 The difficulty with the reading, aside from the imputation of cowardice to the old soldier, is that it makes nonsense of Descartes’ mechanics, a theory of collisions. For instance, according to his laws of collision if two equal bodies strike each other at equal and opposite velocities then they will bounce off at equal and opposite velocities (Rule I). On the other hand, if the very same bodies approach each other with the very same relative speed, but at different speeds then they will move off together in the direction of the faster one (Rule III). But if the operative meaning of motion in the Rules is the ordinary sense, then these two situations are just the same situation, differing only in the choice of reference frame, and so could not have different outcomes – bouncing apart versus moving off together. It seems inconceivable that Descartes could have been confused in such a trivial  way.[3]