Materia e individualizzazione della forma nella 'Metafisica' di Aristotele: la posizione del problema in Z 7-9

This article is the shortened version of a paper delivered at the International Conference on 'Existence and Identity' held at the Catholic University of the Sacred Heart in Milan, May 5-9 2014. These two main topics in contemporary ontology, prove to be central in Aristotle's Metaphysics as well. I seek here to pinpoint very synthetically, how complex the Aristotelian conception of identity is, and how deeply connected with that of ousia-existence. If applied to sensible substances, identity has to justify at the same time difference (in regard to others) and sameness (in regard to itself). This requires to overcome both the physicist and the Platonic simple conception of matter as underlying principle of changes. In the most disputed chapters Z 7-8 Aristotle thickens his understanding of hyle as material cause of a singular substance, that is as potentiality of a specific form.