The Stoics assign the first rank to substances, and place matter before the other substances. From this it results that the Stoics assign to the same rank their first Principle, and with it the things which are inferior thereto. First, they reduce to a single class both anterior and posterior things, though it be impossible to combine them in this manner. In fact, every time that things differ from each other in that some are anterior, and others posterior, those which are posterior owe their essence to those which are anterior. On the contrary, when things are comprised within one and the same class, all equally owe their essence to this class, since a class is "what is affirmed of kinds of things in regard to essence." The Stoics themselves recognize this by saying that all things derive their essence from matter. Besides, when they count but a single substance, they do not enumerate the beings themselves, but they seek their principles. Now there is a great difference between treating of principles and treating of beings. If the Stoics recognize no essence other than matter, and think that other things are modifications of matter, they are wrong in reducing essence and other things to a common class; they should rather say that essence is being, and that other things are modifications, and then distinguish between these modifications. Further, it is absurd to assert that (among essences), some should be substances, and others should be other things (such as qualities, modes and relations); for the Stoics recognize but a single substance, which does not contain any difference, unless by division as of mass into parts; besides, they should not attribute divisibility to their substance, because they teach that it is continuous. They should therefore say, "substance" (and not "substances"). MATTER CANNOT BE THE PRIMARY PRINCIPLE.