Chromaticism refers to the expansion of the diatonic scale through semitonal (halftonal) modification (“colorization”) of its primary degrees.
Alteration, on the other hand, is a specific form of intra-modal chromaticism. It involves a semitonal modification of unstable diatonic degrees (2nd, 4th, 6th, and 7th) within a mode (or key), enhancing their tendency to resolve toward the stable degrees (1st, 3rd, and 5th).
In musical notation, to raise or lower the degrees of the main (diatonic) scale accidentals are used:
Sharp (#): raises by a semitone
Flat (♭): lowers by a semitone
Double sharp (x): raises by a whole tone
Double flat (♭♭): lowers by a whole tone
Natural (♮): cancels any previous accidentals
A semitonal alteration of the unstable diatonic degrees in the natural major scale:
Example 1
A semitonal alteration of the unstable diatonic degrees in the natural minor scale:
Example 2
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