My son Miles recently mentioned to me that I have a song lyric to quote for just about every occasion. We spent several days in the Black Forest together, and apparently, I would quote lines whenever I heard a phrase that reminded me of a line. For example, "take it easy" leads me to quote The Eagles. If I hear the phrase "the last day," I'll quote Al Stewart's "The Last Day of June 1934."
Once he pointed it out to me, I began to notice just how often I think of phrases from songs. And I began to wonder whether I think of phrases from poems very often. I certainly quote Eliot's "Let us go then, you and I" all the time—in fact, it crosses my mind whenever someone says "Let's go!" And there are other poems that have tag lines in them that bring them to mind when I hear echoes of those lines.
But mostly it's songs that I quote in such contexts, not poems. For years now, I have argued that poetry and song lyrics should be treated as members of a larger category that I call "verse"; attempts to strictly distinguish poems and lyrics have never been convincing to me. Verse that is not written to be sung tends to have more enjambment than verse that is written to be sung—a side effect of the effect of melody on lineation. But that doesn't seem to me to be enough to say that poetry and lyrics are different in essence.
Miles's observation about my quotation habit suggests a way to articulate another difference between poems and songs. The phrases that lead me to quote songs tend to be unremarkable, even cliched: "take it easy" is an empty little formula, not exceptional at all. There are many more such phrases in lyrics than in poems; in contemporary poetry, formulas and cliches tend to be avoided, while songs are extremely forgiving when it comes to the use of such well-worn language. It's fun to hear a catch phrase and sing along with the singer; it's boring to read a catch phrase in a poem (unless the poem brings it back to life in some way).
That still doesn't seem to me to be enough to strictly distinguish the two kinds of verse from each other. But it helps me understand my quotation habits.
For a discussion of my understanding of "verse," see the fourth paragraph of this post.