Matt Zwolinski says we should scrap the non-aggression principle: It gives easy answers in some places, but it stumbles in others. Better to just replace it, he argues:

[T]he NAP’s plausibility is superficial. It is, of course, common sense to think that aggression is a bad thing. But it is far from common sense to think that its badness is absolute, such that the wrongness of aggression always trumps any other possible consideration of justice or political morality. There is a vast difference between a strong but defeasible presumption against the justice of aggression, and an absolute, universal prohibition. As Bryan Caplan has said, if you can’t think of counterexamples to the latter, you’re not trying hard enough.

My sense is that both Zwolinski and Murray Rothbard, the NAP’s key exponent, may be asking too much of their models. Rothbard for his part doesn’t seem to notice when the model isn’t delivering. That’s why he gives what are in my view some unconscionable recommendations about children. Zwolinski is right to reject them:

It’s one thing to say that aggression against others is wrong. It’s quite another to say that it’s the only thing that’s wrong – or the only wrong that is properly subject to prevention or rectification by force. But taken to its consistent extreme, as Murray Rothbard took it, the NAP implies that there is nothing wrong with allowing your three year-old son to starve to death, so long as you do not forcibly prevent him from obtaining food on his own. Or, at least, it implies that it would be wrong for others to, say, trespass on your property in order to give the child you’re deliberately starving a piece of bread. This, I think, is a fairly devastating reductio of the view that positive duties may never be coercively enforced. That it was Rothbard himself who presented the reductio, without, apparently, realizing the absurdity into which he had walked, rather boggles the mind.

Partly as a result, Zwolinski seems to think we need to give up on the NAP as well. First he recommends a “defeasible presumption”—probably the right approach, I’d say—but in his conclusion, he seems to aim at something much larger. Though not necessarily better:

Libertarians are ingenious folk. And I have no doubt that, given sufficient time, they can think up a host of ways to tweak, tinker, and contextualize the NAP in a way that makes some progress in dealing with the problems I have raised in this essay. But there comes a point where adding another layer of epicycles to one’s theory seems no longer to be the best way to proceed. There comes a point where what you need is not another refinement to the definition of “aggression” but a radical paradigm shift in which we put aside the idea that non-aggression is the sole, immovable center of the moral universe. Libertarianism needs its own Copernican Revolution.

We are ingenious folk! But it’s not clear we need anything as clever, or large, as a Copernican Revolution.

Since we’re on the subject, let’s talk physics. To model how a billiard ball rolls on a table, one makes simplifying assumptions—the table is a perfectly flat plane, the ball is a perfect sphere, the mass is distributed equally, and the like. One does these things not because the simplified model is perfectly true to life, but for three related reasons: (1) the model is often close enough; (2) the math is vastly easier; and (3) you can use it to say things that are more or less true about billiard balls anywhere: here, in Spokane, and—with only minor adjustments—on Mars.

Moral and political philosophy should be like that. They should make simplifying assumptions. They must, if they are to do anything more than reference isolated cases without any extensive explanatory power. And the ability to extend to additional cases is the very reason we do philosophy, at least as a practical matter.

This is why Michael Huemer’s treatment of the non-aggression axiom seems like a significant step forward to me. To Huemer, the non-aggression principle is not really an axiom at all; it’s a strong but rebuttable presumption. That may seem like a weakening to a lot of folks, but if so they should consider the radicalism of Huemer’s conclusions as evidence that he’s not going weak in the knees.

By contrast, I have to say Zwolinski’s objections sound as if he is indicting libertarianism for saying that the billiard ball was a sphere, while only he knows, sadly, that spheres have nothing to teach us about billiards. Granted, the first was false, but so is the second.

Spheres are a good solid start to the problem, and we ought not to feel too badly about needing refinements from time to time. The word for these refinements is not epicycles, however. It’s engineering.

I think this analogy points the way toward solving many of the conundrums Matt poses in his post. Many of his difficulties, including children, pollution, and the need for a clear definition of property, are all a part of building models that meet particular real-world circumstances. Of course abstract theory has much to tell us. And of course it can’t tell us everything.

In one case, though, I will commend to him a useful solution that doesn’t fit the above. His fourth conundrum holds that fraud is unrelated to force, and that a libertarian society might find itself embarrassingly unable to punish fraud. I disagree.

Fraud is wrong because it, like physical force, defeats the will without convincing the intellect. As such:

[Force and fraud] are both impediments to reflective self-rule, and any political theory that values reflective self-rule is permitted to find them similar problems. This is why both are properly censured in libertarian political thought… While there remain many salient differences between force and fraud, the likeness is not imaginary or arbitrary, at least not any more so than are concepts like “will” and “intellect.”

It’s okay to use force to combat fraud, just as it’s okay to use force to combat a physical aggressor. It may not even be too much to say that both force and fraud are species of some larger genus, albeit one that lacks a name in our language. Both acts attempt to subvert individual atuonomy, and both may therefore be treated alike, at least if we do value individual autonomy as our highest political end.

I’d add that we libertarians are a good deal more consistent than most about the censure here—we wouldn’t make exceptions and allow the initiation of force simply because some people call themselves “the state.” But the intuitions that force and fraud are almost always wrong, and that they are wrong in similar ways, are both very common. They are not at all weird, and, used properly, they constitute a strong argument for our side. They ought not to be rejected.