Well having read replies and thinking this over, I have changed my mind completely, Lyrics are nothing more than random words thrown together for a rhyme and should never be allowed copyrights!!!. Ha, just joking folks. Yeah, I still think that while yesterday, being used as an example, has it's own flavor, as a tune it would not be copied as is, to make a song, it would never sell, yesterday is too well known, and any song that is so well known would not be something anyone could reproduce exactly in the original tune and sell to the public. So that alone would keep it's autonomy. But, my suggestion still stands.