But the case is very different when we turn from the contemplation of a _passive result_ to consider an _efficient cause_--when we turn from the _motion of body_ to consider the _activity of mind_. In such a case, the consequent ceases to be the same; and hence we have no right to infer that the antecedent is the same. We are conscious of an act; we perceive that it is followed by a change in the outward world; and henceforth, whenever we observe another change in the outward world, we are compelled to ascribe it, also, to a similar cause. This conviction results from the constitution of our minds--from a fundamental law of belief. But when we contemplate, not a change in the outward world, in that which is passive, but an act of the mind itself, the case is entirely different. We have some experience that certain changes in matter are the results of certain acts; and hence, whenever we observe similar phenomena, we are under a necessity of our nature to refer them to similar causes. We merely rely upon our veritable belief in the uniformity of nature's sequences, without a reliance upon which there can be no such thing as reasoning, when we ascend from the changes in the outward world to a belief in the agency of an efficient Cause. But we have no experience that an act of the mind is produced by a preceding act of the mind, or by the prior action of any thing else. President Edwards himself admits that our experience is silent on this subject. And hence, when we witness an act of the mind, or when we are conscious of a volition, our instinctive belief in the uniformity of nature's sequences does not require us to believe that it has an efficient cause; or, in other words, that it is produced by the prior action of something else, as the motion of body is produced by a prior act of mind. _A change in body_ necessarily implies the prior action of something else by which it is produced; _an act of mind_ only implies the existence of an agent that is capable of acting. Wherever an act exists, we must believe that there is a soul, or mind, or agent, that is capable of acting. We need not suppose that, like a change in body, it is brought to pass by a prior act. In other words, a change in that which is by nature passive, necessarily implies an act by which it is produced. But an act of the mind itself, which is not passive, does not likewise imply a preceding act by which it is produced. _It only implies the existence of an agent that is capable of acting, and the circumstances necessary to action as conditions, not as causes._