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.