It seems to me that a lot of beginning learners have trouble understanding when to use the cases, regardless of the book they are using. They often mention that the book does not give "the rules" or does not explain it well enough. If anyone would take the time to do so, could you tell me what exactly it is about cases that is hard to learn - but not only that, why is it that your text does not explain it adequately? It would be interesting to see how your text goes about doing it. If you were presented with a series of examples where it was used, would that be enough for you, or would you still prefer a hard and fast rule?