In the harmonization of a given melody the student is confronted by a new difficulty. Not only must he see that the harmonies are properly connected, but he must find the chords which shall best answer the demands and purpose of the melody. We cannot see from the melody itself what are the chords appropriate to it; for every tone of the melody may belong to several different chords, not all of which would answer the appropriate harmonic purpose. The mere fact that one of the notes of a melody fits into a certain chord, does not justify our application of that chord. Further, we must see that the chord demanded by the melody, be such that it can be legitimately connected with its neighbors; that the voice-leading be good; and finally, that at certain points of the melody there shall occur special harmonic formulas, such as Cadences.
In almost all forms of popular music (and most forms of so-called classical music) the basic composition is a combination of melody and harmony. The underlying chord progression propels the composition forward and, in many cases, guides the movement of the melody.
In fact, most melodies are composed of notes that exist in the underlying chords. If you examine a melody, you’ll find that its main notes—what are called the structural tones—are often one of the three notes in the chord’s basic triad. (Or, in some instances, an extended note from a seventh, ninth, or eleventh chord.). The relationship between melody and chords works the other way, too. You can, with a little practice, use the notes of a melody to construct the accompanying chord progression.
Deriving Chords from Structural Tones
Probably the easiest way to fit new chords to a melody is to deconstruct the melody into its most important notes—its structural tones. A typical melody will have no more than one or two structural tones per measure. (The other notes are connecting or embellishing notes.) The chord you apply to a structural tone should include the structural tone as one of the three notes of the basic triad.
Now comes the work of fitting chords to these structural tones. We could apply one of three chords that include the structural tone in the triad. As we continue on in this fashion, we can come up with any number of interesting chord progressions. Once you’ve assigned the chords to the structural tones, return the melody to its expanded state. Note that when using the structural tone method, there is no right or wrong way to decide which chords to apply.
Other Tips for Harmonizing a Melody
- There are other points you need to consider when fitting chords to a melody
- Try some common chord changes first. You’d be surprised how many melodies fit with the I-IV-V progression.
- Generally, the slower the tempo, the more frequent the chord changes. (So if you have a long whole note, or a note held over several measures, expect to find several different chords played behind that single note.)
- Work backward from the end of a melodic phrase, remembering that most major-key melodies end on the I chord. You then can figure out the cadence leading to the I, and have half the melody arranged fairly quickly.
- Chord changes generally fit within the measure structure, which means you’re likely to see new chords introduced on either the first or third beat of a measure.
Writing a Melody to a Chord Progression
You don’t have to start with a melody; you can base your tune on a specific chord progression and compose a melody that best fits the chords. Theory tips:
- Stay within the notes of the chords—at least for the main notes in the melody.
- Try to find a logical line between the main notes in different measures.
- Use notes that emphasize the quality of the underlying chords.
- Once you pick your main tones, fill in the gaps with passing tones.
- Come up with an interesting rhythmic motif, and repeat that rhythm throughout the melody.