In Thucydides's History of the Peloponnesian War, the rhetorical orations of ancient Greek statesmen often alternated between appealing to honor and to interest: to justice and to expediency.
Similarly, modern classical liberals (libertarians) often take a dual approach to making the case for liberty.
On one hand they put forth arguments that can be characterized as "economic," "pragmatic," "consequentialist," or "utilitarian." For example, when making the case against price ceilings, a libertarian acquainted with economics may point out that such a policy would result in shortages.
On the other hand they put forth arguments that can be characterized as "moral," "ethical," "principled," or "deontological." For example, a libertarian may object to price ceilings on the grounds that such a policy would simply constitute aggression against sellers who would like to charge prices above the ceiling.
The libertarian who uses both approaches will argue from two different sets of grounds to arrive at the same conclusion. Many libertarians simply welcome the thought that their rhetorical armory has two expansive wings, and pay little regard to if and how the two wings are connected. But when two different approaches to a question happen to arrive at the same answer, the hand tends to drift toward Ockham's razor. The suspicion arises that one approach can ultimately be resolved into the other.
Characterizing the deontological approach as the "moral" one can be misleading. It can make it seem as if those who exclusively take the utilitarian approach are somehow "antimorality." But that is not the case. Utilitarians consider morality to be essential. The two approaches simply operate under different conceptions of what morality is.
Morality has to do with codes of interpersonal conduct. When a libertarian says, "X should be refrained from because it is immoral, or constitutes aggression (initiation of force), or is a violation of property rights, etc.," they are ultimately saying, "X should be refrained from because it is contrary to a given code of interpersonal conduct."
Deontological libertarians often treat their favored code of interpersonal conduct to be somehow natural, perennial, divine, or absolute in some other way.
Utilitarian liberals recognize that all codes of conduct are "artificial" in that they are man-madethings. Ludwig von Mises, the greatest utilitarian liberal, wrote,
There is, however, no such thing as a perennial standard of what is just and what is unjust. Nature is alien to the idea of right and wrong.… The notion of right and wrong is a human device.
Furthermore, all things made by men are made for a purpose, and the only standard by which a man-made thing can be judged is according to how well it fulfills the purpose for which it was made. Again, Mises:
All moral rules and human laws are means for the realization of definite ends. There is no method available for the appreciation of their goodness or badness other than to scrutinize their usefulness for the attainment of the ends chosen and aimed at.
So when a libertarian says something tantamount to, "X should be refrained from because it is contrary to a given code of interpersonal conduct," that only raises the question, Why should this code of interpersonal conduct be adopted, and not others?
To answer, "because it is the only code of interpersonal conduct that is moral" would be untenable. It would be tantamount to saying, "because it is the only code of interpersonal conduct that is consistent with some second code of conduct"; and this only leads to an infinite regress. Why should the second code of conduct, according to which the first code of conduct is judged, be adopted? Because of a third code of conduct?
The only escape from this infinite regress is to recognize that, as pointed out by Mises above, codes of interpersonal conduct are ultimately adopted by acting individuals for a purpose. And that purpose is the facilitation of social cooperation, which, because of the greater productivity of the division of labor, is the foremost means to nearly everyone's ends. In a passage he called "The Utilitarian Doctrine Restated," Mises wrote,
Human effort exerted under the principle of the division of labor in social cooperation achieves, other things remaining equal, a greater output per unit of input than the isolated efforts of solitary individuals. Man's reason is capable of recognizing this fact and of adapting his conduct accordingly. Thus social cooperation becomes for almost every man the great means for the attainment of all ends. An eminently human common interest, the preservation and intensification of social bonds, is substituted for pitiless biological competition, the significant mark of animal and plant life. Man becomes a social being.
The fact that social cooperation is "the great means for the attainment of all ends" leads to important conclusion. Libertarians who, following Murray Rothbard, search for an "objective ethic" argue that utilitarian and economic arguments regarding the suitability of means are insufficient for making the case for liberty. They claim that ethical arguments regarding which ultimate ends oneought to have are necessary. Mises rejects this, because
As social cooperation is for acting man a means and not an end, no unanimity with regard to value judgments is required to make it work.… With the exception of the small, almost negligible number of consistent anchorites, all people agree in considering some kind of social cooperation between men the foremost means to attain any ends they may aim at. This undeniable fact provides a common ground on which political discussions between men become possible.
The following objection may be raised. Why is the greater productivity of the division of labor such a big deal that it makes social cooperation the foremost means to all our ends? Is that not crass materialism? For many, are not spiritual ends more important than brute "productivity"? Mises answered this objection as follows:
It is a fact that almost all men agree in aiming at certain ends, at those pleasures which ivory-tower moralists disdain as base and shabby. But it is no less a fact that even the most sublime ends cannot be sought by people who have not first satisfied the wants of their animal body. The loftiest exploits of philosophy, art, and literature would never have been performed by men living outside of society.
Or as Phillip Wicksteed pithily put it,
In fact, a man can be neither a saint, nor a lover, nor a poet, unless he has comparatively recently had something to eat.
The utility of social cooperation is paramount for virtually all acting men, and it is the very foundation of morality.
The notion of right and wrong is … a utilitarian precept designed to make social cooperation under the division of labor possible.
And as the foundation of all morality in general, the utility of social cooperation is also the alpha and the omega of all questions of justice and property in particular.
The ultimate yardstick of justice is conduciveness to the preservation of social cooperation. Conduct suited to preserve social cooperation is just, conduct detrimental to the preservation of society is unjust. There cannot be any question of organizing society according to the postulates of an arbitrary preconceived idea of justice. The problem is to organize society for the best possible realization of those ends which men want to attain by social cooperation. Social utility is the only standard of justice.
People develop the custom of abiding by general rules (including the rules of justice) because of a general recognition that when both the long-run and short-run are taken into account, any given individual is likely to be better off, according to his own preferences, with the rules, than without them.
The general expediency of certain codes of conduct are recognized by thought leaders in society. These thought leaders convince others, who in turn convince still others. Over time, and as codes of conduct are passed across generations and intellectual strata, consciously formulated customs gradually evolve into blindly imbibed folkways.
Moral standards are initially adopted to please one's parents, peers, or divinity; then as adherence to them becomes habitual through repetition, they are internalized as one's own conscience. This internalization can become so complete that people can come to think of their moral standards as facts of nature, and not as human devices; philosophically minded people will even attempt to concoct rationalizations for this conclusion.
Some moral traditions can take on a life of their own, and become quasi ends in themselves. For the sake of their transmission and perpetuation, they can also be buttressed by divine or metaphysical pronouncements, and adorned by ritual. But ultimately all customs are human means, not divine or ultimate ends in themselves. And if a general awareness of the relative inexpediency of a custom arises, this will erode the utilitarian basis of its social acceptance, and it will eventually topple.
Before the advent of economic science, society's thought leaders were groping around in the dimness of mankind's lengthy intellectual dawn. They were able to glean a few basic principles of social expediency. Foremost of these is that everybody is better off if there exists some form and extent of property rights over scarce goods (including human bodies). This realization is the ultimate pragmatic underpinning of the Decalogue's "Thou shalt not murder" and of "Thou shalt not steal"; it is the essence of the very concept of "justice" and has been the foundation of even the most basic levels of civilization.
As David Hume wrote,
the obligation to justice is founded entirely on the interests of society, which require mutual abstinence from property.
And as Mises wrote,
If history could teach us anything, it would be that private property is inextricably linked with civilization.
It did not require high philosophy to realize that the modus operandi of "snatch as snatch can" would make everyone worse off. And any group of people who did not achieve that realization would have rapidly slaughtered and starved themselves into oblivion. But exactly how property rights are delineated has varied from civilization to civilization throughout human history.
In primitive tribes, thoroughgoing egalitarianism prevented any kind of capital accumulation. In most of antiquity, to hold other human beings as chattel was considered legitimate. In caste societies property was largely a function of inherited status.
But as western Europe, beginning in the medieval era, gradually progressed away from human bondage and caste privilege, it managed to grope its way toward a property order that allowed for the advent of capitalism.
This first florescence of capitalism paved the way for its own analysis. It did so in two ways. First the wealth, leisure, optimism, tolerance, and social dynamism it generated made possible the Age of Enlightenment. Second, it provided in itself a fascinating subject of study for the Enlightenment thinkers who became the first economists — thinkers like Richard Cantillon, David Hume, the Physiocrats, and Adam Smith.
From that point forward, sound social theory, led by economics, gradually unveiled which facets of the existing moral and legal order were responsible for the new prosperity, and which facets were holding it back.
The culmination of this unveiling process is the moral/legal code promoted by Austro-liberalism. The economic works of Mises, Rothbard, and modern Austrian economists make evident that the most expedient moral and legal order, in which most any given individual is likely to benefit to the greatest degree, is the one based on the perpetual and even distant ownership of rivalrous goods that one has homesteaded or contracted for, and all rivalrous products of those goods.
Furthermore, it has arisen that security, defense, and juridical services present no exception to this rule. The Austro-anarchist tradition has made good progress in fulfilling the prediction of the first anarcho-capitalist Gustave de Molinari, that
a careful examination of the facts will decide the problem of government more and more in favor of liberty, just as it does all other economic problems.
It would make even better progress if it would not so frequently bog itself down in spinning out ingenious but spurious moral doctrines that are divorced from social utility.
Some libertarians may recoil at the thought of the pugnacious, and often emotionally satisfying, "moral argument" being resolved into its fundamental basis in social utility. They may think it deprives libertarianism of its bite, urgency, and consistency. For those libertarians, I offer another insight from Hume:
public utility is the sole origin of justice … reflections on the beneficial consequences of this virtue are the sole foundation of its merit.…
These reflections are far from weakening the obligations of justice, or diminishing anything from the most sacred attention to property. On the contrary, such sentiments must acquire new force from the present reasoning. For what stronger foundation can be desired or conceived for any duty, than to observe, that human society, or even human nature, could not subsist without the establishment of it; and will still arrive at greater degrees of happiness and perfection, the more inviolable the regard is, which is paid to that duty?
"Arguments from morality" are ultimately sterile, because they miss the point. The business end of social philosophy is to discover, and then argue for, the most socially expedient morality.
That can only be done by demonstrating how well the moral code fulfills the purpose for which moral codes are adopted in the first place: the achievement of human ends through the facilitation of the universal means of social cooperation.
And that, in turn, can only be done with the science of praxeology and its subdiscipline of economics, which reveal the systemic consequences that can be expected from general adherence to any given moral code.
 Clifford Orwin, The Just and the Advantageous in Thucydides (JSTOR).
 Ludwig von Mises, Human Action, Ch. 27, Sec. 3.
 Mises, Theory and History, Ch. 3.
 Philip Wicksteed, The Common Sense of Political Economy, Ch. 4.
 Mises, Human Action, Ch. 27, Sec. 3.
 Mises, Theory and History, Ch. 3.
 David Hume, Of Passive Obedience.
 Mises, Human Action, Ch. 15, Sec. 3.
 Murray N. Rothbard, Freedom, Inequality, Primitivism, and the Division of Labor.
 Gustave de Molinari, The Production of Security.
 David Hume, Of Justice, An Enquiry Concerning the Principles of Morals.
Originally published at Mises.org.