What makes a pot useful is the hollowness inside that can be filled. What makes a song useful is the emotional response a listener can fill it with. However impressive and well made a vessel or song is, without that hollowness it is not useful.
What is that quality in a song? Evocativeness?
Evocative – tending to bring a memory, mood, or image subtly or indirectly to mind. Yes, that’s it.
I also like redolent – serving to bring to mind. But it also means emitting fragrance, aromatic or, to use a lovely German word, duftend. And that’s misleading, because I am not talking about the emotions of the musician, or even about the piece of music itself, I am talking about the emotions of the listener.
Now, as a musician I have to ask myself which part of my piece of music is useful, or which part can be filled by the listener. In other words, if a musician loses the ability to listen like his audience, he loses the ability to evoke their emotions. At that point one might get so carried away that the pot is closed at the top, with no place to pour anything into…
For me a song (music with lyrics and vocals) isn’t be as receptive a vessel as an instrumental piece can be, since it is already half-filled with emotion/words.
PS: I had this thought last night before falling asleep but since I learned from my grandfather to always keep a notebook in my night table (I have two, actually – one for drawings the other for writing down thoughts) I jotted it down before forgetting.