Thanks man, I appreciate it.It's sad to see TC go this way but I suppose it's past it's shelf life.
So was I even partially correct with my speculation?
I think you were entirely correct to say that the song changes key. 12 bars of music is more than enough to constitute a musical statement in a key and then it is followed by a change of keys, especially to a near neighbor key (in the circle of fifths sense)), C or Am <->G or Em or C or Am <->F or Dm. They share all but one tone in common.
Although it is useful to look at the chord tones in a chord progression for a clue as to the possible underlying scale (as you have done), I don't believe that it bears fruit in this example. For not all chords are "equal" in weight in a given progression, especially in blues and jazz. One must consider the "role" of the chord within the progression. There are well used patterns in music where these non diatonic "foreign" chords show up in what are otherwise straight up major or minor chord progressions.
Point 1: Used as half step tension creators and releasersFor example if we look at that bar with the Eb7, we notice that all that chord is doing is creating some tension by leaving a few bars of D7 by walking to Eb7 for a bar, and then returning to more D7, so it created some tension in that section of endless D7 by walking up a half step before being released with a return to D7. This isn't something I would place a lot of weight on as far as helping us understand the key. This is best understood by playing it, and getting a feel for the common ways that blues and jazz players move in half steps to and from important chords like the tonic (I), sub-dominant (IV), and dominant (V).
The type of analysis you were performing sometimes doesn't bear fruit when we listen with our ears or see this common "half step up" or "half step down" kind of movement.
This is especially true and dramtically illustrated in Blues Turnarounds, where before returning to the I chord in bar 1, a turnaround is employed.
Example: in common 12 bar blues in G major, we commonly see something like
Bar 11: G G7 Gdim7 Gbdim7
then in
Bar 12: G D7
then its back to the I chord (G) for bar I to begin again.
And none of those chords give us a clue concerning the key, its just bluesy stuff in a classic turn-around (a la Robert Johnson, and all the great old blues players).
Notice the Gbdim7 is a perfect chord for moving to G. This type of chord can also commonly be used as a passing chord when moving in whole steps such as from A to G, as in A to Gbdim7 to G. Again, giving us no insight into the key of a piece of music.
So, we have to be careful not to draw too many conclusions from the chords that are listed and ask ourselves what is its role in the progression, sometimes they are obvious half step movements into and out of the I, IV, or V chord.
Another example: This is common too for V chords in 12 bar blues. For example, in the key of G major: the bars with V chords sound something like this:
such as the 9th or 12th bar: D5 Db6 D7 Db6
Simply walking around before returning to the I chord or possibly the IV chord
Another example: the bII chord is used in jazz a lot to simply create a way to step into the I chord.
Point 2: Watch for bIII and bVII chords in Jazz, Blues, and RockWe are sometimes wondering what is going on when we encounter these chords in a progression that otherwise looks like C major all the way.
We know for example that the key is C major, yet there are Bb7 and Eb7 chords all over the place. Huh? is the key moving counter clockwise around the circle of fifths to F or Bb from C major? probably not.
+something to ignore+ Is the music simply modal (music which is centered around a modal formula) and not tonal (music with a definite key). Well, it could be in jazz for sure, especially a la Miles Davis, but again probably not. (I shouldn't even bring this up in a discussion of keys in jazz, but I couldn't resist). +/something to ignore+
Yet the piece of music in C major sure sounds ambiguous, possibly bluesy (because the pentantonic or some blues scale is at work also) yet we are hearing a lot of b7 tones (Bb) and b3 tones (Eb), which might cause our ears to be pulled toward the key of Eb Major/C minor, and thus ambiguous. Well, that's just cool chord progressions in C major for you. Tonal music. C major. Yet, not so diatonic.
These 2 chords (bIII and bVII) are some of my favorites to throw into a major chord progression that is otherwise filled with diatonic chords. Try it. You'll like it.
Especially, if you can exploit their tones in your melodies. Ahh...a couple more tones with some good chords to work with and yet the ear still retains the key and so it doesn't sound modal, atonal, or chromatic at all, and yet my chords aren't endless I IV V or diatonic forms either.
hmm....!?!?!
