 The treatment of fallacies addresses one of the complementary conditions expressed by the definition of logic, which is supposed to deal not only with what is required in order to infer correctly what is unknown from what is known, but also with what is required to avoid error in the case of inferences that appear legitimate without being so. There is a parallel in the case of conception and definition: logic provides rules to identify and construct definitions and at the same time instructions on how to avoid common errors in the process. Avicenna’s analysis of fallacious reasoning attempts to combine (or perhaps force) Aristotle’s treatment from the Sophistical Refutations into a broader scheme driven by more systematic concerns, which even in the extensive treatment of the Cure is rather compact. The analysis of error in defining is usually covered in connection with the Posterior Analytics and the Topics (for instance at Burhān IV, Ğadal, IV, Nağāt 149). I will focus here only on the former.