What do you call the melodic pattern with 3 notes?

Question

I've noticed that in most, nearly all, popular music, the part that the singer sings usually follows the same pattern. Each bar has an emphasized note, and the same three notes are repeated in a specific pattern over and over.

Middle, High, Middle, Low, Middle, High, Middle, Low...

For example, Amazing Grace, C is the middle note, E above that is the high note, and G below the C is the low note. The whole melody is mostly C E C G C E C G C etc etc.

Is there a name for this pattern?

Also, is it always I III I V I III I V I III?

Answer 1

One way to label this is a melody that arpeggiates the tonic chord. To clarify what that means, the melody is only using the notes of the C chord, which is the tonic chord of that key (the chord that has the name of the key, also which has its root on the first note of that key). And it arpeggiates that chord, meaning it goes up and down the notes of that chord, just like your pattern.

Caleb made a good point that plain Arabic numerals, with the "^" above them, specify note names, while Roman numerals specify the chords of a key.

Answer 2

Schenkerian Analysis is a fairly advanced technique if you're just learning about music theory, and it was designed primarily for classical music, but one of its key concepts is prolongation -- the idea that some notes in a melody are more important (more functional, if you will) and can be, in some abstract sense, extended throughout an entire passage of a piece by using various techniques involving other decorating notes.

Prolongation is a very general concept, and there's no requirements for which scale degrees are prolonged, or are used in a prolongation, although the choice will determine the name of the type of prolongation you are using. A few examples of techniques used in prolongation include passing tones, neighbor notes, and arpeggiation. In this particular case, you seem to have a form of arpeggiation being used to elaborate the tonic, C (as Mark points out).