Not only can we not play full-fledged triadic extended chords on the guitar, but we can’t always play the notes of a special-effects chord in triadic order. (We can always do that on a piano.) So guitarists jumble the notes around the fretboard until they find a combination they can play and call
that the “D♭13”. If they can’t manage that, they drop one of the notes and try again. This is why guitar chord books will show two different chords in different positions under the same name with nary a word of explanation.
These variations are called “voicings” of the chord. Because that sounds like they meant it.
What does it mean to say you’re playing B♭minor 7♯9 on the guitar, if there are three ways of doing it and each of them has a different set of notes in a different sequence (from the sixth to the first string) and each voicing may be a third or more higher than the next?
It means two things: first that the triadic naming convention rapidly becomes unwieldy above sevenths; second, that
you’re hip to the tricks of the trade you have the musical taste a) not to make a fuss about the ambiguities, and b) to know which of the “voicing” of an extended chord fits which situations.
It’s even worse than that. Many guitar chords are “voiced” across all six strings. So we can strum an accompaniment easily.
The strummer’s F-major chord in the first position is F-C-F-A-C-F. An F-major triad is F-A-C - in any key. The six-string chord has the 6-4 inversion (C-F-A), the fifth (F-A-C), and the sixth inversion (A-C-F). Two are major fifths (C-F-A, F-A-C) and a minor fifth (A-C-F). All in one chord. It’s triadic sludge. So are all the other cowboy chords (so-called because they can be strummed across all six strings in the first position).
Classical guitarists don’t strum, so this mess does not happen in classical music.
So does this mean (non-classical) guitarists are doing something wrong, or does it mean that conventional triadic harmony is not the best way of understanding what kind of harmonic contributions the guitar can make?
I would say the latter.
There’s a story about Joni Mitchell working with Tom Scott. She’s playing piano and Scott - a fearsome jazz session musician - is in the recording booth. Joni plays one of those “Joni Mitchell” chords, and Scott hits the mic and asks “Is that an A-flat 4th diminished 6th” (or some other such). Joni looks at him, then at her fingers on the keys, and then back again.
“Tom. Ignorance is bliss.”
I’d suggest that guitarist-harmony / chords is more bliss than book. The better songwriters find their “odd chords” by experiment as much as theory. The theorists then rave about so-and-so’s use of a minor ninth sus-2 (or whatever) as if so-and-so thought about it, when in fact, it’s a chord that results when playing something fairly ordinary and moving one finger forward a fret and another backward a fret. Experimenting. And do-able on stage.
Every guitarist has to learn the cowboy chords in all the shapes. And the sevenths and major sevenths, and the sus-2’s and sus-4’s. After that, it depends on what genre they are aiming for. As for learning lots of arpeggios?
Only be-boppers do that, and be-bop dominates (non-classical) music teaching, because it has rules. (Of course, classical guitarists learn arpeggios, but that’s because a) Bach, and b) treating a sequence of notes across the strings as an arpeggio - and therefore a “chord shape” - is a way of learning the piece.)