The period at the end of the sixteenth century and the beginning of the seventeenth was one of great importance in the philosophy of the natural world. What had been, up to this point, a single discipline of 'natural philosophy' gradually split into two different endeavours: the philosophy of natural science and the science of physics. Both disciplines share a common subject matter, but they have different purposes and operate in different ways. The philosophy of nature seeks an understanding of the concepts we employ in describing and accounting for natural phenomena: concepts such as 'space', 'time', 'motion', and 'change'. Scientific physics seeks to establish and explain the phenomena themselves, not by a priori reasoning or conceptual analysis, but by observation, experiment, and hypothesis. The two disciplines are not in competition, and indeed each needs the other; but it is of prime importance to keep in mind the difference between their goals and methods.
The separation of the two was achieved, in this early modern period, in the course of a battle about the authority of the natural philosophy of Aristotle, which contains elements of both disciplines indiscriminately entwined. That philosophy remained dominant in universities both Catholic and Protestant throughout the period, and its influence undoubtedly acted as a brake on the development of sciences such as mechanics and astronomy. These sciences gathered impetus only to the extent that the Aristotelian yoke was thrown off, and this was due above all to three philosophers who attacked the system from outside the academic mainstream: Galileo, Bacon, and Descartes. Sadly, the liberation of physics was