T 2.2.2.16

Now I have observ'd, that those two faculties of the mind, the imagination and passions, assist each other in their operation, when their propensities are similar, and when they act upon the same object. The mind has always a propensity to pass from a passion to any other related to it; and this propensity is forwarded when the object of the one passion is related to that of the other. The two impulses concur with each other, and render the whole transition more smooth and easy. But if it shou'd happen, that while |the relation of ideas, strictly speaking, continues the same, its influence, in causing a transition of the imagination, shou'd no longer take place, 'tis evident its influence on the passions must also cease, as being dependent entirely on that transition. This is the reason why pride or humility is not transfus'd into love or hatred with the same ease, that the latter passions are chang'd into the former. If a person be my brother I am his likewise: But tho' the relations be reciprocal, they have very different effects on the imagination. The passage is smooth and open from the consideration of any person related to us to that of ourself, of whom we are every moment conscious. But when the affections are once directed to ourself, the fancy passes not with the same facility from that object to any other person, how closely so ever connected with us. This easy or difficult transition of the imagination operates upon the passions, and facilitates or retards their transition; which is a clear proof, that these two faculties of the passions and imagination are connected together, and that the relations of ideas have an influence upon the affections. Besides innumerable experiments that prove this, we here find, that even when the relation remains; if by any particular circumstance its usual effect upon the fancy in producing an association or transition of ideas, is prevented; its usual effect upon the passions, in conveying us from one to another, is in like manner prevented.