Now, if we consider the human mind, we shall find, that, with regard to the passions, 'tis not of the nature of a wind-instrument of music, which, in running over all the notes, immediately loses the sound after the breath ceases; but rather resembles, a string-instrument, where, after each stroke, the vibrations still retain some sound, which gradually and insensibly decays. The imagination is extremely quick and agile; but the passions are slow and restive: for which reason, when any object is presented that affords a variety of views to the one, and emotions to the other, though the fancy may change its views with great celerity, each stroke will not produce a clear and distinct note of passion, but the one passion will always be mixt and confounded with the other. According as the probability inclines to good or evil, the passion of joy or sorrow predominates in the composition: because the nature of probability is to cast a superior number of views or chances on one side; or, which is the same thing, a superior number of returns of one passion; or, since the dispersed passions are collected into one, a superior degree of that passion. That is, in other words, the grief and joy being intermingled with each other, by means of the contrary views of the imagination, produce, by their union, the passions of hope and fear. Upon this head there may be started a very curious question concerning that contrariety of passions which is our present subject. 'Tis observable, that where the objects of contrary passions are presented at once, beside the increase of the predominant passion (which has been already explained, and commonly arises at their first shock or rencounter), it sometimes happens that both the passions exist successively, and by short intervals; sometimes, that they destroy each other, and neither of them takes place; and sometimes that both of them remain united in the mind. It may therefore be asked, by what theory we can explain these variations, and to what general principle we can reduce them. When the contrary passions arise from objects entirely different, they take place alternately, the want of relation in the ideas separating the impressions from each other, and preventing their opposition. Thus, when a man is afflicted for the loss of a lawsuit, and joyful for the birth of a son, the mind running from the agreeable to the calamitous object, with whatever celerity it may perform this motion, can scarcely temper the one affection with the other, and remain betwixt them in a state of indifference. It more easily attains that calm situation, when the same event is of a mixt nature, and contains something adverse and something prosperous in its different circumstances. For in that case, both the passions, mingling with each other by means of the relation, become mutually destructive, and leave the mind in perfect tranquillity.