 Another distinguishing mark of quantity is its characteristic (proprium). In the Categories (6, 6a26–35), Aristotle identified it through the fact that only quantities are said to be equal or unequal. Burley does not wholly agree with him because quanta per accidens also are said to be equal or unequal, though in a derivative way (EP, ch. de quantitate, fol. 32rb). Thus, Burley turns to two texts from Aristotle’s Metaphysics (books V, ch. 13 and X, ch. 1) for an alternative account of the proprium of quantity as the measure of what is quantified (EP, ch. de quantitate, fol. 28rb). Moreover he employs this property as the common principle from which the seven species of quantity can be derived (EP, ch. de quantitate, fol. 30ra). In this way, he tries to show that the category of quantity, like that of substance, has an ordered internal structure, and he reasserts the reality and real distinction of quantity against authors such as Peter Olivi and Ockham, who had attempted to reduce quantity to an aspect of material substance. Burley quotes at length from Ockham’s commentary on the Categories (ch. 10, § 4), where the Franciscan master tries to demonstrate that quantity is really nothing distinct from substance and quality. He then proceeds to reject Ockham’s arguments (EP, ch. de quantitate, fol. 30rb–vb).