Chromatic progressions are modifications of diatonic progressions and involve notes that are not part of the scale upon which the passage in question is based. Generally speaking, they have two functions:
intensified closure - the sense of closure or resolution is heightened by the chromatic notes, the effect is like stretching a rubber band a little bit more before releasing it
modulation - the chromatic note or notes results in the passage moving from one key to another
This section concentrates on the first of these in which the music does not modulate as a result of the chromaticism. Modulation using such chords as diminished sevenths is discussed in the section on key and modulation.
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