So much upon the growth of passions. Their continuance and decay come next under consideration. And first, it is a general law of nature, that things sudden in their growth, are equally sudden in their decay. This is commonly the case of anger; and with respect to wonder and surprise, another reason concurs, that their causes are of short duration. Novelty soon degenerates into familiarity; and the unexpectedness of an object, is soon sunk in the pleasure which the object affords us. Fear, which is a passion of greater importance as tending to self-preservation, is often instantaneous, and yet is of equal duration with its cause. Nay it frequently subsists after the cause is removed. In the next place, a passion founded on a peculiar propensity, subsists generally for ever. This is the case of pride, envy, and malice. Objects are never wanting, to inflame the propensity into a passion. Thirdly, it may be laid down as a general law of nature, that every passion ceases upon attaining its ultimate end. To explain this law, we must distinguish betwixt a particular and a general end. I call a particular end what may be accomplished by a single act. A general end, on the contrary, admits acts without number; because it cannot be said that a general end is ever fully accomplished while the object of the passion subsists. Gratitude and revenge are examples of the first kind. The ends they aim at may be accomplished by a single act; and when this act is performed, the passions are necessarily at an end. Love and hatred are examples of the other kind. The desire of doing good or of doing mischief to an individual, is a general end, which admits acts without number, and which seldom is fully accomplished. Therefore these passions have frequently the same duration with their objects.