Using the jazz progression (iii7 - vi7 - ii7 - V7 - I7) in C Major, we have (em7 - am7 - dm7 - G7 - CMaj7).
But... I often see this progression wrote or played as: (em7 - A7 - dm7 - G7 - CMaj7)
So, the initial vi (am7) has apparently been changed to (A7)..... aka the minor 7 chord has been replaced with a Dominant 7 chord
I have questions about all of this:
Why is this a common change?
Why... if a Dominant 7 is to be played, am I seeing it wrote down originally as (vi)? If the vi, in this case the chord of am, is never played, why even mention it?
What is the name of this technique in general, so that I can study it further?
In this certain progression, what is so special about changing the (vi) chord & not the others? Why isn't the initial (iii) chord of em changed to E7?