blastingas10

Yes that does make sense.

So if my progression is C, F, Am, G, I could insert the D before the G because the D is the dominant of the G (and the G is the dominant of C).

But let's say I went C, F, Am, D and went back to the tonic of C, that would make a key modulation?

Or instead of going back to the C, I could modulate into the key of D and play D, G, B, A (I, iv, vi, v). That's probably not right but the idea of modulation into a different key and playing the same I,IV,VI,V makes sense.