Yes, Faldage, and I wonder whether this is one rule that is dying out. I'm fascinated with these modals because I do not believe they are taught strictly anymore, at least in US schools. I could be wrong here, and would enjoy reading comments from others who have been taken through instruction on modals in the US schools. Several fine points caught me off guard, and I enjoy learning fine points of grammar, though, you know, I side often with descriptivists.