"I Can't Quit You" was easy - agree. I tend to think the tough ones are generally what we have in front of us so much today. It used to be generally understood that a beat isn't copyrightable. But with "Blurred Lines", that changed. Chord progressions are officially not protected, but with the number of suits that went the plaintiff's way and it was over a common chord progression that everyone has been playing forever, that's now also fair game. Here's one that is worth thinking about: It's about a groove if you really get down to it. Apparently, the plaintiffs really think the groove has been stolen. I personally hear a lot of Marvin Gaye in it. But it's derivative, not a copy. This is the ground we're in today.