What scale could be used for this progression? Em C D B
 

I'm very fond of playing the following progression: E minor, C, D, B. It has a little bit of a middle Eastern/exotic feel. I'm curious what scale I could use to solo over it? What key is this progression in? And what would be the number system for these chords? I very much appreciate any help, I'm new to music theory.

PS: a good example of this progression is Desert Rose by Sting (in a different key though).

The scale is E minor:

E F# G A B C D E

It's the same as G major--the F is sharped in both cases. Again, the key is E minor or G major (the signature of both look the same). All the key signature really tells you is what scale you're using. You can't play any other scale over this or will be out of tune. Maybe you meant mode. Which mode you use depends on the effect you want. Try Dorian--that's always a good one:

F# G A B C D E F#

But it's the same thing, you say? It's just starting in a different spot? Aye, that it is. But the relationships between the note positions are different. Notice in the E minor scale listed above (called Ionian mode), for example, that the first two positions are E and F# which is a whole step. Now look at 1 and 2 in the Dorian mode: F# and G, which are a half-step apart. Yes, that makes a difference.

Or you can play in Ionian mode and let the bass play in Dorian. We do that in jazz a lot.

Have fun.

Actually, what I just wrote is wrong. You're in Aeolian mode not Ionian if you're playing in E minor. Sorry. So Dorian would actually be A B C D E F# G A. But try em all out and see what you like best. Once again, sorry the lapse. I'm still recovering.

That progression in E minor would be i VI flat-VII V. You get a little bit of chromatic flair from the resolution between the flat-VII and V chords, since flat-VII only works in the Aeolian mode. The V works fine since it's a simple dominant chord. Scale-wise then, you can play comfortably in E natural minor until the B chord, at which point you'll want to raise your D to a D-sharp. And maybe C to C-sharp, but if you like the exotic sound, keeping it at C will give you that.

As others have said, you can do E minor over all of that, then you need to switch over to E harmonic minor on the B chord. You can also do E minor pentatonic for the majority of the progression, too. What instrument do you play? Guitar? (Assuming from your user name.) Try these out:

Hi all, sorry for my late response... Thank you everyone so much for your thoughtful replies!

I've discovered that playing E natural minor then switching to harmonic minor over the B chord is a great solution. However I've also discovered that there is a scale (or mode of a scale) that works wonderfully! It's the Phrygian dominant scale, also known as the Spanish Phrygian scale or gypsy scale. It is the 5th mode of the harmonic minor scale!

Well I've done a bit more reading and I'm a little disappointed that I was wrong. I thought the B Phrygian dominant scale was perfect. It's notes are B C D# E F# D A. Close but no cigar. I just need that darn D# to drop to a D! Are there any scales that contain the notes B C D E F# A?

Please excuse my limited understanding I'm still learning. Thanks again all! Music theory is really exciting!

So I could basically play E natural minor (E F# G A B C D) and switch to E harmonic minor when I hit the B chord to grab that D#, or play E harmonic minor, (E F# G A B C D#) and switch to E natural minor over the D chord to grab the D note.

Is this all correct? Any other tips/ tricks I could do? This is beginning to make sense I think.

Both are technically "right," but sticking mostly with harmonic minor sounds more interesting to my ear. Playing E harmonic minor over a C-chord is trickier than natural minor, but it can be really cool if you know how to use the dissonance between the G and the F-sharp or the E and the D-sharp. Once you get down to this point, the easiest thing to do is just play and let your ear figure out what you personally like.

Allow me to point something out. This is the E harmonic minor scale:

E F# G A B C D#

This is the B phrygian dominant scale:

B C D#E F# G A

Notice anything? They're the same notes. If you play B phrygian dominant, you're essentially playing E harmonic minor. So, the original equation still fits: E natural minor (E F# G A B C D) over the first three chords, then E harmonic minor/B phrygian dominant (E F# G A B C D#) over the last chord. You won't be able to play one single pitch collection over the entire progression. However, depending on what you're doing, you might like the sound of E minor pentatonic (E G A B D) over the whole thing. It's an E natural minor scale minus the 2nd and 6th notes. When you reach the B chord, when you play D, it will sound like a B7(#9) chord (B D# F# A D):

It can be interesting. If you don't like the way that sounds though, you're pretty much going to have to suck it up and switch to E harmonic minor when you get to B.