moment. The forms or ideas of a Plato or an Aristotle correspond to privileged or salient moments in the history of things—the very same moments, generally speaking, that have been fixed by language. They are supposed, like the infancy and old age of a living being, to characterize and express the quintessence of a period, all the remainder of which is filled with the transition from one state to another, and is, therefore, devoid of interest in itself. Consider, for example, the falling of a body. It was thought to be a sufficient account of the fact when it had been characterized summarily as a movement downward, a tendency towards a center, the natural movement of a body, which, after being separated from the earth to which it belongs, returns again to its original position. Therefore, the final or culminating point (Τέλος άκμή) of a process is singled out and is erected into an essential moment, and science is satisfied with this moment, which language has seized upon for the purpose of expressing the ensemble of the fact. In the physics of Aristotle, the movement of a body hurled through space, or freely falling, is defined by concepts of above and below, of spontaneous and enforced displacement, of proper and improper position. But Gallilei believed that there was no essential moment, no privileged instant; in his opinion one should be able to give an account of a falling body at any moment in its course, for that is the true science of gravitation which determines the position of a body in space at any instant of time. For this purpose we, of course, need more precise symbols than those of language.^[1]