How to interpret a switch from Em (Aeolian) to Bm?

Question

I'm self taught, so I know just a few things on scales and modes, some probably wrong.

So the other day I was composing a new song. I believe it starts in E minor, as I was playing over the Chords Em and D

Then, came a part with: C, G, C, G (still matching the Em scale) And it felt nice to me to end it with this progression: C, Bm, A#, A.

After this bridge, it feels like I changed the scale, since I'm now playing over Bm, A and soloing over the Bm (B as root). This sounds right to me, but from a musical theory standpoint, I can't explain this progression.

My questions are:

1. With music theory terms.. what have I done ? did I change the song's Tonality? or Scale? or Mode? Or maybe I wasn't really playing Em in the first place ? Is this normal ? are there any rules on how you can do such a change?
2. How can I get back to the the Em scale? I want to close the Bm , A part and return to the Em, D but I can't find a way to do this transition. Do I need to make some Chord progression to do this? any hints on that ?

Answer 1

I would analyze it as follows:

    Em D

is indeed E minor. Since you go from D back to Em, it has a "modal" feel - Aeolian or Dorian. In a diatonic E minor scale, I'd expect to see a d# somewhere. (Not saying that you should, it sounds fine)

    C G

Still in e minor. As you repeat it more often, it might start to sound like G major (the relative major of E minor)

    C Bm

Without any information about the rhythm you're playing it can be difficult to draw a conclusion, but to me this sounds you're still in Em; in fact, C can be seen a a substitution chord for Em (third lower) and Bm as a substitution of D (also, a third lower).

(Not sure of it fits your song but if you have a longish pattern repeating Em D, you could occasionally substitute Em with C and D with Bm just for variety. If you don't overdo that, it may start to sound as an "announcement" of the C Bm progression in this bridge)

    A# A

This is where it becomes interesting. The progression of a major chord followed by a major chord a semi-tone below it often sounds as a VI-V progression in a (melodic) minor scale. The scale that would in this case be Dm; For this reason I would probably analyze it as:

    Bb A

Rather than A# A.

Now you proceed with:

    Bm A

Note that this is exactly like Em D, but a fourth lower (fifth higher). Now, I just argued that the Bb A progression suggested Dm. But the A could just as easily progress to D major. And interestingly, Bm is a substitution chord (third lower) of D.

At this point I will argue that the progression from A to Bm is actually an interrupted or deceptive cadence (http://en.wikipedia.org/wiki/Cadence_(music)#Interrupted_.28deceptive.29_cadence). That is, the A raises expectation to go to D major, but instead, it progresses to the relative minor of D major, which is to say Bm.

Going back to Em is simple - Tim already pointed out that you can simply use a B7. Since you're coming from A, and A B7 is in the melodic minor scale of E minor, the move back to E minor will sound very natural, and doesn't need any extra chords or preparation.

That said, you could spice it up a little to again use substitution chords, this time for Bm and A. These would be G and Fm respectively. So you could do

    Bm A | Bm Fm 

And then restate your C G chords that got you there:

    G C  

If you then let the C follow up by a B7, you get a alot of tension that make the return to Em feel inevitable. (This C B is same thing as what I mentioned before about Bb A - the C B will sound as VI V progression, in this case in the scale of Em)

    G C | B7 B7 | Em

Answer 2

Seems like you start in Em, as you said.The A#/Bb before the A is a tritone substitution for E, the dominant that normally leads to A.Sounds good, works well.It's a common change - Bm - E - A, the oft used ii-V-I.

If you feel that A fits better than Am in the first part, you are probably in E Dorian, rather than Emin. I know there isn't an A featured, but just try each to hear the one that would (if used) fit better.

After this, you could be in A or Bm. If we think in terms of A, then a root of B puts it into B Dorian, which is nearly a full minor.

Getting back to Em might entail using a B or B7 bar as this is the dominant of Em. Before the B bar, a diminished or half diminished (m7b5) bar will be useful to lead the way.The B after some Bm will sound rather like a 'tierce de picardie', although it won't be in its usual place at the end of the whole tune. You may, however, feel that you can make the very last chord an Emaj.This sounds effective and final.