The primary aim of this course is an in-depth discussion of the central chapters of Book IV (Book Γ) of Aristotle’s Metaphysics, a key text of ontology, where Aristotle reassesses his former (anti-Platonic) commitment that there is no common genus of being – instead being is homonymously divided into the ten largest classes of categories – and hence there can be no science of beings in so far as they are beings. In this work Aristotle argues that a science of substances can at the same time serve as a general ontology. After the first two chapters Aristotle turns to establish some fundamental thesis this science has to discuss – the principle of non-contradiction and the principle of excluded middle. As these are principles any demonstration will have to use, there can be no demonstration of them. Instead, Aristotle goes on to argue that any science, and body of knowledge will have to observe these most general principles.