The sound of sense, then. You get that. It is the abstract vitality of our speech. It is pure sound – pure form. One who concerns himself with it more than the subject is an artist. But remember we are still talking merely of the raw material of poetry. An ear and an appetite for these sounds of sense is the first qualification of a writer, be it of prose or verse. But if one is to be a poet he must learn to get cadences by skillfully breaking the sounds of sense with all their irregularity of accent across the regular beat of the metre. Verse in which there is nothing but the beat of the metre furnished by the accents of the polysyllabic words we call doggerel. Verse is not that. Neither is it the sound of sense alone. It is the resultant from those two. There are only two or three metres that are worth anything. We depend for variety on the infinite play of accents, in the sound of sense.
— Robert Frost, letter to John Bartlett, July 1913