 Aristotle often made use of indirect arguments from false or impossible positions by adding hypotheses which he himself labeled as impossible. In order to defend Aristotle’s procedure against ancient critics, Alexander of Aphrodisias characterized these hypotheses as impossibilities that were not nonsensical. (For this controversy, see Kukkonen 2002.) Some late ancient authors were interested in impossible hypotheses as tools for conceptual analysis. In the arguments which were called Eudemian procedures something impossible was assumed in order to see what followed. The impossibilities discussed in this way by Philoponus and Boethius show similarities with Porphyry’s characterization of inseparable accidents as something which cannot occur separately but can be separated in thought. These hypotheses were not regarded as formulations of possibilities in the sense of what could be actual; they were counterpossible and not merely counterfactual (Martin 1999).