 Kilwardby’s criterion for classification is the object of the sciences (Alessio 2001, 108–9): “science must be divided according to the division of things about which it is” (DOS 5). “The diversity of sciences”, he says, “results from the diversity of their subject matters” (DOS 108). Sciences are organized, as in the Boethian scheme, according to the level of abstraction of their objects of study from matter. Speculative sciences rank highest (DOS 203) and among them metaphysics. Metaphysics deals with being without qualification (simpliciter), whereas mathematics and physics deal with particular kinds of being (DOS 323; NLP II.11, 417). Metaphysics considers substance and its principles – matter and form – per se, that is, apart from change and privation, whereas physics (natural philosophy) considers substance as mutable and therefore matter and form (and privation) as principles of change (DOS 232); mathematics deals with changeable material things but not insofar as they are material, rather, insofar as they are abstracted from motion (within the sciences of the quadrivium, where the order is astronomy, geometry, harmony, and arithmetic).