Primary Melody (PM)
Primary melodies (PM) are the most important lines in a musical texture. In homophonic textures, there is usually only one primary melody (a), but in polyphonic textures, where the lines are of equal importance, there may be several primary melodies (b).
Although the primary melody frequently occurs as the highest part in a composition, it can reside in other positions.
Secondary Melody (SM)
Other melodic lines that are not equal in significance to the primary melody are called secondary melodies (SM).