The method of scientific investigation that became prevalent in the seventeenth century rests on the assumption that the universe can be understood on the analogy of a machine rather than on that of an organism. On this view, the basic explanatory elements are matter and motion, where matter is characterized by size and shape, and motion is described by a small number of rules based on the principle of inertia. This mechanical philosophy, as it came to be known, was considered the simplest, as well as the most economical and comprehensive of all possible accounts of nature. With Galileo and Newton it triumphed not only in mechanics but also in cosmology and, with Descartes, in the reduction of the phenomena of life to the working of a clock.