Diatonic seventh chords

Finding dominant sevenths from the triad

On the mandolin, my “guerrilla” learning style has thus far been focused on constructing four-string chords, both for a fuller voicing and (let’s be honest) to allow the right hand to cruise sloppily.

Structurally, it’s been about regular permutations deliberately limited to moveable forms. So, for triads, I carried over what I’d learned on the Guitar Craft-tuned guitar, from a California Guitar Trio exercise: one form per inversion, root, first (third in bass), and second (fifth in bass), with the other strings advancing diatonically up the neck as well. So, for A major, the three inversions with A, C#, and E in the bass would be:

This proved to be so helpful in my learning that I sweated out the same thing for the diatonic sevenths…again, one form per possible inversion, advancing up the neck, moveable forms. Translating directly from the guitar, for Amaj7 as an example, the forms for A, C#, E, and G# in bass, are:

The really geeky may notice that in first inversion I altered the triad, flatting the root to the major seventh; this allowed me to use the root on the top string, keep all four component notes in the chord, and have each form truly advance the bass and treble strings up the neck each time. It was an arbitrary choice, but it helped me construct a box that really helped me to “see” the chord forms advancing up the neck.

On the mandolin, I ran into another problem: some of these forms are simply too tight to work well on the smaller instrument. (By contrast, stretches like the second-inversion maj7 voicing are very workable on the mandolin while being a real workout on the guitar.) I realized that I would eventually need to find other convenient voicings for the mando.

Somewhere in there I ran across Jethro Burns’ outstanding book, which advocates the concept of the three-string chord (even for chords with more than three tones) on the basis that it can be altered more easily than a four-string chord. True, but that introduces an unintended problem for the beginner: how can you understand what chord tones you can omit, before you’ve got a good grip on where the possibles are? I ignored the three-string approach at the time, staying with my fours and developing some confidence (this was a good decision, at least for me), but how funny what comes back in due time. With a good grounding in where all those notes actually are, and watching Mike Marshall articulate the same advantage of alteration in one of his excellent video resources, I actually started to “get it”. In working with a couple of David Grisman tunes, the three-string chord really started to show its value, and with that came another revelation: the three-string chord is much, much easier on the tightest fingerings.

Great. So I’ve started to explore the three-string chord concept, with an eye to building a library of chords for my own use. And, quickly enough, the “omit tones” problem rears its head, to wit: how does one intuitively know where to find a three-string chord that omits the root?

As with many things I’ve learned about music so far, at least one example turned out to be a “duh” moment. I was playing around with the four suggested inversions of a three-string dominant seventh, as noted by Burns. Going up the neck, this is A7 with G (7th), A (root), C# (3rd), and E (5th) on top:

Now you may notice that the note A only appears once in those four chords, as the top note of the seventh-in-bass inversion. So: how the heck do I quickly find an A7 that doesn’t even have an A in it?

I found myself noodling a bit on this, and stumbled on creating the seventh out of each triad inversion, by flatting the root note by a whole tone. Whoa, there they are!

Then, what really bent me is that suddenly I also recognized that these root-omitted dominant seventh chords are enharmonically the same as the diminished triad build on the chord’s third–in each inversion. That is, A7 with no root (C#-E-G) is also a C# diminished triad. This makes complete sense, of course, since a dominant seventh is nothing more than two minor thirds stacked on top of a major third, and if you omit the major third, what you’re left with is two minor thirds–or a diminished fifth. Quo erat duhmonstrandus. (Okay, maybe it takes a geek to appreciate that, but sue me, I love this stuff.)

Excepting the form with root on top, then, which kind of lives “in between” the third inversion and the first, I can now find any dominant seventh by finding the appropriate triad and altering it. This three-string chord thing may have some value yet!

Finding sevenths from the triad

Continuing this theme of using the three-string triad as a template to alter into other chords, I’m starting to see forms I’d never thought of before. I was noodling around for Sabre this evening, trying to think on three-string triads, and wound up making another accidental “duh” discovery.

For those of you who can appreciate stream-of-consciousness thinking, here’s how the sequence went: I started by revisiting the first suggested “alter the first-inversion triad to get a dominant seventh” suggestion, on G major. On the mandolin and other fifths tunings, that looks like this:

Well, what about going the other way? If we can take that root down a whole step to get G7, what about going up a whole step to get the ninth? It’s probably fudging the point a bit from a Juilliard/Berklee point of view, but that could probably serve as both Gadd9 and as Gmaj9, depending on what notes others are holding down.

And that’s got to be so much easier to think of doing, at speed, in an improvisational context. If we consider the mandolin (or the Guitar Craft guitar, for that matter) as but one voice among other instruments, this would promise to be a very effective way of adding color notes with less risk of bumping into others’ territory.

From here, it can start to get pretty fast and furious. On that first-inversion triad (third in bass), I just started permuting:

That rather neatly covers those*; then, you could start walking the fifth around as well (for this diagram, read down, not across, to see the permutations):

This could get out of hand in a hurry, but on the other hand (and with apologies to Frank Zappa), great googlymoogly! And that is just the first-inversion triad…I’ll try my hand at root-inversion and second-inversion next time, and holy cow, then there’s ninths.

I suspect that there are a couple of goals with going further down this approach:

  • The real goal here is not just to build a library of chords to memorize, but to become competent at finding a triad and altering it on the spot (and herein is where the value of reducing from four strings to three becomes obvious, saving what must be a fairly staggering amount of complexity)
  • With the enharmonic equivalents starting to pop off the page (with just three strings to keep track of, it’s much easier, isn’t it?), it seems that using this approach will also underscore the need to better understand polychords, both from the standpoint of deliberate construction of polychords by multiple members of the group playing simple chords, and also from the standpoint of reduction of polychords into smaller constituent pieces that a player can grab onto either at speed, or to allow a humane fingering. (I think I’m going to have to chew on that one for a while.)
  • One nice thing about using three strings instead of four is that it does leave the player more room to wander about the registers, in effect “playing his harmony with more melody”. I suppose that a complete player would want both full voicings and the three-string variants at his disposal, but the potential for improvisation here is pretty huge.

Note to self: don’t sit down to write the bit on ninths until you have a lot of time. 🙂

Training with diatonic sevenths

Let’s face it: training yourself to ingrain a chord library is a bit of a chore. A chore that pays worthwhile dividends, to be sure, but a chore nonetheless. Today, somewhat out of the blue, I realized that I have to add another item to the practice regimen. It came out of trying to re-familiarize myself with diatonic sevenths from the Western major scale on the Guitar Craft tuning’s top four strings. I’ve got a lot less time in these shapes than I do with the shapes of all-fifth-intervals, and that’s probably what brought this thought out: I need this skill now, because my constraint of the NST intervals on the banjo means that I don’t have four strings in fifths to lean back on. This is exactly what I was hoping to force myself to do here.

My basic chord library–what I try to train myself in as a basic competence–follows a few key constraints:

  • Closed shapes only, available to any key.
  • One shape per chord inversion (so, if I want to master Cmaj7, I construct four shapes, so that I can put any desired note in that chord–C, E, G, or B–in the bass or in the treble position)
  • Inner chord tones may be swapped around if fingerings become superhuman (some of ’em are pretty tough!)
  • All chord tones represented if at all possible (and in all but a couple of cases, it is!)
  • Use of a four-string group to cover the chord (three-string chords introduce the structural complexity of “which tone to omit?” which I think will be a useful thing to address after I’ve cemented the basics)

Yep, they’re arbitrary constraints, but building a library this way has helped me immensely with comfort with chords, and it’s given me a vehicle to alter them methodically. I can recommend it with enthusiasm.

So! When practicing these inversions, I like to walk up the scale playing the diatonic chords (that is, Cmaj7 – Dm7 – Em7 – Fmaj7 – G7 – Am7 – Bm7b5) according to these rules:

  • First: Play each inversion of a chord before moving to the next chord. That is, play Cmaj7/C, Cmaj7/E, Cmaj7/G, and Cmaj7/B before moving to the Dm7. I like doing it both starting with the root inversion of each chord, and then starting with whatever inversion is closest to the nut. This builds a sense of how to move from one inversion to another within the same chord, at different spots on the neck (when I use keys other than C major).
  • Second: Play the I chord of the key (whatever inversion you choose to start with), then the closest II chord, then the closest III chord, etc. When moving from VII to the root, play the next highest I chord inversion. Again, I like to do it both starting on the root inversion of the I chord, and then again with the lowest available inversion of the I chord. This exercise gives you a sense of the chords closest to your original hand position, and it also teaches you how the different inversions interrelate to each other over the entire fingerboard. This is really eye-opening, to watch yourself go through four passes through the key, playing seven chords at a time, and only occasionally needing to move your hand position more than a couple of frets at a time.

I started to do this second exercise today, in a different key than C, and realized that I froze up because I had started to internalize the key of C, rather than the abstract shapes determined from inversion and scale tone. Which inversion was I looking for again? Well, drat. More work to do.

So: I am now going to add to that this exercise:

  • Third: Play the chords of the scale, ascending, all in the same inversion. This should accomplish two things: first, it should cement how the chords alter the basic shape common to the chord inversion (i.e., which tone goes flat to turn a M3 into a m3); second, it should help you to understand where your next chord should be, ascending or descending, in the same inversion…this may help to develop a sense of where the other chords overlap (in theory, one should always be able to play the chord a diatonic third up in almost exactly the same hand position as the chord you’re on…so you can develop a cadence: I chord in root inversion, shift up a whole tone to II chord in root inversion, back down a whole tone to III chord in a different inversion, then up a whole tone to the IV chord in that same inversion, back down for the V chord, back up for the VI chord, back down for the VII chord and then up to the next available I chord…). It’s an oversimplification, but only barely. It works in all but a couple of special cases such as “do I alter the chord in order to play it at the nut rather than at the octave, because one of the chord tones would be ‘just below’ the nut?”

Time to put that into practice. I expect it to be a great skill-builder, and will report back here with a little work.

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* How about the bender of the enharmonic equivalents, as well? That three-string Gmaj7 is also known as Bm, which is a standard third-up substitution…also check out Bb augmented aka Gm/maj7, Bb major aka Gm7 (diatonic third up and relative major).

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