  Aristotle’s main and most famous discussion of the principle of non-contradiction occurs in Metaphysics IV (Gamma) 3–6, especially 4. There are also snippets of discussion about the principle of non-contradiction early in the corpus, for example in De Interpretatione, and there is the obscure chapter 11 of Posterior Analytics I, but none of these rival Aristotle’s treatment of the principle of non-contradiction in Metaphysics IV. The discussion below mostly concerns the main interpretative and philosophical issues that arise from reading Metaphysics IV 3–6.