Since passions, however independent, are naturally transfus'd into each other, if they are both present at the same time; it follows, that when good or evil is plac'd in such a situation, as to cause any particular emotion, beside its direct passion of desire or aversion, that latter passion must acquire new force and violence.
This happens, among other cases, whenever any object excites contrary passions. For 'tis observable that an opposition of passions commonly causes a new emotion in the spirits, and produces more disorder, than the concurrence of any two affections of equal force. This new emotion is easily converted into the predominant passion, and en creases its violence, beyond the pitch it wou'd have arriv'd at had it met with no opposition. Hence we naturally desire what is forbid, and take a pleasure in performing actions, merely because they are unlawful. The notion of duty, when opposite to the passions, is seldom able to overcome them; and when it fails of that effect, is apt rather to encrease them, by producing an opposition in our motives and principles.
The same effect follows whether the opposition arises from internal motives or external obstacles. The passion commonly acquires new force and violence in both cases. The efforts, which the mind makes to surmount the obstacle, excite the spirits and inliven the passion.
Uncertainty has the same influence as opposition. The agitation of the thought; the quick turns it makes from one view to another; the variety of passions, which succeed each other, according to the different views: All these produce an agitation in the mind, and transfuse themselves into the predominant passion.
There is not in my opinion any other natural cause, why security diminishes the passions, than because it removes that uncertainty, which encreases them. The mind, when left to itself, immediately languishes; and in order to preserve its ardour, must be every moment supported by a new flow of
