(musth1) Mediant and Leading Tone Harmonies

Quick notes on using the mediant harmony (iii/III) and leading tone harmony (vii° in major and minor).


Our main use of the mediant harmony will be to harmonize descending 1 – 7 – 6 soprano lines, where the LT does not resolve back to tonic. You can use iii/III to harmonize scale degree 7. The mediant harmony usually leads to IV/iv (ascending 2nd) or vi (descending 5th). Keep in mind that in minor, 7 will not be raised if III is used.

Leading Tone

The leading tone triad can be used a dominant substitute, but for now we’ll concentrate on using it as a passing chord in a tonic prolongation capacity.

Since vii° is a diminished triad, we will only use it in first inversion (to deemphasize the dissonant interval of the °5/+4 by putting it in upper voices – not combined with the bass). Since the root and fifth form a dissonant interval that wants to resolve, you do not double either chord tone. Always double the third (bass).

With the bass on the second scale degree, and the tonic prolongation function of the chord, you’ll find the LT triad happening with a 1 – 2 – 3 or 3 – 2 – 1 scale degree progression in the bass. The progression will be I – vii°6 – I6 (i – vii°6 – i6), or the reverse, I6 – vii°6 – I.

There are two ways to handle voice leading out of the LT triad. You can resolve the dissonant interval (°5/+4), or you can move in unequal 4ths/5ths. If you resolve the dissonant interval, the °5 will resolve in to a 3rd. The +4 will resolve out to a 6th. Resolving the °5/+4 will result in a tonic chord with doubled root and doubled third, and a missing fifth. If you move in unequal 4ths/5ths, the resulting triad will be complete. You must always move in contrary motion from the doubled third (scale degree 2) in the LT triad, to scale degrees 1 and 3.


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