We previously discussed sliding 6th chords. A Maj 6th chord is built with Root, Maj.3rd, 5th, and 6th notes of the related major scale. We wanted more of a triad sound, so we will discard the 5th of the chord. For an E6 chord, we would have E, G#, and C#, having discarded the B note.
The E6 chord can slide down two frets to D6. If the bass note remains E, then we have the notes F#, B, and D. These can be considered the 9th, 5th, and lowered 7th note of the E7 chord.
However, let’s talk about the “other” 6th in this scenario: the 6th interval. When we invert a 3rd interval from a chord, we put the bottom note of this interval on the top.
When we think of the Major 3rd from E up to G#, we may raise the E an octave and consider the new interval, G# up to E, to be a 6th interval. In relation to the E6 chord, we can discard the 6th of the chord(C#)and we’re left with only the Maj.3rd of the chord and the root of the chord. We’re outlining the EMaj chord, or E. We can also invert minor 3rd intervals into 6th intervals. Let’s move our 6th interval up to the next diatonic notes in the key of A Major. That means the A-to-F# 6th interval. There are only two 6th intervals available, the Maj.6th and the Min.6th. We can harmonize the A Major scale with them:
We’re harmonizing the A Major scale because we’re talking about the E7 chord, and this chord is diatonic to the key of A Major. These 6th intervals will all sound good over an E7 vamp. This scale may be considered the E Mixolydian mode of the A Major scale. We’ve harmonized the E Mixolydian scale, which could also be considered the E7 scale. It’s the diatonic scale for E7, although there are other scales which can stem from the E7 tonality, so it’s best to be more specific than “E7 scale”, and call it by the actual name, E Mixolydian. Modes of the major scale will be covered more in depth at a later date.
In particular, the 6ths with the E note on the top will sound strongest over this E7 chord, which are the first and last intervals in the above example. Notice that sliding between the “Bm” and “C#m” voicings will sound good over the E7 chord, just like the D6 and E6 chords work over the E7 chord previously. Additionally, notice that the “G#m” voicing contains the 3rd and 5th of the E7 chord (G# and B, respectively). The “F#m” and “A” voicings will sound better as passing notes, mainly because scale tone 4 clashes with the 3rd of the chord.
So, for each triad, we have two sets of 3rds: root ascending to 3rd and 3rd ascending to 5th. That’s also to say that there are two sets of 6ths, as we invert the 3rd to a 6th. 3rd ascending to root, and 5th ascending to 3rd.
For a 7th chord, we have 3 sets of 3rds, which can be inverted to 6ths: root ascending to 3rd (inverted: 3rd ascending to root), 3rd ascending to 5th (inverted: 5th ascending to 3rd), and 5th ascending to 7th (inverted: 7th ascending to 5th). We could also add the 7th ascending to 9th (inverted: 9th ascending to 7th). Work these through different keys and alternating through string set 1 & 3, as well as 2 & 4. Also change octaves where desired/necessary.
Use your ears and have fun!