Topoi in Avicenna's Logic; From Strategies of Debate to Fallacies of Definition

Aristotle and Peripatetics used topoi as the strategies of debate، but Avicenna changed their function to the fallacies of definition. This is one of his outstanding innovations to which the modern scholars didn’t pay attention. This innovation، on one hand، is related to Avicenna’s logical purposivism; and، on the other، to his bipartite logic. By the former، I mean his belief that the main purposes of logic are: 1. thinking validly and، 2. avoiding thinking invalidly، and any part of Aristotelian logic، not efficient for either of these، either should be eliminated (such as Rhetoric and Poetics) or its function should be changed (such as Dialectics). By the latter، I mean a new logical order by which Avicenna divided Aristotelian logic into two parts: (i) theory of definition and (ii) theory of inference. Now، if we put the mentioned innovation along with the Aristotelian thesis that ‘all sophistic refutations are syllogistic fallacies’، we obtain، in parallel with bipartite logical theory، a bipartite logical pathology، i. e. fallacies of definition and fallacies of inference.