 Like so many issues in natural philosophy, philosophers working in the falsafa tradition took their lead concerning temporal topics from Aristotle. Thus most Arabic-speaking philosophers defined time as the measure of motion with respect to priority and  posteriority.[10]  Although a number of the most discussed issues and problems associated with time concerned the eternity of the world, and so in a sense belonged to metaphysics, there were some pressing questions concerning the nature of time that remained wholly in the domain of natural philosophy. Arguably the most important of these physical question concerned clarifying which motion or motions time measures. Averroes presented the problem at stake nicely in an extended digression his Long Commentary on the Physics (Averroes 1962, 178F-179I).