Plagal cadence: IV to I, also known as the "Amen Cadence" because of its frequent setting to the text "Amen" in hymns. However, William Caplin disputes the existence of plagal cadences: "An examination of such a cadence rarely exists...In as much as the progression IV-I cannot confirm a tonality (it lacks any leading tone resolution), it cannot articulate formal closure. Rather, this progression is normally part of a tonic prolongation serving a variety of formal functions - not, however a cadential one. Most examples of plagal cadences given in textbooks actually represent a postcadential codetta function: that is, the IV-I progression follows an authentic cadence but does not itself create genuine cadential closure."A few days ago I slapped together a big "favorites" playlist for Winamp, and have been listening through it to see what I should delete or add. Just heard "Diggy Diggy Lo" by Doug Kershaw. The song ends, and suddenly there's this weird unresolved sub-dominant (IV) chord tacked on at the end, which made me do a mental WTF?
I remembered the IV-I cadence was called the plagal cadence, not from college, because I don't think I ever heard the term there, but from much earlier when I was learning music theory at a summer church music camp.
I'm almost certain I've never seen a real plagal cadence used in any hymn, and I'm pretty sure it's frowned upon in classical music theory. I've only seen it used in a tacked-on "amen" at the end of a hymn, and which no gospel singing group or congregation that I've been part of has ever actually sung--it's just ignored. Classical theory--which is also used for traditional hymn composition--insists upon a closing "authentic" or "perfect" cadence, V to I (dominant to tonic).
So what's this all about? Nothing really. Except I'm going to have to figure out some way to work that phrase "postcadential codetta function" into a conversation sometime.