Along the way there's mention of modal mixture and modal mutation; the concept of the plagal cascade (i.e. C-G-D-A-E chord progression that makes up the song); and blues tonality with some comments from Ethan Hein, which, of course, you can get to by way of Ethan Hein's link to Adam Neely's discussion.
Now something that's fun about Neely's presentation is that he points out that plagal cascades are a morphological outworking of the tuning of the guitar. To put that in more colloquial terms, when guitarists let their fingers do the walking they tend to let their fingers be guided by shifts of consecutive fourths that let them use as many open chord root movement shifts as possible. In Baroque keyboard-based music, by contrast, circle of fifth chain progressions were the norm.
Thus "Fly Me to The Moon" and "I Will Survive" use chains of circle progressions (variants of the V-I/V-i/vii-I) in contrast to guitar music that tends to use plagal cascades a la "Hey Joe". Depending on how short the plagal cascade loop is D-A-E could be just short enough to define one of the more prevalent chord loops in rock and blues.
If you use close-chord positions on the guitar you can play E major open on strings 4, 3 and 2; then play A at the usual frets on the same strings; and then play D in first inversion on the same strings. You can cycle back and forth ad infinitum with the E, A, D, A, E progression as a shuffle in this close-chord formulation and just sit on E for as long as you want. A bassist could thump away on a low E while you vamped on some variation of this for a while. What you'd get is a vamp that can, later in a song, turn into a slow D-A-E plagal cascade progression, even if it's just those three chords. If you think of the slow triple meter section of the Rolling Stones' "Midnight Rambler" then you'll hear an example of what I'm referring to. The morphological potential of standard blues shuffle patterns on the fifth, sixth and blue seventh scale degrees has a short plagal cascade sequence that has defined rock and blues in it in embryonic form.
Putting this observation more negatively, if all your theoretical training and music pedagogy is predicated on keyboard instruction you may hear some stupid axioms to the effect that guitarists and rockers and blues musicians "broke all the rules" of classical music. That's a seriously over-sold claim since interval chain progressions like the Romanesca precede the common practice era tonality we may read about in textbooks. "La folia" was around for centuries before it got Baroque era treatments.
But in terms of what's physically easy to play on the guitar given the tuning system nothing feels more rote than an unexamined plagal cascade getting played by some guitarist who understandably loves the effect of the chord progression but can't be bothered to shake things up with some chord substitutions.
Of course ... if you tried playing a plagal cascade a la "Hey Joe" in parallel minor you might get ...
C minor, G minor, D diminished 7, A flat major, E flat major ... you've suddenly modally mutated into something that ... kinda ... sorta ... sounds like a chain of circle of fifths progressions, eh?
That may just be what makes a plagal cascade a plagal cascade. Change the nature of any the chords in the C-G-D-A-E sequence by even one chord factor and you risk mutating it into something like a circle of fifths progression.
Cm, G7, D dim 7, A flat maj 7, E flat maj 7, B flat 7, F minor 7, and C minor 7, for instance, is pretty much not a plagal cascade. The root movements might look the same, there's a sequence of root movements moving along the circle of fifths, but the flavor of the cascade has, it seems, been lost. Or has it? Floating an idea out there.
What seems clear to me, as a guitarist who has also sometimes played keyboard, is that long-term mastery of an instrument eventually means that it's fun to let your fingers do the walking early on but you practice untold hours and think about the craft of music-making so that it's your mind that makes the music with your body, not your body making the music for you because that's what you're used to.
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