The Aeolian mode (or Natural minor scale) and the Dorian mode are two minor scales, that difference for just one note: a minor 6th on the Aeolian, a major 6th on the Dorian. They’re both related to a minor root chord built on different degrees of the Major scale: on the 2nd degree for the Dorian mode, on the 6th for the Aeolian.
In the first part of this video, Am is the root chord built on the 2nd degree of the G Major scale, where D7 is the chord built on the 5th degree. In the bridge section, Fmaj7 and Dm7 are chords within the C Major scale harmonization. That’s why I switch to A Aeolian.
