Watch the Dorian Defined online guitar lesson by Brad Carlton from Chord Studies: Double-Stops Vol. 1
As I mentioned at the end of the last example, Examples 11 and 12 could apply to both A Dorian and A Aeolian because we didn't encounter F or F♯. This example clearly defines the Dorian mode. Our last chord D/A has an F♯ which indicates that we are in the key of A Dorian. The notes of the A Dorian mode are identical to the notes of a G major scale. The only difference is where our tonal center or "home" is. Modes are commonly used in music and even an elementary understanding of how they work can go a long way in developing your ear. If you haven't come across modes before try reading up on them.