It is easy to observe, that the passions, both direct and indirect, are founded on pain and pleasure, and that in order to produce an affection of any kind, it is only requisite to present some good or evil. Upon the removal of pain and pleasure there immediately follows a removal of love and hatred, pride and humility, desire and aversion, and of most of our reflective or secondary impressions.

The impressions, which arise from good and evil most naturally, and with the least preparation are the direct passions of desire and aversion, grief and joy, hope and fear, along with volition. The mind by an original instinct tends to unite itself with the good, and to avoid the evil, though they be conceived merely in idea, and be considered as to exist in any future period of time.

But supposing that there is an immediate impression of pain or pleasure, and that arising from an object related to ourselves or others, this does not prevent the propensity or aversion, with the consequent emotions, but by concurring with certain dormant principles of the human mind, excites the new impressions of pride or humility, love or hatred. That propensity, which unites us to the object, or separates us from it, still continues to operate, but in conjunction with the indirect passions, which arise from a double relation of impressions and ideas.

These indirect passions, being always agreeable or uneasy, give in their turn additional force to the direct passions, and encrease our desire and aversion to the object. Thus a suit of fine cloaths produces pleasure from their beauty; and this pleasure produces the direct passions, or the impressions of volition and desire. Again, when these cloaths are considered as belonging to ourself, the double relation conveys to us the sentiment of pride, which is an indirect passion; and the pleasure, which attends that passion, returns back to the direct affections, and gives new force to our desire or volition, joy or hope.

When good is certain or probable, it produces joy. When evil is in the same situation there arises GRIEF or SORROW.

When either good or evil is uncertain, it gives rise to FEAR or HOPE, according to the degrees of uncertainty on the one side or the other.

DESIRE arises from good considered simply, and AVERSION is derived from evil. The WILL exerts itself, when either the good or the absence of the evil may be attained by any action of the mind or body.

Beside good and evil, or in other words, pain and pleasure, the direct passions frequently arise from a natural impulse or instinct, which is perfectly unaccountable. Of this kind is the desire of punishment to our enemies, and of happiness to our friends; hunger, lust, and a few other bodily appetites. These passions, properly speaking, produce good and evil, and proceed not from them, like the other affections.

None of the direct affections seem to merit our particular attention, except hope and fear, which we shall here endeavour to account for. It is evident that the very same event, which by its certainty would produce grief or joy, gives always rise to fear or hope, when only probable and uncertain. In order, therefore, to understand the reason why this circumstance makes such a considerable difference, we must reflect on what I have already advanced in the preceding book concerning the nature of probability.

Probability arises from an opposition of contrary chances or causes, by which the mind is not allowed to fix on either side, but is incessantly tost from one to another, and at one moment is determined to consider an object as existent, and at another moment as the contrary. The imagination or understanding, call it which you please, fluctuates betwixt the opposite views; and though perhaps it may be oftener turned to the one side than the other, it is impossible for it, by reason of the opposition of causes or chances, to rest on either. The pro and con of the question alternately prevail; and the mind, surveying the object in its opposite principles, finds such a contrariety as utterly destroys all certainty and established opinion.

Suppose, then, that the object, concerning whose reality we are doubtful, is an object either of desire or aversion, it is evident, that, according as the mind turns itself either to the one side or the other, it must feel a momentary impression of joy or sorrow. An object, whose existence we desire, gives satisfaction, when we reflect on those causes, which produce it; and for the same reason excites grief or uneasiness from the opposite consideration: So that as the understanding, in all probable questions, is divided betwixt the contrary points of view, the affections must in the same manner be divided betwixt opposite emotions.

Now if we consider the human mind, we shall find, that with regard to the passions, it is not 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 extreme 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. It is observable, that where the objects of contrary passions are presented at once, beside the encrease 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 law-suit, 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 tranquility.

But suppose, in the third place, that the object is not a compound of good or evil, but is considered as probable or improbable in any degree; in that case I assert, that the contrary passions will both of them be present at once in the soul, and instead of destroying and tempering each other, will subsist together, and produce a third impression or affection by their union. Contrary passions are not capable of destroying each other, except when their contrary movements exactly rencounter, and are opposite in their direction, as well as in the sensation they produce. This exact rencounter depends upon the relations of those ideas, from which they are derived, and is more or less perfect, according to the degrees of the relation. In the case of probability the contrary chances are so far related, that they determine concerning the existence or non-existence of the same object. But this relation is far from being perfect; since some of the chances lie on the side of existence, and others on that of non-existence; which are objects altogether incompatible.

It is impossible by one steady view to survey the opposite chances, and the events dependent on them; but it is necessary, that the imagination should run alternately from the one to the other. Each view of the imagination produces its peculiar passion, which decays away by degrees, and is followed by a sensible vibration after the stroke. The incompatibility of the views keeps the passions from shocking in a direct line, if that expression may be allowed; and yet their relation is sufficient to mingle their fainter emotions. It is after this manner that hope and fear arise from the different mixture of these opposite passions of grief and joy, and from their imperfect union and conjunction.

Upon the whole, contrary passions succeed each other alternately, when they arise from different objects: They mutually destroy each other, when they proceed from different parts of the same: And they subsist both of them and mingle together, when they are derived from the contrary and incompatible chances or possibilities, on which any one object depends. The influence of the relations of ideas is plainly seen in this whole affair. If the objects of the contrary passions be totally different, the passions are like two opposite liquors in different bottles, which have no influence on each other. If the objects be intimately connected, the passions are like an alcali and an acid, which, being mingled, destroy each other. If the relation be more imperfect, and consists in the contradictory views of the same object, the passions are like oil and vinegar, which, however mingled, never perfectly unite and incorporate.

As the hypothesis concerning hope and fear carries its own evidence along with it, we shall be the more concise in our proofs. A few strong arguments are better than many weak ones.

The passions of fear and hope may arise when the chances are equal on both sides, and no superiority can be discovered in the one above the other. Nay, in this situation the passions are rather the strongest, as the mind has then the least foundation to rest upon, and is tossed with the greatest uncertainty. Throw in a superior degree of probability to the side of grief, you immediately see that passion diffuse itself over the composition, and tincture it into fear. Encrease the probability, and by that means the grief, the fear prevails still more and more, till at last it runs insensibly, as the joy continually diminishes, into pure grief. After you have brought it to this situation, diminish the grief, after the same manner that you encreased it; by diminishing the probability on that side, and you'll see the passion clear every moment, until it changes insensibly into hope; which again runs, after the same manner, by slow degrees, into joy, as you encrease that part of the composition by the encrease of the probability.