For some problems it is useful to know only with a view to choice or avoidance, eg whether pleasure is to be chosen or not, while some it is useful to know merely with a view to knowledge, eg whether the universe is eternal or not; others, again, are not useful in themselves for either of these purposes, but yet help us in regard to some such problems; for there are many things which we do not wish to know in themselves, but for the sake of other things, in order that through them we may come to know something else.