ABSTRACT
A common chord modulation turns on a chord diatonic in both keys. The sheer number of common chords available makes modulation to the dominant or relative both effortless and smooth sounding. Lacking the lubrication of a common chord, chromatic modulations often sound more abrupt and perhaps for this reason are less prevalent than common chord modulations. Common chord modulations occur most often between closely related keys—those that differ by no more than one flat or one sharp. Modulations are usually not reflected by a change of key signature unless the new key remains in effect for a protracted length of time. All modulations have what might be called a tonal border. When the music drives across, it enters a new tonality. Sometimes, the tonal border is clear—a single chord that is a signpost announcing the new key. Sometimes, the tonal border is obscured by additional chromatic harmonies that belong to neither tonality.
