T 2.3.1.4

It has been observ'd already, that in no single instance the ultimate connexion of any objects is discoverable, either by our senses or reason, and that we can never penetrate so far into the essence and construction of bodies, as to perceive the principle, on which their mutual influence depends. 'Tis their constant union alone, with which we are acquainted; and 'tis from the constant union the necessity arises. If objects had not an uniform and regular conjunction with each other, we shou'd 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 deriv'd 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. 'Tis the observation of the union, which produces the inference; for which reason it might be thought sufficient, if we prove a constant |union in the actions of the mind, in order to establish the inference, along with the necessity of these actions. But that I may bestow a greater force on my reasoning, I shall examine these particulars apart, and shall first prove from experience, that our actions have a constant union with our motives, tempers, and circumstances, before I consider the inferences we draw from it.