The foregoing doctrine concerning the train of perceptions, and the pleasure or pain resulting from that train in different circumstances, will be confirmed by attending to the final cause of these effects. And as I am sensible that the mind, inflamed with speculations of this kind so highly interesting, is beyond measure disposed to conviction, I shall be watchful to admit no argument nor remark but what appears solidly founded. With this caution I proceed to the inquiry. It is occasionally observed above, that persons of a phlegmatic temperament, having a sluggish train of perceptions, are indisposed to action; and that activity constantly accompanies a brisk motion of perceptions. To ascertain this fact, a man need not go abroad for experiments. Reflecting upon things passing in his own mind, he will find, that a brisk circulation of thought constantly prompts him to action; and that he is averse to action when his perceptions languish in their course. But man by nature is formed for action, and he must be active in order to be happy. Nature therefore hath kindly provided against indolence, by annexing pleasure to a moderate course of perceptions, and by making every remarkable retardation painful. A slow course of perceptions is attended with another bad effect. Man in a few capital cases is governed by propensity or instinct; but in matters that admit deliberation and choice, reason is assigned him for a guide. Now, as reasoning requires often a great compass of ideas, their succession ought to be so quick, as readily to furnish every motive that may be necessary for mature deliberation. In a languid succession, motives will often occur after action is commenced, when it is too late to retreat.