1. Badly understood words are the main hindrance to the discovery of truth. But they need not be, especially in physical science, where the senses, experience, and geometrical reasoning prevail. Reflection on motion led ancient philosophers into opinions about it so absurd that they are almost forgotten and merit no attention. But even the better presentday scientists, in their treatment of motion, employ language too abstract and of doubtful reference--for example, the attraction of gravity, effort, latent forces, and the like--which (...) make otherwise learned writings unintelligible. Hence this essay. (shrink)