  This brings us to the discipline under which categories are studied. Suárez tells us that the division into nine highest genera–he is speaking of accidental genera, although what he says also applies mutatis mutandis to substance–is proposed not only by metaphysicians, but also by logicians in treatises on categories. Consequently, in one way it properly belongs to first philosophy, that is, metaphysics, rather than logic. The reason is that, whereas the metaphysician studies the ten supreme genera in order to explain their natures and essences, the logician does not have this aim in mind. Logic is directed toward the operations of the mind, rather than toward natures and essences, and its purpose is to establish rational ways of thinking. Logic deals with the concepts of the mind insofar as these concepts can be arranged in accordance with certain rules (DM 39, 1; 1861, 25:504b).