Justice, according to Hume, is an artificial virtue, which springs from the difficulties that scarcity presents. Justice here is related to property rights. He notes that where there is no scarcity of goods (for example water and air), there are consequently no disputes, since they are easily accessible by all in abundance. And, as he further points out, land in some country is also viewed this way—it being so plentiful that no rules are really necessary. But Hume takes it as self-evident that there will be conflict over scarce resources. If the majority of land is occupied, my use of this land precludes the use of this land by another, and these others might be motivated to dispossess me of this land.
His solution is not to abolish the institution of private property, as private property is far too ingrained. Nor would we want to, for there are tremendous benefits to be gained from decentralizing resources into the hands of the industrious. Where there is no scarcity, justice is of no use at all. Its primary use is that of utility; but Hume readily acknowledges that if it ceases to perform its function and wealth becomes centralized enough so that a minority of the population has all the wealth, he argues that justice can easily be discarded because it does not have the same status, as say, a natural law would. It is useful for certain ends, and if it cannot fulfill its function, it is suspended until later needed.
Hume further illustrates his understanding of justice through an example of a war between barbarians and a civilized nation. Justice in this case can readily be abandoned, since the war begins precisely because both cultures have incompatible notions of justice. If the barbarians do not observe the rules of war, there is no reason why the civilized nation should hold its head high and accept the casualties. The rules of justice serve no purpose here. That justice is useful to society is self-evident, but the real question is whether its beneficial consequences can be the sole foundation. Hume intends to argue for this radically reductionist account of justice, which he distinguishes from the natural virtues.
The natural virtues arise out of the disposition of men towards one another. While Hume’s account is agent-centered and mildly egoistic, it is a far cry from Hobbes’ crude oversimplification of selfish desire as being the ultimate reason for action. Hume criticizes this heavily for being naïve; clearly there are other motivating factors at play. Hume labels these the sentiments. We can have benevolent sentiments, altruistic ones, kind sentiments, etc. We are free to name them as they appear without constantly having to reduce them to raw egoism. While Hume does admit that there is a possibility that egoism may be the only true foundation of action, he does not think it very likely, and argues strongly for a more thick conception of human action.
There is nothing more than this, however. The sentiments do not lead us to facts of the matter about morality. Morality is one of those concepts that must go the way of most metaphysics, according to Hume. His Epicurean materialism will not let it in the door. His first assault on the notion of objective morality is that reason is impotent in guiding us to action; it is cold and dispassionate. But, Hume says, we are clearly motivated to act in ways which we think are moral. So, he concludes, their basis cannot be rational. In the Inquiry, Hume softens his original approach in the Treatise, admitting that reason does play a part, albeit a small one. It is still for the most part a slave to the passions, to be used to rationalize our actions. These actions cannot really be called reasonable or unreasonable, but are merely laudable or unlaudable.
The second attack on morality comes from the is/ought problem. All the moral systems, which he had previously analyzed, all made heavy use of factual premises to lead to moral conclusions. But, Hume says, that is a formal deductive fallacy. One cannot infer something that was not first in the premises, and since statements of fact have no normative content, it follows that the majority of moral systems have been taken by Hume and dashed on the rocks. Although he agrees with Aristotle on his emphasis on character, Hume’s account differs because it is non-cognitive, a term that would later by heavily used by Ayer and the logical positivists to demonstrate that since morality is neither analytic nor synthetic, it must be based purely on emotions, and any claim beyond that is merely illusory.