Harmonization
In music, harmonization is the chordal accompaniment to a line or melody: "Using chords and melodies together, making harmony by stacking scale tones as triads".[2]
A harmonized scale can be created by using each note of a musical scale as a root note for a chord and then by taking other tones within the scale building the rest of a chord.[3]
For example, using an Ionian (major scale)
Reharmonization is the technique of taking an existing melodic line and altering the harmony that accompanies it. Typically, a melody is reharmonized to provide musical interest or variety. Another common use of reharmonization is to introduce a new section in the music, such as a coda or bridge.
A melodic tone can often be harmonized in a variety of different ways. For example, an E might be harmonized with an E major chord (E – G♯ - B). In this case, the melodic tone is acting as the root of the chord. That same E might be harmonized with a C major chord (C – E – G), making it the third of the chord. This concept extends to ninths (E would act as the 9th if harmonized with a Dm7 chord – D – F – A – C – E), ♯fifths (E would act as ♯5 on an A♭ augmented chord – A♭ - C – E), and a wide array of other options.
Typically however, reharmonizations involve not just a single melody note, but a melodic line. As a result, there are often several melodic tones which might occur over a harmony, and all of these must be considered when reharmonizing.
For example, if a melody composed of E♭ - F and G was originally harmonized with E♭maj7, choosing D7 as the reharmonization chord might not be the best choice, since each melodic tone would create semitone or minor 9th dissonance with chord members of the supporting harmony. Experienced arrangers might decide to use these kinds of highly dissonant chords when reharmonizing, however handling this dissonance requires a good ear and a deep understanding of harmony.
