 Aristotle discussed various times (e.g., Prior Analytics and Metaphysics) what may happen in reasoning that starts with an impossible hypothesis, and these discussions have to be taken into account as a second aspect in which obligational disputations have roots in Aristotle’s works. When reasoning from an impossible hypothesis one is not to worry about truth but about what follows logically. This is one of the central technical issues in obligational disputations. Discussions concerning an impossible hypothesis have a long history that can be traced all the way from Aristotle to the Latin medieval period in which obligational disputations properly so called were developed. And it can also be pointed out that at the earliest stages of the Latin medieval development of obligational technique, assuming an impossibility (positio impossibilis) was one, or perhaps even the standard kind of obligation to be considered. (See Martin 1993; 1997; 2007; Kukkonen 2002; 2005.)