The present essay is the first part of an analysis regarding aspects of Aristotle’s ontology. Aristotle’s ontology is, in my opinion, a formal ontology that examines the fundamental structures of reality and that investigates the features belonging to entities such as substance, quantity, quality, universals. Aristotle’s ontology investigates, moreover, the reciprocal relations existing between these entities. Aristotle’s interpretation of universals is not, in my opinion, a nominalist interpretation of universals: I do not think Aristotle regards universals as being only mental (...) entities. Aristotle, rather, aims at the differentiation between the realms of reality to which individuals and universals belong. In this part of my investigation, I first expose my interpretation of the fundaments of Aristotle’s ontology. Thereafter, I concentrate my attention on chapter Metaphysics Zeta 13: I comment on Aristotle’s investigation regarding the ontological features belonging to the universal qua universal and to the substance qua substance. I analyse the ontological laws that Aristotle finds about universal and substance: substance and universals are considered by Aristotle as mutually incompatible entities. The analysis shows that a false interpretation of the features of the universals endangers the whole ontology. Moreover, the Third-Man-Regress, which is one of the consequences of the misunderstanding of the position of universals in the reality, is regarded as the key to the interpretation of one of Aristotle’s aims: Aristotle aims at the foundation of a typological ontology putting individual entities and universal entities on different levels of reality. The danger of the Third-Man-Regress is avoided through the introduction of a new ontology, that is, through the introduction of the typological ontology of the entities. (shrink)