Is the ii V I scale based on the upcoming I scale ? Wouldn't that cause key change?

Question

The key is in E Major.

The chord progression goes like E - C#m - B/F#,F# - B

I thought the chord progressions were I - Vi - V/V - I

But if you see the first bar at the picture, there is A# in the C#m chord.

This got me thinking this is a ii-V-I progression.

But then another question occurred.

Are ii V I chord progression's scale based on the upcoming I ? in this case the B chord.

If it is, doesn't this automatically cause key change ? Because by doing this, your appointing the I to be the tonic.

I never knew deep about the ii V I chord progression, but I thought I could just use it to any chords on the key to just pass by and add more harmonic flavor, but if this is the case, every time I use it to any chord that is not the tonic of the current key, it will cause key change...

Am I getting something wrong here ?

Answer 1

We really need to stop considering 'a key' as purely diatonic notes and chords. Straying into harmonies that are on each side of the 'keys'' place on the circle of 4/5s is so commonplace it doesn't raise much of an eyebrow. As in 'key E', there will be places where F♯ harmony or D harmony crops up in many pieces. When they do, it's often in an ephemeral way - just a fleeting visit to somewhere interesting, then back to basics - known generally as a modulation.

Answer 2

I think you want to look at more than chord names like E, C#m and label your Roman numerals with keys as well as pay attention to phrase endings.

It's important that the section you posted has a second ending volta. It looks like you are at the end of a musical period (two-part phrase group) that modulated to the dominant, and after the double bar the B chord becomes a dominant seventh using an A natural rather that the A# of the previous bar, and moves to an E chord. All of that looks like a very conventional handling of the dominant where the music modulated to the dominant and then modulates back to B being the dominant of E.

Analysis would be like this: |B: ii6/5 I6/4 V7 I ||: E: V7 | I | ...where B: and E: are indicating the keys.

So, when you suggest I - Vi - V/V - I could be re-interpreted as ii V I you are really identifying the modulation. I think your description of the harmony is right on track. You are recognizing a shift in tonic, a modulation. Just add the key labels to make it clear.

When you see a pattern that fits ii V I into a key, it often makes sense to label it as a modulation. Of course you need to look at the phrase context to know if it makes sense as a modulation. If it coincides with a phrase ending, a modulation analysis makes sense.

Answer 3

There is no need of key change here. This is a half cadence. You’ll find this quite often in the first ending of a repeated phrase. The progression I vi V/V can also be analyzed as I (ii V)/ V and we speak of an extension to to the dominant. The 1st bar after the double barline is still in the dominant and the piece continues in E major.

Answer 4

That "A# in a C#m chord" would perhaps be better considered an inverted viidim7/V. Then when the A# appears again, it is in a V/V. Both of these uses of secondary dominance in the 2nd ending make for a very dramatic half-cadence in the music. It may even trick the listener into thinking the key has changed. However, going on into the next measure, we are back at a B-dominant 7, no A#, followed by an E major chord, telling us that the B major chord of the 2nd ending was just a half cadence after all.