Take the 2-minute tour ×  In most cases the penultimate note of
the counterpoint will be the leading tone, which must be raised
in minor to establish a sense of tonality. But why is the
leading tone in the Phrygian mode (E-E) the one exception? Even
though it is a minor mode the seventh step of the scale is NEVER
raised. Why?  Transferred from: Few Questions on Counterpoint in
the Tradition of Johan Fux  share|improve this question In the
other minor modes, i.e., Dorian and Aeolian, the leading note
may or may not be raised. This creates a melodic interval with
the supertonic .In Phrygian,raising the leading note gives an
odd sounding interval with the supertonic. I'm only guessing. – 
Tim May 31 '13 at 7:23 @Tim - Again, please refer to my posted
answer. –  jjmusicnotes May 31 '13 at 8:13 @Tim: exactly, an
augmented second (that's from google translate). That is
practically the same as a minor third, and you wouldn't want
thirds in your scale. Especially not in the 15th century. – 
11684 Jun 2 '13 at 14:47 I