APPENDIX A: VOICE LEADING OVERVIEW
Chromaticism - Background
16th century polyphony is essentially a modal system. Chromatic alternation of notes was only carried out according to certain rules referred to as musica ficta. This was done mostly to enhance the cadences. In the following example, we can see in a) how the seventh degree of the scale was raised a semitone at the cadence. This creates a leading note that is a semitone below the final. This example is in the Dorian mode. Note that the preceding C in the Bass was not altered. Only at the cadence was the 7th altered. We should not confuse this with the major/minor key system.
At b) the 7th of the scale is not altered because in the Phrygian cadence the bass descends a semitone and so the top line must ascend by a tone to maintain a consonance between the melody and bass. This cadence only occurs in the Phrygian mode and creates a characteristically different sounding cadence. (Note: in later tonal music, this is used as a kind of imperfect cadence where the bass descends a semitone to the dominant in the minor key.) At b) we can see a different type of chromatic alteration: the third degree of the final chord is made major by the chromatic alteration of the note G. This could be carried out in any of the minor modes: Dorian, Phrygian and Aeolian, where the third was present. This is sometimes referred to as the Tierce de Picardie and remained in practice well into the baroque era.
A further kind of musica ficta involved flattening the B or E of the scale, as this was sometimes necessary in order to avoid the interval of an augmented 4th or to form an auxiliary note of a semitone movement.
Originally, none of these chromatic alterations were notated in the score. It was left to the performer to know when to add them. In later transcriptions, the editor usually notated them fully or showed them as optional sharps or flats.
Once the major/minor tonal system had become established, more flexibility was possible in the use of chromatic notes. All of the voice leading patterns discussed in the previous topics were now possible with chromatic variations. And these in turn resulted in new chromatic chords and new chromatic voice leading patterns. These are summarised in the following sections.