From the same above-linked place, English folk music, at least, involves the repetition of a tune - to tell with words or for dance. Traditionally, more-sophisticated polyphony and chords would be found, rather, in church or court - eventually, i.e. Nowadays, of course, many turn up at folk clubs and accompany their songs with chords; I have heard Martin Carthy embellish the tune on his guitar, which sounded good but is probably closer to "art song" (another very old tradition).