Peter Auriol was one of the most influential authors of the generation after Scotus. He developed an anti-realist ontology (he denied the extra-mental existence of common natures and consequently the necessity of a principle of individuation) and a new epistemology. In his view, the mental world is somehow richer than the extra-mental one, since our mind can abstract general notions (such as humanitas) that are not matched by general objects in reality. The article is aimed to show how, according to (...) Auriol, the individual things existing outside are the grounds on which all our notions (even the general and abstract ones) are based. Accordingly, the first section analyzes the internal composition of the individual things: material suppositum and singular form, which are interrelated as potency and act. The second section deals with Auriol’s theory of knowledge. In particular, it focuses on the relation between our notions, both concrete and abstract, and the metaphysical parts of extra-mental individuals. The general, abstract notions originate from the formal parts (the singular substantial form) of extra-mental individuals, while the concrete notions from the whole individuals. (shrink)