Major 6th vs. minor 7th chords in high- and low-G tuning

I have a tenor ukulele in high-G tuning. When strumming along and a C chord is called for, I sometimes play C6 (all 4 open strings) instead to add a bit of colour. It seems to work well except in two cases:

1. A cadence to a tonic C chord (I don't play any jazz or blues where cadences to extended chords are common).

2. If C is a dominant chord, then there's sometimes a Bb melody note that clashes with the A in C6.

I also often play Em7 when Em is called for. It not only adds colour but is also normally a bit quicker for beginners like me to change to, depending on the previous chord. It also seems to work well, again with the exception of a cadence to a tonic Em chord.

C6 contains the same notes as Am7, and Em7 contains the same notes as G6, so you might think that playing Am7 and G6 when Am and G are called for, respectively, would work just as well. However, at least to my ears, they always sound wrong -- Am7 always sounds more like a type of C chord, and G6 always sounds more like a type of Em chord. I suspect that this is down to the voicing -- in high-G tuning, the C note is lower than the A note while the E note is lower than the G note.

So after all that, I'm finally getting to my question: Do other people perceive major 6th and minor 7th chords the same way, or is it just me? If it's not just me, is it the other way round for low-G players? In low-G tuning (and cuatro tuning), the A and G notes would both be in the bass, so would these two chords sound more like Am7 and G6 than C6 and Em7?

Welcome to UU. These kinds of questions come down to context - sometimes it works and sometimes it doesn't. You're right that voicing plays a big part. Melody and other instruments also affect what you can get away with on the uke. If it sounds good, it is good, and vice versa. There's little point in overthinking it.

ubulele said:

Check by playing 2213, which could be either F6 or Dm7—which do you naturally hear? Probably Dm7. But precede this chord with a single F note, and what happens to your natural interpretation? Now you probably hear the chord as F6.

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If I want to predispose the listener to one interpretation or the other (which I usually do), I may use one or both of these "forcing" techniques:

1. Precede the m7 with a minor triad on its same root, or precede or follow the 6 chord with a major triad or maj7 chord on the same root. It may suffice just to play the root itself before the chord, as in the Dm7/F6 exercise above.

2. Drop or raise the voicing to a different pitch range, supporting a drop or climb in root.

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Thanks for the tips! I'll be sure to try this out.

Well, a C and a C6 are not the same chord. Neither is an Em7 and a G the same chord. True, sometimes a different chord will sound better to you than the one called for in whatever song sheet you’re using. In fact, I routinely find wrong sounding chords published online, and change them to suit myself. Insofar as typical substitutions are concerned, I find that using a dominant 7 leading to the tonic is more satisfying than using a straight dominant chord in many situations. On the other hand, the 7th chord can be over used if one’s not careful. Another, related technique, is to use different inversions of the same chord to achieve an interesting harmony or base line. But in the end, it all just depends on what sounds best to you. There is no “wrong” choice if you like what you’re hearing.

Mike $ said:

If you are playing a song where the C is a dominant chord, then chances are you are playing in F which has a Bb note in the scale and in this case you wouldn't harmonize the C chord with an A note because as you can hear, they clash.

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Yes, they clash, and for this reason I would tend not to play a C chord as C6 if a Bb note is played or sung during the chord. However, as long as no Bb note appears during the chord, I don't think the fact that there's a Bb note in the key is a good reason not to play a C6 chord. By that logic, you wouldn't play F, Am or Dm chords in the key of F either.

Mike $ said:

You can substitute the Major 6 chords in the 1 and 4 chords, but I would use the Dominant 7 or 9 for the 5 chord.

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I agree that it's more common to use a dominant 7th or 9th for the V chord. That's because the V chord adds tension, and the tritone in a dominant 7th or 9th chord increases that tension. On the other hand, a major 6th chord just adds colour, not tension. However, I wouldn't say that you can never use a major 6th for the V chord. Here's a list of 193 songs that do just that:

https://www.hooktheory.com/trends#node=365&key=C

And if you consider melody notes that occur on strong beats to be part of the chord (which I generally do), then you could probably add a lot more songs to that list -- from "The Fields of Athenry" to "Mary had a Little Lamb".