Thus, then, Hume considers that, by an inductive determination, on the strict Newtonian basis, he has proved that the SOLE foundation of our regard to justice is the support and welfare of society:  and since no moral excellence is more esteemed, we must have some strong disposition in favour of general usefulness.  Such a disposition must be a part of the humane virtues, as it is the SOLE source of the moral approbation of fidelity, justice, veracity, and integrity.

Section IV. relates to POLITICAL SOCIETY, and is intended to show that Government, Allegiance, and the Laws of each State, are justified solely by Utility.

If men had sagacity to perceive, and strength of mind to follow out, distant and general interests, there had been no such thing as government.  In other words, if government were totally useless, it would not be.  The duty of Allegiance would be no duty, but for the advantage of it, in preserving peace and order among mankind.

[Hume is here supposing that men enter into society on equal terms; he makes no allowance for the exercise of the right of the stronger in making compulsory social unions.  This, however, does not affect his reasoning as to the source of our approbation of social duty, which is not usually extended to tyranny.]

When political societies hold intercourse with one another, certain regulations are made, termed Laws of Nations, which have no other end than the advantage of those concerned.

The virtue of Chastity is subservient to the utility of rearing the young, which requires the combination of both parents; and that combination reposes on marital fidelity.  Without such a utility, the virtue would never have been thought of.  The reason why chastity is extended to cases where child-bearing does not enter, is that general rules are often carried beyond their original occasion, especially in matters of taste and sentiment.

The prohibition of marriage between near relations, and the turpitude of incest, have in view the preserving of purity of manners among persons much together.

The laws of good manners are a kind of lesser morality, for the better securing of our pleasures in society.

Even robbers and pirates must have their laws.  Immoral gallantries, where authorized, are governed by a set of rules.  Societies for play have laws for the conduct of the game.  War has its laws as well as peace.  The fights of boxers, wrestlers, and such like, are subject to rules.  For all such cases, the common interest and utility begets a standard of right and wrong in those concerned.

Section V. proceeds to argue WHY UTILITY PLEASES.  However powerful education may be in forming men’s sentiments, there must, in such a matter as morality, be some deep natural distinction to work upon.  Now, there are only two natural sentiments that Utility can appeal to:  (1) Self-Interest, and (2) Generosity, or the interests of others.