  The logician treats of categories, which are ways in which concepts are appropriately arranged in the mind. However, because these concepts reflect the ways things are in reality, that is, the natures and essences of things in the world, the logician also deals, albeit only indirectly, with these natures and essences in order to be able to introduce the proper order among them in the mind. The metaphysician, on the other hand, deals directly with the ten supreme genera, not with ways of arranging concepts in the mind, for the purpose of metaphysics is to determine the essences of things.