Thus moral sense and sympathy jointly, as understood by Hume, serve plausibly to explain the office ordinarily ascribed to conscience, as the judge and possible controller in each man of his own acts. At the same time the lines are indicated along which a physical theory of conscience might be logically attempted. The problem which Hume bequeathed to a successor who adopted his principles was mainly to account for the twofold fact, that the mere survey of actions as tending to produce pleasures in which the contemplator will have no share, is yet a source of pleasure to him; and that, among the pleasures taken into account in that estimate of the tendency of an action which determines the moral sentiment, are such as have no direct connexion with the satisfaction of animal wants. A theory which will account for this will also account for the affection of the agent by sympathy with the sentiment which the contemplation of his action excites in others. Can we find any scientific warrant for believing in a process by which, out of susceptibility to pleasure incidental to the merely animal life, there have grown those capacities for enjoyment which we consider essential to general well-being, and those social interests which not only make the contemplation of general well-being an independent source of pleasure, but also make the pleasure of exciting this pleasure—the pleasure of satisfying the moral sentiment of others—an object of desire so strong as in many cases to determine action? If we can, it would seem that we have given to our national system of ethics—the ethics of moral sentiment—the solid foundation of a natural science. (§4 ¶1)