 Primary substances are the substrate of existence of any other kinds of categorial being, as nothing exists in addition to primary substances but secondary substances and accidents, which both are forms present in individual substances. Like Aristotle (Categories 5, 2b5–6), Alyngton can therefore affirm that primary substances are the necessary condition of existence for any other items of the world: nothing could exist, if primary substances stopped existing (In Cat., cap. de substantia, p. 286). This does not mean, however, that it would be possible to find in the world a primary substance (i) that would not belong to a certain species, and (ii) without any accident inhering in it. It means that, from the point of view of full existence, accidents and secondary substances always presuppose primary substances, as to be a primary substance is to be an autonomous singular existing item (hoc aliquid), whilst (i) to be a secondary substance is to be a quale quid, that is, an inner and essential determination (or form) of a primary substance, and (ii) to be an accident is to be an outer determination or aspect of a primary substance (In Cat., cap. de substantia, fol. 101v).