 A second consequence of this approach to the problem of the nature of substance is that, within his system, primary substances alone are substances properly speaking. This conclusion is confirmed by his analysis of the distinctive mark (proprium) of substance: while remaining numerically one and the same, being capable of admitting contrary properties, the modification taking place through a change in the subject itself of the motion at issue. Alyngton appears to think that this description is satisfied only by primary (that is, individual) substances (In Cat., cap. de substantia, fol. 104v). Secondary substances therefore are per se in the category of substance only insofar as they are constitutive parts of primary substances. Thus, secondary substances belong to the category of substance by virtue of the individual substances that instantiate them, since they are not formally substances. In fact, unlike primary substances, secondary substances are forms, and consequently incomplete entities with an imperfect and dependent mode of existence. They require composite substances in order to properly exist. No form as such, not even the substantial ones, is formally a substance, since no form as such has (i) the capacity of underlying potency and act, and (ii) matter and form as its inner constituent. Secondary substances are related to primary substances as formal principles of the latter. It is in this way that humanity and (say) Socrates are linked together. For this reason no secondary substances as such are totally identical with primary substances (In Cat., cap. de substantia, p. 280; see also pp. 281 and 282–283). As a consequence, while ‘man is animal’ (‘homo est animal’) is a sentence to which a formal predication corresponds in the world, a predication by essence matches ‘humanity is animality’ (‘humanitas est animalitas’). Any (individual) man is an animal because of the form of humanity present in him qua its essential constituent, albeit the form of humanity as such is not the principle of animality. Therefore, humanity is not formally animality nor rationality, even though it is animality plus rationality (In Cat., cap. de substantia, pp. 283–284; see also cap. de quantitate, fols. 106v–107r).