Followers of Rothbard invoke the non-aggression principle (NAP) as the standard against which the permissibility of any action is to be judged. But the NAP is insufficient for this use.  I call this idea non-aggression principle insufficiency. NAPI for short.

The problem is not that the NAP gets the important basics right and supplemental detail can be derived in other ways. NAPI means recognising that the NAP is completely dependent on integration with subjective, contingent legal opinion. Without this arbitrary line drawing, the NAP has nothing to say about the permissibility of any action in the world. For instance, the NAP alone is insufficient to conclude that taxation is theft.

What the NAP means

Here Murray Rothbard explains the NAP (emphasis added).

No one may threaten or commit violence ('aggress') against another man's person or property. Violence may be employed only against the man who commits such violence; that is, only defensively against the aggressive violence of another. In short, no violence may be employed against a nonaggressor. Here is the fundamental rule from which can be deduced the entire corpus of libertarian theory.

So the NAP forbids aggression, which resolves to 'violence against another man’s person or property', which in turn resolves to 'anything that violates property rights'.

The indeterminate NAP

Natural-law libertarians like Rothbard uphold a neo-Lockean view of property rights. But in order to derive a judgement about permissibility of any real-world action from this theory, a set of questions about line drawing need to be answered. And it isn’t clear how the answers to this set can be derived from theory. For instance:

  • Exactly how visible must a property boundary be? How should its visibility be tested?
  • How long must a property be vacant, and under what circumstances, in order to be considered abandoned?
  • How much 'labour’, and of what kind, must be 'mixed with the land' in order for it to be considered homesteaded?

David Friedman has some excellent illustrations of NAPI towards the end of his book The Machinery of Freedom, in the chapter with the opaque title ‘Problems’.

If I fire a thousand megawatt laser beam at your front door I am surely violating your property rights, just as much as if I used a machine gun. But what if I reduce the intensity of the beam—say to the brightness of a flashlight?

We likely agree that it’d be unreasonable and undesirable to prohibit photon trespass in the case of very low light levels. That means that there must be some threshold of intensity below which emitting light that reaches your neighbour should be permissible. What is that threshold? Neither natural law, nor the NAP tell us.

Carbon dioxide is a pollutant. It is also an end product of human metabolism. If I have no right to impose a single molecule of pollution on anyone else's property, then I must get the permission of all my neighbors to breathe.

Again, nobody is an advocate of a regime in which a person must get permission to breath. So implicitly we have an idea of an acceptable level of pollution and an unacceptable level. The NAP doesn’t help us find the proper place to draw that line.

A similar problem arises if we consider effects that are small not in size but in probability. Suppose I decide to play Russian roulette, with one small innovation; after putting one cartridge in my revolver and spinning the cylinder, I point it at your head instead of at mine before pulling the trigger. [...]
what if the revolver has not six chambers but a thousand or a million?
I take off from an airport in a private plane with a cruising radius of a thousand miles. […] There is some probability that the plane, […] will crash. There are things I can do which will reduce these probabilities, but not to zero. It follows that by taking off I impose some (small) probability of death and destruction on everyone through whose roof I might crash.

We would like to forbid the involuntary game of Russian roulette, but perhaps not the plane flight. So we’d like to draw the line of permissibility somewhere between the two. Notice again that the NAP has nothing to say about the the extent to which we should allow exposing other people to the risk of harm without their consent.

From the NAP to taxation is theft?

Does the NAP forbid taxation at least?

On its own, no. If the state was the rightful owner of the land on which its subjects live, it's plausible that taxation is legitimate (meaning permitted, by the lights of libertarian natural-law). The NAP offers no way of testing the claim that the state is the rightful owner of the land.

  • This is because it doesn’t specify homesteading criteria in any testable way
  • it doesn’t specify the conditions under which property should be considered abandoned by its previous owner
  • It doesn’t specify how restitution should be handled (if at all) in the case of rights violations.
  • It doesn’t say anything about how historic misdeeds committed by long-dead agents of a trans-generational institution must be remedied.

All of these questions will involve arbitrary line drawing, and subjective opinion.

The significance of NAPI for libertarian rhetoric

The incompleteness of the NAP is significant for libertarian rhetoric. Most claims relating to whether a behaviour violates the NAP are underdetermined.

That's because the NAP provides no guidance on the permissibility of any given behaviour, until it's allied with  subjective and contingent rulings about where to draw lines on gradients. By that I mean rulings on questions of this sort: "what degree of caused physical change constitutes legally significant 'transformation' or 'trespass'".

So contrary to what Rothbard believed, deriving rules about permissible action isn’t a project that can be carried out through the unadulterated application of “reason and rational inquiry”.

The libertarian NAP invoker unwittingly shirks the messy duty of defending the locations of all the implicit lines that his conclusion, like ‘taxation is theft’, has to assume.

Further reading

Read more? All articles

I create videos with the help of my patrons great and small.
Find out more about supporting my work.

Would you like to get emails now and then when I publish new things? Leave your address here.