Chord sequence
Em7 A7
In every key
Four-note rootless voicings in their two forms, with the 3rd or the 7th on the bottom, played over the root.
Heard in D major
All the chords
The building block of jazz harmony: a minor 7th chord on the 2nd degree moving up a fourth to the dominant 7th on the 5th.
A two-chord vamp of a minor 7th on i and a dominant 7th on IV, both from one Dorian scale.
Over Em7 · ii7
Mode 2 of Major
Over A7 · V7
Mode 5 of Major