IN the last section I considered the application of the maxim, "that every effect must have a cause," to the question of necessity. This maxim figures so largely in every scheme of necessity, and it is relied upon with so much confidence, that I shall present some further views respecting its true nature and application. The necessitarian may see the truth of this maxim clearly, but he applies it vaguely. He is always saying, "that if we give up this great principle of common sense, then there is no reasoning from effect to cause; and we cannot prove the existence of a God." Now I propose to show that we need not give up "this great principle of common sense;" that we may continue to reason from effect to cause, and so reach the conclusion that there is a God, by one of the most incontrovertible of all our mental processes; and yet we may, with perfect consistency, refuse to apply the maxim in question to human actions or volitions. In other words, that we may freely admit the principle in question, and yet reject the application which the necessitarian is accustomed to make of it. In order to do this in a perspicuous and satisfactory manner, let us consider the occasion on which we first became acquainted with the truth of the principle, that every effect must have a cause. Let us consider the circumstances under which it is first suggested to the mind. Whence, then, do we derive the ideas of cause and effect, and of the necessary connection between them? Locke, it is well known, supposed that we might derive the idea of causation by reflecting on the changes which take place in the external world. The fallacy of this supposition has been fully shown by Hume, and Brown, and Consin. In the refutation of Locke's notion, these celebrated philosophers were undoubtedly right; but the two first were wrong in the conclusion that we have no idea of power at all. Because the ideas of power and causation are not suggested by the changes of the material world, it does not follow that we have no such ideas in reality; that the only notion we have of causation is that of an invariable antecedence. The only way in which the mind ever comes to be furnished with the ideas of cause and effect at all is this: we are conscious that we will a certain motion in the body, and we discover that the motion follows the volition. It is this act of the mind, this exertion of the will, that gives us the idea of a cause; and the change which it produces in the body, is that from which we derive the idea of an effect. If we had never experienced a volition, we should never have formed the idea of causation. The idea of positive efficiency, or active power, would never have entered into our minds.