So in OP’s example of tracking every song, if I want/need 4’33” in my database of all songs, but I need to keep track of whether cwillu think’s it’s a song for

So in OP’s example of tracking every song, if I want/need 4’33” in my database of all songs, but I need to keep track of whether cwillu think’s it’s a song for some reason (they seem pretty authoritative, better make note of it), I could create a foreign key for that and set it to values like “cwillu said it’s a song”, “cwillu said it’s NOT a song”, and “cwillu has not specified if it’s a song yet”. That’s why natural keys don’t exist.