You would never hear any song played twice in the same way. The words were retained, but within a certain frame there was great latitude, and the musician could improvise to his heart's content; and the more the variations and combinations, the greater the musician.
The technical history of modern harmony is a history of growth of toleration by the human ear of chords that at first sounded discordant and senseless to the main body of contemporary professional musicians.
PRESIDE, v. To guide the action of a deliberative body to a desirable result. In Journalese, to perform upon a musical instrument; as, "He presided at the piccolo."