 One such supplement involves Spinoza's attempt to extend the range of application of Descartes' collision rules. Descartes' collision rules are limited in scope to the special case of bodies moving along a single line. In a scholium following a corollary Spinoza adds to Descartes' third rule, Spinoza explains that the vexed Cartesian term “determinatio” (determination) signifies not just the direction of a motion, but also a force of motion along that direction (PCP IIp27s). He then attempts to demonstrate how the Cartesian collision laws can be extended to oblique collisions, by showing how this force can be resolved into components by the rule of parallelograms. Spinoza's confused attempt fails, but this failure is not of much interest on its own. Given that the oblique case is surely more ordinary than the collinear case, and given that generality of application is something one would surely want in collision laws, what is interesting is why Descartes did not himself attempt to provide rules of more general coverage, and why Spinoza felt that he had to do so.