The Rules of Conduct

In order to distinguish the simplest things from those that are complicated and to set them out in an orderly manner, we should attend to what is most simple. So he specifically picks out astrologers in ignorance of the heavens without having made proper observations of the movements of the heavenly bodies expect to be able to indicate their effects. He's trying to articulate a taxonomy where there are some kind of simple facts that we can undoubtedly conceive of when we have an unclouded and attentive mind.