Back in the era when classical music was actually written all composers were schooled in renaissance style counterpoint, that is, the way in which melodies fit together.
Most people's idea of a melody is an elaboration on a progression of harmonic notes, whereas in reality it is the only spontaneous part of a composition. In my view melody is a sequence of notes which manifest something which the artist wishes to express, and this may be disguised by a harmonic progression, meaning that a melody does not have to be a 'tune'. Every great composition has an underlying melodic structure which is its 'soul', sometimes this is immediately evident, such as in Gregorian chant, Indian classical music, or even Mozart, in other works it can be disguised either by polyphony proper, by harmonic notes (romantic music), or through the repetition of small sequences (riffs).
For me, the study of counterpoint has been far more engaging than the study of harmony, because the melodic integrity of the music gives birth to its theory. I recommend Gradus ad Parnassum (the counterpoint textbook used by Bach, Mozart and Beethoven) to anyone interested in learning to compose polyphonic music. This sort of technique could be applied to metal, with some modification. This is more realistic than trying to include classical harmonic principles in metal, where the distortion would get in the way.
Candidate for post the of year. The science of phrase is that of death metal; it's similar to melody, in that each phrase creates a mental image and stringing them together produces a narrative form of music.
