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 in many instances, is observed to encrease its violence, beyond the pitch, at which it would have arrived, had it met with no opposition. Hence we naturally desire what is forbid, and often take a pleasure in performing actions, merely because they are unlawful. The notion of duty, when opposite to the passions, is not always able to overcome them; and when it fails of that influence, is apt rather to encrease and irritate them, by producing an opposition in our motives and principles.
4. The same effect follows, whether the opposition arises from internal motives or external obstacles. The passion commonly acquires new force in both cases. The efforts, which the mind makes to surmount the obstacle, excite the spirits, and enliven the passion.
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