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  1. I have seen/ heard people say that you only write a 6 when there are no other upper extensions used (meaning no inclusion of 7 and above).

  2. I have also heard people say that you only write a 6 when there is no 7th in the chord.

So, if we take E/G as an example, I would call this a G- flat 6 (add) flat 9. But I have seen this chord referred to as a 'G13 flat 9 sound'- ('sound' not 'chord'- as it is incomplete, with no 7th). This second labelling is more in keeping with the first view (1). 6/9 chord labelings seem to be more in accordance with the second view (2).

So, is there actually a definitive rule behind whether something is a 6 or a 13?

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If there is a seventh then it's a 13th, otherwise a 6th.
A chord with a sixth and a ninth but no seventh is common.
Chords like E/G are probably better written as a slash chord rather than trying to force them into the standard naming scheme, particulary since there's not only no seventh, there's also no fifth.

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A 6/9 chord is just what it is - including M6 and M9. As C6/9 - C E G A D. A fine chord in its own right. The 6th is actually the 6th, and the 9th is actually the 9th.

Once the numbers go beyond 7, they are the actual notes involved. So, when that note is deemed the 13th, the 7, 9, 11 may well be included within the chord. It's not unusual that some notes are omitted, but the 7th must be there. At that stage, the 13th is 13th, rather than 6th.

Otherwise the chord will be a simple 6th.

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Let's explain using G13 as example.

We start with the basic G major triad: G/B/D and the than we stack thirds on top of it. So G7 would be G/B/D/F, G9=G/B/D/F/A, G11=G/B/D/F/A/C, and finally G13=G/B/D/F/A/C/E

At this point the chord includes all notes in the C major scale, i.e. all the white keys on the keyboard. You can simply take a 2x4 and press down as many white keys as you can. If someone asks "what the heck are you playing?" you can answer "Why, dear sir or madam, that is a G13 chord" and you'd be theoretically correct.

In practice you will still get kicked out of the band, since it sounds terrible. It also poses a problem for guitar players: there are seven notes in the chord and you have only six string.

Obviously you don't play all the notes. Most chords have a key "tension" interval that creates the character of the chord. Make sure you capture this. You also want to include the third just to make sure you can distinguish between a major and a minor key.

For the G13 the tension interval is 13 vs 7, i.e. E vs F. You also want the E on top, hence you write it as a 13 and NOT as a 6. For grins you can try playing the F on top as well: You ears will NOT be pleased! The other chord notes are optional and can either add flavor or clutter things up depending on what else is happening.

So in this example your minimum set a good choice of notes for a G13 would be G B F E and that's probably what the person who scribbled G13 on the chart intended. If you have a competent bass instrument in the band, you can also drop the root and simplify further.

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  • thanks for this great answer Hilmar. One thing I'd still ask: if you DID put that 6th interval BELOW the 7, would the chord then become a 6 ? Or would it still be written as 13, even though it is actually at a lower pitch than the 7? I'd imagine if it contains the 7, youd still call it 13?
    – EdB123
    Feb 28 at 15:20
  • I guess you could write it as a 6/7 or 6/15 but it would be fairly unusual. It's not very pretty
    – Hilmar
    Feb 28 at 20:40

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