Murray Rothbard wrote that libertarian anarchism rests upon the principle of non-aggression, which he defined as the belief that no individual or group of individuals may aggress (that is, use violence or the threat of violence) against the person or property of anyone else. Examples of aggressing against someone’s person include enslaving him, as well as restricting his freedom to speak, publish, and assemble. Examples of aggressing against someone’s property include seizing his property and dictating the manner in which it may be used.[i]
Unfortunately for anarchists, a strong case can be made that the principle of non-aggression is not universally valid. To see why this is so, one merely needs to think of a hypothetical situation that would seem to justify violating the principle. For instance, imagine you’re sitting at a bus stop with a friend. The friend suddenly starts having a diabetic attack and you know that unless you can get him some sugar in the next few minutes he’s going to die. Looking over, you see a woman waiting for the bus, munching on a Snickers bar. You ask if you can have the Snickers to give to your friend. She says no. You plead with her. She says no. You offer to buy the candy bar from her. She still says no. You look back at your friend, who’s quickly nearing death. What do you do?
Well you forcibly take the candy bar. Obviously. Now, of course, it’s impossible to prove that you’re morally justified in taking the candy bar. But then again, as numerous philosophers have shown, it’s impossible to prove that any action is morally justified.[ii] Nonetheless, most of us would agree that we can have knowledge of certain moral principles.[iii] And I think that all of us, or at least most of us, would also agree that you’re morally justified in taking the candy bar.
From this, it follows that there is at least one conceivable situation in which one would be justified in violating the principle of non-aggression. Which of course means that the principle is not universally valid. And this in turn means that libertarian anarchism no longer has an unshakable foundation. Or to put it another way, since an individual can conceivably be justified in aggressing against another person, it’s certainly possible that a group of individuals—and thus a government—can conceivably be justified in aggressing against another group of individuals.
Before we see if there might be another way to justify anarchism, let’s focus a little longer on the principle of non-aggression. Though not universally valid, I think a case can be made that the principle is almost universally valid. For, excluding times one acts in defense, it’s difficult to think of many situations in which one is justified using aggression against someone else’s person or property. For this reason, the principle of non-aggression can be likened to many of our most deeply held moral precepts—for instance, the prohibition against lying. Though there seem to be times when it is morally imperative to lie (for example, Nazis coming to Corrie ten Boom’s front door and asking if she’s hiding any Jews), all of us would hold that, except in rare circumstances, lying is wrong.
Because the principle of non-aggression is almost universally valid, it can be a great tool for anarchists. For the principle can be used to show that almost, though perhaps not every, action undertaken by the state is immoral. As Rothbard writes, if we apply moral standards to everyone, not making exceptions for any individual or any group of individuals, including the state, then we can see that the state is allowed to commit all sort of acts that “even non-libertarians concede are reprehensible crimes. The State habitually commits mass murder, which it calls ‘war,’ or sometimes ‘suppression of subversion’; the State engages in enslavement into its military forces, which it calls ‘conscription’; and it lives and has its being in the practice of forcible theft, which it calls ‘taxation.’”[iv]
So the principle of non-aggression is a tool that can be used to debunk almost everything the state does. Or to change our metaphor, it is a filter that eliminates all, save perhaps minarchist, governments.
It’s still possible to save anarchism, however. For instance, we could argue something like the following: (1) Because human nature is what it is, all governments, even minarchist ones, inevitably become bigger and more intrusive; (2) Anarchism is morally superior to any government bigger and more intrusive than a minarchist one; therefore (3) Anarchism is morally justified. Determining whether this argument is sound, however, will have to wait for another day.
 Murray Rothbard, For a New Liberty: The Libertarian Manifesto (Murray Rothbard, 1973; reprint, Auburn: Ludwig Von Mises Institute, 2006), 27-28.
 A proposition is proven to be true when that proposition is inferred from other, pre-established propositions. Therefore, if morality could be proven to be true, all moral propositions would ultimately have to be inferred from other propositions. Needless to say, these other propositions would either have to be moral or non-moral ones. However, it is absurd to say that moral propositions can be ultimately inferred from other moral propositions. For, if we want to avoid an infinite regress of inferences, we must acknowledge that, if moral propositions were ultimately inferred from other moral propositions, then these latter propositions would themselves be unprovable. And, if this were the case, it would follow that morality is ultimately unprovable. And it is impossible to infer moral propositions from non-moral propositions. As Hume put it, it is impossible to infer an ought statement from an is statement. This is so because, in order to infer a conclusion from a set of premises, one must show that the conclusion is already contained in the premises and that merely connecting the premises brings this conclusion to light. For example, the following syllogism is valid because the conclusion is found by simply connecting the premises: (1) Jack stole from Jill; (2) Stealing is wrong; (3) Therefore, Jack’s stealing from Jill was wrong. This next conclusion, on the other hand, is not valid because the conclusion is not contained in the premises: (1) Jack stole from Jill; (2) Jack has brown hair; (3) Therefore, Jack’s stealing from Jill was wrong.
 Let me here provide a brief argument for my claim that we can have knowledge of certain moral principles. Let me begin by noting that, just as it’s impossible to prove that any action is morally justified, it’s impossible to prove that we can have knowledge of any moral principle. But this in no way implies that we can’t be epistemically justified in believing such propositions. For there are many propositions that we’re justified in believing even though we can’t prove them: for instance, the proposition, “My senses are generally reliable.” Though most all of us believe this proposition, it’s impossible to prove it. As many philosophers have pointed out, it’s logically possible that you’re just a brain floating in a vat somewhere who is hallucinating the external world.
All the same, philosophers have long contended that people are justified in having a whole host of beliefs that cannot be proven. Such beliefs are generally referred to as basic beliefs. Simply put, a basic belief is a belief that we know to be true even though we cannot prove it to be true. While some basic beliefs can be known with infallible certainty (e.g., “I exist”), others can only be known with a prima facie certainty (e.g., “My senses are generally reliable”) [W. Jay Wood, Epistemology: Becoming Intellectually Virtuous (Downers Grove, IL: InterVarsity Press, 1998), 98]. Many of our traditional moral values, it seems to me, fall in the latter category.
Proof that these values are basic beliefs is that they possess the same essential characteristics as other basic beliefs. Basic beliefs, W. Jay Wood writes, are “the sort of convictions that are universally subscribed to, indispensable for living, beliefs to which we are irresistibly drawn from our earliest moments of our lives and which are rooted in our very psychological natures” [Ibid., 101].
Let me briefly offer two pieces of evidence that at least some of our traditional moral values possess these characteristics. First, many of these values are nearly universally subscribed to. This is the conclusion C.S. Lewis reached after surveying the moral codes of the ancient Egyptians, Jews, Babylonians, Hindus, Chinese, Greeks, Romans, and Christians. As he writes, “[T]hough there are differences between the moral ideas of one time or country and those of another, the differences are not really very great—not nearly so great as most people imagine—and you can recognize the same law running through them all” [C.S. Lewis, Mere Christianity (New York: Macmillan Publishing, 1943; reprint, New York: Macmillan Publishing, 1986), 10]. For instance, “Men have differed as regards what people you ought to be unselfish to—whether it was only your own family, or your fellow countrymen, or everyone. But they have always agreed that you ought not to put yourself first. Selfishness has never been admired. Men have differed as to whether you should have one wife or four. But they have always agreed that you must not simply have any woman you liked” [Ibid., 5]. Moreover, the anthropological discoveries made over the past hundred years have shown that similar basic moral principles can be found in all cultures. As anthropologist Clyde Kluckhohn writes, “Every culture has a concept of murder, distinguishing this from execution, killing in war, and other ‘justified homicides.’ The notions of incest and other regulations upon sexual behavior, the prohibitions upon untruth under defined circumstances, of restitution and reciprocity, of mutual obligations between parents and children—these and many other moral concepts are altogether universal” [Clyde Kluckhohn, “Ethical Relativity: Sic et Non,” Journal of Philosophy, LII (1955); quoted in Louis Pojman, Moral Philosophy (Indianapolis: Hackett Publishing, 1998), 45].
Second, many of our traditional values are principles that humans, beginning at an early age, just can’t seem to disbelieve. One evidence Lewis gives for this is that even those who claim that morality is subjective are unable to actually hold to their subjectivism. As he writes, “He [the subjectivist] may break his promise to you, but if you try breaking one to him he will be complaining ‘It’s not fair’ before you can say Jack Robinson” [Lewis, Mere Christianity, 5]. Similarly, those who attempt to reject traditional morality and create their own values reveal that they believe in traditional morality by the fact that the new values they create are derived from traditional morality. A prime example of this is Friedrich Nietzsche, who perhaps came as close as any other philosopher to actually rejecting traditional morality. Although he would have certainly denied it, Nietzsche fervently held to many traditional moral values. For instance, he condemned “Christian morality” by appealing to a number of traditional moral values which he believed Christian morality violated—e.g., he condemned the Christian values of charity, equality, and justice because he believed Christians only preached and practiced these values because they were filled with hatred and resentment towards the “strong,” and because they hoped they could execute revenge on the strong by preaching and practicing these values. Likewise, he seemed to criticize the Christian value of humility because he believed that those who attempted to practice it were generally disingenuous.