T 2.2.9.20

I shall just observe, before I leave the present subject, that this phænomenon of the double sympathy, and its tendency to cause love, may contribute to the production of the kindness, which we naturally bear our relations and acquaintance. Custom and relation make us enter deeply into the sentiments of others; and whatever fortune we suppose to attend them, is render'd present to us by the imagination, and operates as if originally our own. We rejoice in their pleasures, and grieve for their sorrows, merely from the force of sympathy. Nothing that concerns them is indifferent to us; and as this correspondence of sentiments is the natural attendant of love, it readily produces that affection.