different names for this chord.

Concerning the scale the chord is built on, I would argue that it's not the melodic minor scale because that would imply that the sixth would have to rise through the seventh and up to the tonic. In practice, this added note is generally used for the harmonic interest it adds, not any melodic directionality. So if this chord sounds like a tonic chord in a piece, a more appropriate scale origin would be the:

C Dorian scale:

    C  D  Eb  F  G  A  Bb  C

Note that this chord quality is often used for the subdominant in minor keys. So this same chord, C-Eb-G-A could easily serve as the subdominant in G minor, and in this case it would be derived from the G natural minor scale.

Answer 2

Chord symbols are not intended to be related to a “key”. The symbols are an attempt to describe the chord itself with no indication of value in relation to the key in which it is performed.

A minor 6th chord uses a major 6th interval because the “minor” word applies only to the 3rd in the chord (the difference between whether it is a minor or major triad), and the 6th is a given that it is a major 6th. The same idea is apparent with a dominant 7th chord.

A chord with the notes: (C E G B flat) is a dominant 7th chord, or it can be called a (C major flat 7) chord, but requires much more space and energy to describe it. The chord symbol system is used as a sort of shorthand for harmonization and therefore terms are used sparingly. So, the symbol (C 7th) is used to indicate a (C E G B flat) chord because this dominant 7th chord is the most common 7th chord used historically, and the C major seventh chord is written in the symbol (C maj 7th) to indicate that the major seventh interval is used instead of the more common flat or dominant seven.

With the sixth chord, we have the same idea, but it is reversed, the major interval is much more used historically than the minor sixth interval, so the longer description lies with the lessor used version of the sixth chord. (C minor 6th) or (Cm6) is (C - E flat – G – A) where the “minor” applies only to the third interval. The (C minor-minor 6th) or (Cm m6th)or (Cm b6th) would be the notes C - E flat - G - A flat. Where the small b should be a flat sign.

Answer 3

The Cm6 chord has a major 6th interval in it simply because the "minor" refers only to the second note; it informs us that the second note is a minor third.

The notation and terminology is such that "minor chord" doesn't simply mean "everything that has a major/minor designation must be minor".

Unfortunately, it is not consistent, either. Or, fortunately, depending on the point of view. It turns out that things are the way they are because compactness of common forms beats consistency.

In this case, the Cm6 means the "Cm" triad, plus a 6th. If there is just an "m", it makes the triad minor.

The confusing thing, perhaps, is that the "default flavor" for a 6th is major, but for a 7th it is minor.

That is to say, if nothing else is written other than the digit 6, it's a major 6th. A minor chord with a minor 6th would be written "Cmm6": a Cm plus a m6.

The opposite default applies to the 7th degree. A 7 by itself is minor, rather than major.

What is worse, the letter M doesn't apply to the triad, but to the 7th degree. Thus C7 means the C triad (i.e. major), with a minor 7th.

There is a certain logic to it nevertheless, which is why you don't really have to think about this. The default triad is major, so you write C for the C major triad, and use an explicit m for the minor triad only. This means that the upper case M never refers to the triad, and the lower case m always does. Given that convention for triads, the rest of it follows. The letter m is occupied by denoting the triad, but the letter M is free, having no use. So the convention is that CM7 denotes the major 7th, and the absence of M, C7, denotes the dominant. The opposite convention wouldn't work that well. If C7 denoted the major 7th chord rather than the dominant, we would have to write CMm7 for the dominant, which is clumsy for such a frequently needed chord (already verbose without any additional voices like 9ths, 11ths and so on, and alterations).

The 6th interval has no such issue: we make it default to major, and that works because it appears often, over either a major or minor triad. If an explicit M had to be written to get a major 6th, then the nice notations like Am6 and C6 would become AmM6 and CM6, or perhaps CMM6. Am6 would still exist, and would denote the much more rare Amm6 chord.

In any case, all the cases not covered by common usage can just use two m's to spell out which triad and which 6th or 7th. The notation being the way it is lends a terse expression to all the chords that come up in the musical traditions to which that notation is tied.

Answer 4

Just because the chord is named C, doesn't mean that it only belongs to some C scale (either major or minor or whatever); it could belong to other scales as well.

This would be the case if it were the melodic minor scale. In Jazz, the C melodic minor scale is: C,D,Eb,F,G,A,B,C -- which is just like the C major scale with a flatted third.

Also, this chord could belong to another scale as well; to the Bb major scale ( or the G natural minor scale). Both of these scales have Eb, but A natural, thus resulting to the C-Eb-G-A chord you mentioned.

Answer 5

which minor mode are you speaking of? There are 3 of these:

• natural minor (minor 6, minor 7) aka Aeolien
• harmonic minor (minor 6, major 7)
• melodic minor (major 6 and 7).

The "m6" chord is related to melodic minor mode.

The "mM7" chord can be related to either the harmonic minor or the melodic minor mode.

The "m7" chord can be related to the natural minor scale or the dorian scale (minor 3rd, major 6th, minor 7th) or the phrygian scale (minor 2nd, 3rd, 6th and 7th), although you will generally have more indications by the author if he wants something specific. By default "m7" means dorian, and you will have "mb9b6" for phrygian and and "mb6" for natural minor.

These are only the most common modes. See The Scale Syllabus for more possible modes.

Answer 6

The fact that a m6 chord is based on the melodic minor scale has already been pointed out in other answers. I'd like to add that a minor triad with a minor sixth is just an inversion of a major seventh chord, so it wouldn't add anything new. E.g., a C minor triad with a minor sixth would have the notes

C Eb G Ab

which is just the first inversion of an Ab major seven chord:

Ab C Eb G

Answer 7

I think you are approaching this the wrong way around. These jazz chords are seventh chords build around the idea of having certain triads and adding colour to there sound by adding a certain type of seventh to them.

Only the dominant seventh is a type of chord that you would use in traditional harmony. The other types of chord are just interesting variations.

These seventh chords are often more interested in what type of seventh the chord has that just the mere nature of the third.

Sixth chords are different though. That sixth has a distinctly dissonant quality. This means that sixth chords are often just a type of passing chord which leads in a interesting way to other chords.

This is probably why the nature of the sixth is not reflected in the notation but rather just the indication of what type of triads it is. This may very well be more useful to a jazz player when deciding what chords to follow the sixth chord up with.

Answer 8

I'm with you on the CMaj7 and the Cmin7. After that, I start to get a little queasy.

In general, you should be building chords based on the scale of the key you are in. So, think of your C7 as being the dominant in the key of F (or f minor).

Things make better send to most of us mere mortals if we learn them in a specific tonal context.

Answer 9

It does simply because it is defined to be with those intervals. Instead of worrying about it, consider that it is a "magic" chord - that is what this one is - and enjoy the sound. Play the C Eb G A chord with any one of the constituent notes moved to the bass, e.g. Eb C G A (bottom note first) then think, what next? You will find that there are an enormous number of chords, not necessarily in the key of C minor, which sound good and natural after it. Chords don't mean much unless leading somewhere. In the example Eb C G A try following this with another made by moving any 2 of the notes by a semitone - so we might get D C F# A, and instant D7 chord asking please to resolve to G major: G D G B. There are thousands of possibilities, it's indeed useful chord.

Answer 10

Cm6 is as C, Eb, G, A as an M6 instead of m6. Cb6 Contains C, E, G, Ab as an m6 as an Mb6. Cmb6 Contains C, Eb, G, Ab.

Answer 11

The simplest way to comprehend this is the word 'Major' is only linked to Maj7 chords. This means, I only pronounce the word 'Major' just for 'Maj7' chords. For example, if I called a C chord simply a 'C'(or dominant C) and not 'C Major'. Then only I can comprehend and differentiate between:-

C7 Chord: 1-3-5-b7

CMaj7 Chord: 1-3-5-7

Therefore, there is only a C6(C major w /the 6th note) and Cmin6(a C minor w/the 6th note). NO 'C Major6' or 'C Maj6'!!

Why does a Cmin6 have a Maj6 interval and not a min6?

Because the minor interval itself is derived from a major's. Cmin intervals: 1=C, b3=Eb, 5=G. If Cmin6 is built on its own minor scales, then Cmin7 C, Eb, G, A instead of C, Eb, G and Bb. Because according to its minor scale , the 7th interval is already Bb.