every Effect is so precisely determin'd by the Nature and Energy of its Cause, that no other Effect, in such particular Circumstances, could possibly have resulted from the Operation of that Cause. The Degree and Direction of every Motion is, by the Laws of Nature, prescrib'd with such Exactness, that a living Creature may as soon arise from the Shock of two Bodies, as Motion in any other Degree or Direction, than what is actually produc'd by it. Would we, therefore, form a just and precise Idea of Necessity, we must consider, whence that Idea arises, when we apply it to the Operation of Bodies.
It seems evident, that, if all the Scenes of Nature were shifted continually in such a Manner, that no two Events bore any Resemblance to each other, but every Object was entirely new, without any Similitude to whatever had been seen before, we should never, in that Case, have attain'd the least Idea of Necessity, or of a Connexion amongst these Objects. We might say, upon such a Supposition, that one Object or Event has follow'd another; not that one was produc'd by the other. The Relation of Cause and Effect must be utterly unknown to Mankind. Inference and Reasoning concerning the Operations of Nature would, from that Moment, be at an End; and the Memory and Senses remain the only Canals, by which the Knowledge of any real Existence could possibly have access to the Mind. Our Idea, therefore, of Neces-sity
