I don understand this dorian sixth that was used in Autumn Comes. Where does it come from?
At the end of a song, the melody is usually brought to the Tonic. In a major key, adding a major 7 to the final chord results in a clash with this melody. Therefore it is often left out, or replaced by the colorful (diatonic) major 6. In a minor key, the major 7 is inappropriate for the same reason (the clash with the melody), the minor 7 evokes an unwanted longing for the IVth scale degree, and the diatonic minor 6 is unstable with a minor triad of the Ist scale degree. The major 6, however, is available to color the final chord. One could say that it comes from the tone supply provided by melodic minor. In that respect it is perhaps a bit confusing to call it ‘the dorian sixth’.
