Every object is determined by an absolute fate toa certain degree and direction of irs motion, and can no more depart from that precise line, in which it moves, than it can convert itself into an angel, or spirit, or any superior substance.

The actions, therefore, of matter are to be regarded as instances of necessary actions; and whatever is in this respect on the same footing with matter, must be acknowledged to be necessary.

That we may know whether this be the case with the actions of the mind, we shall begin with examining matter, and considering on what the idea of a necessity in its operations are founded, and why we conclude one body or action to be the infallible cause of another.
It has been observed 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.

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.