 It is in this way that Galileo developed the categories of the mechanical new science, the science of matter and motion. His new categories utilized some of the basic principles of traditional mechanics, to which he added the category of time and so emphasized acceleration. But throughout, he was working out the details about the nature of matter so that it could be understood as uniform and universal, and treated in a way that allowed for coherent discussion of the principles of motion. It was due to Galileo that a unified matter became accepted and its nature became one of the problems for the new science that followed. After him, matter really mattered.