The harm and the justice are two contrary objects, of which the one has a tendency to produce hatred, and the other love; and it is according to their different degrees, and our particular turn of thinking, that either of the objects prevails, and excites its proper passion.
SECT.

IV OF THE LOVE OF RELATIONS Having given a reason, why several actions, that cause a real pleasure or uneasiness, excite not any degree, or but a small one, of the passion of love or hatred towards the actors; it will be necessary to shew, wherein consists the pleasure or uneasiness of many objects, which we find by experience to produce these passions.
According to the preceding system there is always required a double relation of impressions and ideas betwixt the cause and effect, in order to produce either love or hatred.

But though this be universally true, it is remarkable that the passion of love may be excited by only one relation of a different kind, viz, betwixt ourselves and the object; or more properly speaking, that this relation is always attended with both the others.

Whoever is united to us by any connexion is always sure of a share of our love, proportioned to the connexion, without enquiring into his other qualities.

Thus the relation of blood produces the strongest tie the mind is capable of in the love of parents to their children, and a lesser degree of the same affection, as the relation lessens.