 This passage illustrates the tenor of the Medieval derivational approach. Aquinas articulates what appear to be principled metaphysical principles concerning the way in which a predicate can be, in his words, ‘taken as being in a subject’. There are two such ways: (1) essentially and absolutely; or (2) essentially and not absolutely but with reference to something else. The latter way corresponds to the category of relatives; the former, to the categories of quality and quantity. Aquinas then divides the former way of being in a subject in terms of form and matter. He claims, strikingly, that the category of quality flows from form and that the category of quantity flows from matter.