 In minor harmony the sixth scale step is usually avoided, and the 13th is not regarded as an available tension.In modal terms, the available scale steps of the mode (or available tensions for the chords) of the diatonic scale steps are those a whole step above the chord tones, and the avoid notes are those that are not.The only exception is the Dorian mode of the second scale degree, where the sixth is avoided although it is a whole step above the fifth; this is because the tritone between this and the third scale step would give an unwanted dominant quality.