Scales are frequently featured as what my composition professor liked to call “gestures;” that is, a fast upward scale as a lead-in to a big passage, or a fast downward scale that lands in a loud “boom.” (Go listen to some Phantom of the Opera if you don’t know what I’m talking about.) The idea behind a gesture isn’t the notes themselves but rather the feel of the motion.
When a scale is used as part of a tonal composition, each pitch of the scale has a specific role in defining the key. Those roles are irrelevant when the scale is used merely as a gesture. When you make a melody out of the notes in a scale, though, the success of your melody depends entirely on how you follow or break the rules dictated by the pitches’ functions.
If you’re using the scale a key is based on – you’re not, for whatever reason, using the A major scale in the key of B flat minor, or something like that – then the root of the scale is also the tonic of the key. The Do of the scale is your home pitch. As the home pitch, Do is the single most stable pitch of the scale. Because of the acoustics behind the harmonic scale, the next two most stable pitches are, in order, So and then Mi because of their close acoustical relationships to the tonic. Note that these three pitches, Do, Mi, and So, form the tonic triad of your key. The resonance of these three pitches makes the tonic chord of your key the most stable chord.
The remaining pitches in the scale are Re, Fa, La, and Ti. These four pitches lack stability within the key and tend to resolve to the three stable pitches. The biggest determining factor is distance. Fa is between Mi and So, both of which are stable pitches. But because Fa is only a half step away from Mi, it wants to resolve there instead of pushing through the whole step to So. Ti is a half step away from Do, with the next nearest stable pitch being So a major third away. Without a doubt, Ti will resolve to Do. Similarly, La will resolve to So. The Ti-Do and Fa-Mi resolutions are the two strongest key-defining melodic motions because of the strong half-step pulls.
Now, what about Re? Re can resolve either upward or downward. Do is a more typical resolution because of its extra stability, even though Mi is a perfectly acceptable resolution. I’ll return to Re in a moment because the minor scale raises another question for the astute observer.
The same guidelines apply to the minor scale: Do is the strongest pitch, with So and Me right behind. Fa wants to resolve to Me, La wants to resolve downward to So, and Re can go either way to Do or Me. Te, when used, typically resolves down to La on the way to So.
Remember, the minor scale is a rotation of the pitches in the major scale; it’s a different mode of the major scale. The sequence of intervals between consecutive scale degrees is the same, but you start in a different place. That means you still have two half-steps in the scale, but instead of being between Ti-Do and Mi-Fa, they’ve moved to Re-Me and So-La, respectively. This really doesn’t change anything for the melodic function of La, which still tends to resolve downward to So. The Re-Me relationship in minor, though, are the same pitches as Ti-Do in the relative major key. (That is, B and C are Ti and Do in C major but Re and Me in A minor, for example.) This makes Re’s tendency to resolve one way or the other even more equivocal. Do remains the more stable resolution, but the strong half-step tendency toward Me allows for some very interesting melodies in the minor mode.
As with any rule, there are exceptions. The largest three are the upward resolution of Fa to So, the resolution by skip of So to Do, and the resolution by skip of Ti to So. More exist, but these three are the most prominent. And of course, you can completely disregard these rules when writing melodies. They do come in handy when writing chord progressions, as I’ll explain in the articles on Harmony.
- Fa can resolve upward to So when it serves as a passing note between Mi and So and it’s supported underneath with motion from Do through Re to Mi.
- So can resolve to Do, either upward by a perfect fourth or (more strongly) downward by a perfect fifth, when it’s the bottom note – the bass – of a chord.
- Ti can resolve to So downward by major third when it’s neither the topmost note or the bottommost note of a dominant chord (So-Ti-Re).
