These are all good answers. It should also perhaps be pointed out that in practice the difference between laws, principles, theories, and hypotheses are really not so cut-and-dried. It is very much an alive language, rife with contextual connotations, which in some cases allows these terms to be used almost interchangeably. So that's what causes the confusions about them. But when it behooves us to clarify the distinctions, the above answers provide a useful framework for making those distinctions. In some contexts, the distinctions can be quite important, whereas in others, they just don't matter very much. In particular, in actual science research, the distinctions are virtually nonexistent, in education, they are much more important, and in communicating science to the general public, they are paramount for avoiding misunderstanding.