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I recently learned that there's a harmonic reason why some scales exist. If you have a minor scale but want to have a dominant V chord, sharpen the 7th degree and as a byproduct you get the harmonic minor scale. If you have a major scale but want to sustain a VII chord, flatten the 7th degree to have a major VII(b) chord; as a byproduct you get the mixolydian mode. Is it useful to think of the lydian mode as a major scale altered in order to have a major II chord in the common II - V - I?

(Regardless of the answer, can someone point me to a tune that uses a II - V - I with a major II chord?)

  • Can someone point me to a tune that uses a II - V - I with a major II chord? - "Waterloo" by Abba. (OK, the V gets extended to V IV V, but that's just a detail). – user19146 Jun 5 '17 at 3:06
  • I learned a lot just from trying to understand this question, thank you! Please figure out how to add graphics so that others may learn as much or more. (Then teach me, heh, I'm still trying to figure out the easiest way to include notation here.) – lauir Jun 5 '17 at 3:09
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Let's think through this in C major:

    G    A    D    G
    E    F    B    E
    C    D    G    C
    I    ii   V    I

These chords are all major with the exception of the D triad, which is minor. But when we make that D triad major, it starts to sound like the dominant of G major (which is also D major). Thus now we're looking at:

    G    A    D    G
    E    F♯   B    E
    C    D    G    C
    I    V/V  V    I

We call that second chord a "secondary dominant" (or "applied dominant") to the G chord, and we read the Roman numeral as a "V of V."

Long story short, this is very common, and is one of the first chromatic progressions students learn in music theory courses. But it's normally just called a secondary dominant; in my opinion, calling a "Lydian II–V–I" runs the risk of someone not recognizing the function of that D chord.

As a really silly example, here is Bobby Darin's "Splish Splash," conveniently in C major. It begins with a C chord, and at "Thinkin' everything was al-" it moves to a V/V, which then resolves to V at "-right," and finally back to I on "Well I stepped."

  • I thought about it a little more and I guess depending on the groove you could also think of it as the II chord is the root, and then you have the common I - IV - VII in mixolydian. – ptn777 Jun 6 '17 at 0:10

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