The III and VI degrees have weak harmonic functions. However, they are useful for harmonizing.

The VI degree can have both tonic and subdominant functions because it shares two notes with both the tonic and dominant chords. The same is true for the III degree, which shares notes with both the tonic and dominant chords.

The next table summarizes the chord functions discussed:

dominant			VII
	V
					III	weak
tonic	I
					VI
subdominant	IV
			II