If I diminish the vivacity of the first conception, I diminish that of the related ideas; as pipes can convey no more water than what arises at the fountain.

By this diminution I destroy the future prospect, which is necessary to interest me perfectly in the fortune of another.

I may feel the present impression, but carry my sympathy no farther, and never transfuse the force of the first conception into my ideas of the related objects.

If it be another's misery, which is presented in this feeble manner, I receive it by communication, and am affected with all the passions related to it: But as I am not so much interested as to concern myself in his good fortune, as well as his bad, I never feel the extensive sympathy, nor the passions related to it.
Now in order to know what passions are related to these different kinds of sympathy, we must consider, that benevolence is an original pleasure arising from the pleasure of the person beloved, and a pain proceeding from his pain: From which correspondence of impressions there arises a subsequent desire of his pleasure, and aversion to his pain.

In order, then, to make a passion run parallel with benevolence, it is requisite we should feel these double impressions, correspondent to those of the person, whom we consider; nor is any one of them alone sufficient for that purpose.