As the transition of ideas is here made contrary to the natural propensity of the imagination, that faculty must be overpowered by some stronger principle of another kind; and as there is nothing ever present to the mind but impressions and ideas, this principle must necessarily lie in the impressions.  Now it has been observed, that impressions or passions are connected only by their resemblance, and that where any two passions place the mind in the same or in similar dispositions, it very naturally passes from the one to the other:  As on the contrary, a repugnance in the dispositions produces a difficulty in the transition of the passions.  But it is observable, that this repugnance may arise from a difference of degree as well as of kind; nor do we experience a greater difficulty in passing suddenly from a small degree of love to a small degree of hatred, than from a small to a great degree of either of these affections.  A man, when calm or only moderately agitated, is so different, in every respect, from himself, when disturbed with a violent passion, that no two persons can be more unlike; nor is it easy to pass from the one extreme to the other, without a considerable interval betwixt them.

The difficulty is not less, if it be not rather greater, in passing from the strong passion to the weak, than in passing from the weak to the strong, provided the one passion upon its appearance destroys the other, and they do not both of them exist at once.  But the case is entirely altered, when the passions unite together, and actuate the mind at the same time.  A weak passion, when added to a strong, makes not so considerable a change in the disposition, as a strong when added to a weak; for which reason there is a closer connexion betwixt the great degree and the small, than betwixt the small degree and the great.

The degree of any passion depends upon the nature of its object; and an affection directed to a person, who is considerable in our eyes, fills and possesses the mind much more than one, which has for its object a person we esteem of less consequence.  Here then the contradiction betwixt the propensities of the imagination and passion displays itself.  When we turn our thought to a great and a small object, the imagination finds more facility in passing from the small to the great, than from the great to the small; but the affections find a greater difficulty:  And as the affections are a more powerful principle than the imagination, no wonder they prevail over it, and draw the mind to their side.  In spite of the difficulty of passing from the idea of great to that of little, a passion directed to the former, produces always a similar passion towards the latter; when the great and little are related together.  The idea of the servant conveys our thought most readily to the master; but the hatred or love of the master produces with greater facility anger or good-will to the servant.  The strongest passion in this case takes the precedence; and the addition of the weaker making no considerable change on the disposition, the passage is by that means rendered more easy and natural betwixt them.