It is their constant union alone, with which we are acquainted; and it is from the constant union the necessity arises. If objects had nor an uniform and regular conjunction with each other, we should never arrive at any idea of cause and effect; and even after all, the necessity, which enters into that idea, is nothing but a determination of the mind to pass from one object to its usual attendant, and infer the existence of one from that of the other. Here then are two particulars, which we are to consider as essential to necessity, viz, the constant union and the inference of the mind; and wherever we discover these we must acknowledge a necessity. As the actions of matter have no necessity, but what is derived from these circumstances, and it is not by any insight into the essence of bodies we discover their connexion, the absence of this insight, while the union and inference remain, will never, in any case, remove the necessity.