Motion; or the Principle and Nature of Motion, and the Cause of the Communication of Motions 1721

1 In order to discover the truth, it is most important that one avoid being obstructed by words that are poorly understood. While almost all philosophers give this advice, few observe it. Indeed, it hardly seems so difficult to do so, especially in matters that are discussed by physicists, in which sensation, experience, and geometrical reasoning are appropriate. Accordingly, having set aside as much as possible all prejudices that result either from common ways of speaking or from the authority of philosophers, one should examine diligently the very nature of things. Nor should the authority of anyone be valued to such an extent that their words and terms are prized even when nothing clear and certain can be found in them.

2 The consideration of motion troubled the minds of ancient philosophers very much; their thinking gave rise to a range of views which were extraordinarily difficult (not to say absurd) and which, since they have now lapsed almost into desuetude, hardly deserve that we devote much effort to discussing them. However, among the more recent and more sensible philosophers of the current period, when they discuss motion, one finds many words whose meaning is too abstract and obscure, such as the ‘solicitation of gravity’, ‘striving’, ‘dead forces’, etc.