“Natural Philosophy consists in discovering the frame and operations of Nature, and reducing them, as far as may be, to general Rules or Laws, – establishing these rules by observations and experiments, and thence deducing the causes and effects of things …”. Sir Isaac Newton wrote this in the program he proposed to the Royal Society after he became its president in 1703. It is likely that by “the frame of nature” he and his readers meant its ultimate ingredients, the original components of bodies. One is tempted, however, to take the phrase as referring to the conceptual frame required for the mathematical description and explanation of natural phenomena. Newton himself put forward one such frame in the introductory sections of his masterpiece, the Principia of 1687 (Newton 1726, pp. 1–27). Without it one cannot make sense of the single, simple mathematical law by which he accounts in one breath for heavenly motions and free-fall. Newton's resolve to make explicit the structure underlying his physics sets him apart from the other founding fathers of modern physics; we must go back to Aristotle to find something of comparable breadth and depth. But Newton's conceptual frame, in stark contrast with Aristotle's, involves quantifiable, measurable attributes of things and was designed to fit the needs of mathematics and experiment. It remained the universal frame of physical inquiry until the advent of Einstein's Relativity, and, as we shall see in Chapter Three, it supplied a substantial part of the subject matter of Kant's critique of reason.