Unless they aren't...which is the problem I'm having with this book. He is seeking an overarching theory, but there are so many subpoints that don't fit, so he creates little categories for them. In the end, we have a list of things the imperative can mean. Is that an overarching theory?!
Don't misunderstand, the book is very helpful and has good stuff. But, how do you decide which category that particular imperative fits? And is that really what we want to do? That's going back to the decoding form of language learning...