  Notice here the expressed concern with measuring absolute, true, mathematical time, space, and motion, all of which are identified at the beginning of the scholium as quantities. The scholium that follows the eight definitions thus continues their concern with measures that will enable values to be assigned to the quantities in question. Newton expressly acknowledges that these measures are what we would now call theory-mediated and provisional. Measurement is at the very heart of the Principia. It pervades the definitions and scholium on space and time precisely because the primary point of this section is to spell out (in Howard Stein's words) “the empirical content of a set of theoretical notions” [Stein, 1967, 281].