Self-love is a principle in human nature of such extensive energy, and the interest of each individual is, in general, so closely connected with that of the community, that those philosophers were excusable, who fancied that all our concern for the public might be resolved into a concern for our own happiness and preservation.

They saw every moment, instances of approbation or blame, satisfaction or displeasure towards characters and actions; they denominated the objects of these sentiments, VIRTUES, or VICES; they observed, that the former had a tendency to increase the happiness, and the latter the misery of mankind; they asked, whether it were possible that we could have any general concern for society, or any disinterested resentment of the welfare or injury of others; they found it simpler to consider all these sentiments as modifications of self-love; and they discovered a pretence, at least, for this unity of principle, in that close union of interest, which is so observable between the public and each individual.
But notwithstanding this frequent confusion of interests, it is easy to attain what natural philosophers, after Lord Bacon, have affected to call the experimentum crucis, or that experiment which points out the right way in any doubt or ambiguity.

We have found instances, in which private interest was separate from public; in which it was even contrary: And yet we observed the moral sentiment to continue, notwithstanding this disjunction of interests.

And wherever these distinct interests sensibly concurred, we always found a sensible increase of the sentiment, and a more warm affection to virtue, and detestation of vice, or what we properly call, GRATITUDE and REVENGE.
Compelled by these instances, we must renounce the theory, which accounts for every moral sentiment by the principle of self-love.

We must adopt a more public affection, and allow, that the interests of society are not, even on their own account, entirely indifferent to us.