In a clearly major tonal context, borrowing from a parallel mode does not alter the fact that the progression is still clearly major tonal.
1. Borrowing a ivm from the parallel minor/aeolian does not cause the progression to cease to be major tonal.
2. Borrowing a bVI from the parallel minor/aeolian does not cause the progression to cease to be major tonal.
3. Borrowing a bVII from the parallel mixolydian does not cause the progression to cease to be major tonal.
So, I see no reason that borrowing a chord from the parallel lydian would necessarily cause a progression to cease being major tonal either.
Borrowing is just putting your tippy toe into the water, it's not diving in head first and getting soaked to the bone.
scales, modes & chords:
the primordial building blocks of music
w/ Schell Barkley
~ the meaning of life is to create ~
Let me explain a little more theoretically what is meant by the term "altered subdominant", but I'll first bring up another issue I have with the "II7 is borrowed from Lydian" theory.
The first premise in the "II7 is borrowed from Lydian" theory is: since II7 does not contain the 4th note of the scale, it is not subdominant or dominant. However, this does not agree with what I'm calling the older Berklee tonal theory. In the tonal theory, chord sounds are characterised as follows:
Tonic: stable, no scale degree 4, scale degree 3 most important, representative chords include Imaj7, IIIm7, and VIm7.
Subdominant: less stable, scale degrees 4 and 6, 6 most important, representative chords include IIm7 and IVmaj7.
Dominant: least stable, scale degrees 4 and 7, representative chord V7.
Subdominant minor: modal interchange chords borrowed from parallel natural minor, scale degrees 4 and b6, b6 most important, representative chords include IIm7b5, IVm7, and other chords we have posted about previously.
Now let's look at II7. It contains the most important subdominant scale degree 6. It is built on the same tonal supertonic root as IIm7. The chromatic alteration is to scale degree 4. So it functions like a subdominant IIm7 but is brighter sounding. It's like altering the 5 of a V7 chord to increase the tension to resolve to I. Altering the b3 of the IIm7 to a 3 to produce a II7 changes the chord color but not the functionality.
As I mentioned before, I often find II7 very effective later in a tune where subdominant expectations have been established. This touches on a lot of what Michaelsorg posted and I agree with fully. Many times you see II7 in an larger section where the overall subdominant functionality is pre-dominant. But within that higher pre-dominant functionality there is inner plagal functionality of II7 to I. Or you hear II7 hanging with its subdominant buddies IV or IVm earlier in a tune. Sometimes it just subdominantly cadences to I all by itself. As we see in many Beatles examples, the effect is often like opening the curtains to let a little sunshine into the subdominant room ("Here Comes The Sun").
This for me completely explains the "why" for II7's common tonal resolutions. No modal theory needed.
Here's a tune of mine that uses II7 exactly in a connection that you had mentioned: with iv min. The feeling again is uprooted - in this case, the feeling of being born in the wrong era (no doubt shared by many jazz musicians!) But being able to enjoy this feeling is what makes it possible to be an artist!
I start with some lyrics:
Grab your | coat and get your | hat, leave your | worry on the | door - step |
I have a nice melody in C major:
E D | C D E G | E, E Eb | D C A F | E D |
Now I need some chords. C is the logical first chord. I want to musically imply that we are going to leave the worrisome place we are starting from. So after we tonically grab our coat and hat for two measures, let's leave and head over to the subdominant area in measure three:
| C6 | C6 | Fmaj7 |
Good start, the IV chord in measure three provides the right feel, but the two measures worth of C chord seems too long. But I still want a tonic feel. The E melody note starting measure two is the highest note in the melody and the tonic defining note, so something special here would be nice.
I first try the tonic substitute chords in measure two. Relative minor Am7 provides downward minor effect, not what I'm looking for. Tonic sub IIIm7 moves upward, but still is too minor sounding.
Since I want to move to IV in measure three, how about C7 as V7/IV in measure two? That's better but still too similar to C. Let me try some voice leading using C augmented. That leads nicely to F but still is not exactly what I'm looking for.
How about the special function II7? That often resolves to IV. But that is not the effect I'm looking for either, maybe because the E has taken on a 9th sound. I really want to focus on that E note.
Then I remember - any diatonic chord can be chromatically altered to produce a brighter effect. We return to the IIIm7 tonic sub and chromatically alter it to produce an E7. Perfect!
Usually an E7 in the key of C would be expected to function as a secondary dominant and resolve to Am7, and if it goes somewhere else you would say it is a deceptive resolution. But if it moved to Am7 that would give me yet another measure of a tonic chord, and I want the third measure to be a subdominant area. So in this case, the E7 functions simply as a tonic color chord. Might this have been the teacher's reasoning?
Of course we get the extra benefit of the chromatically altered G# now leading us to the most important subdominant scale degree 6 (A), giving us an extra lift into the F chord. The newer Berklee harmony class classifies III7 and VII7 as Auxiliary Dominants, meaning a dominant seventh chord that has strong upward chromatic resolution. Root motion is up a half step as well as most other harmonic movement.
Coming back to II7.
"Sgt. Pepper´s Lonely Hearts Club Band" from the Beatles even starts on II7 in a bluesy context.
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