An obvious corollary from these remarks is, that all _causation_ is an exertion of mind, and is only figuratively applied to matter. It necessarily implies power, will, and action. An efficient cause--we are not speaking now of a mere antecedent--is that which is necessarily followed by the effect, so that, if it were known, the effect might be predicted antecedently to all experience. Cicero describes it with philosophical accuracy. "_Causa ea est, quae id efficit, cujus est causa._ _Non sic causa intelligi debet, ut quod cuique antecedat, id ei causa sit; sed quod cuique_ EFFICIENTER _antecedat. Causis enim efficientibus quamque rem cognitis, posse denique sciri quid futurum esset._" Now, in the world of matter, we discover nothing but antecedents and consequents; the former are the mere signs, not the causes, of the latter; no necessary connection--no connection at all, except sequence in time--can be discerned between them. Consequently, from an examination of the former, we could not determine _a priori_, that they must be followed by the latter, or by any other result whatever. Our knowledge here, if knowledge it can be called, is wholly empirical, or founded on experience. As we have seen, it is absurd to say, that one atom of matter literally _acts_ on another. On the other hand, in the world of mind, we are directly conscious of action, and even of causation. All mental exertion is true action; every determination of the will implies _effort_, or the direction and use of power. The result to be accomplished is preconsidered, or meditated, and therefore is known _a priori_, or before experience; the volition succeeds, which is a true effort, or a power in action; and this, _if the power be sufficient_, is _necessarily_ followed by the effect. Volition is a true cause; but in a finite mind it is not always an _adequate_ cause. If I will to shut my eyes, the effect immediately follows as a necessary consequence. But if I will to stop the beating of my heart, or to move a paralyzed limb, the effect does not follow, because the power exerted is inadequate to the end proposed. The action of the will is still _causative_, but it is _insufficient_.