I've used my sister as foil several times. It's because she's smart and interesting. And when she goes to interpret a story or a song, she wants to know what the author intended it to mean, because that's the right meaning.
I've tried to disabuse her of this notion and convince her that the author is dead and all, not to much avail. My own view is that texts and music and what have you exhibit patterns that you respond to as you try to understand them. You don't need an author's intentions for this to happen, and at any rate those intentions would be just one element in the pattern, not some sort of "right answer."
I remember a high school English class where the beleaguered teacher was trying to demonstrate something about diction. The poem before us used words like "regal" and "royal" and "kingly," and the point was to notice that together they suggested "kingship" as a theme.
"But how do you know?" asked one of the students. A wrestler, thick-necked and -headed, not actually handsome but with the bulk and symmetrical sneer that passed for good looks in the fallen world of high-school aesthetics. He determined that the teacher didn't have, say, a signed affidavit from the author establishing the interpretation she'd suggested, and he sat back, satisfied with himself. Because she didn't really know what the text meant. The author had never told her.
What a fucking tool. Even now I get irritated, and my sister would have been too. I can imagine him now, his features coarsened, his bulk expanded, leading a comfortable, stultifying existence in the small town that it never occurred to him to leave.