From Roderick Long's blog entry:

Hoppe offers a number of different formulations of his argument; here is a condensed reconstruction of the argument as I understand it:

1. No position is rationally defensible unless it can be justified by argument.
2. No position can be justified by argument if it denies one or more of the preconditions of interpersonal argumentative exchange.
3. Interpersonal argumentative exchange requires that each participant in the exchange enjoy exclusive control over her own body.
4. To deny the right of self-ownership is to deny exclusive control over one’s own body.
5. Therefore, the denial of the right of self-ownership is rationally indefensible.
As noted, this is my wording of the argument, not Hoppe’s. If I have misunderstood Hoppe’s argument, which is quite possible, then my criticisms will be applicable only to my reconstruction of his position, and not to his position itself. But here at any rate is a first try.

The argument appears to be logically valid; that is, the conclusion follows from the premises. Premises (3) and (4) entail that to deny the right of self-ownership is to deny one of the requirements of interpersonal argumentative exchange; premises (1) and (2) entail that no such denial is rationally defensible. Hence, (5). My worries concern the truth of the premises themselves.

Is premise (1) true? Not obviously so. It depends, I suppose, on what counts as an argument. (Does Aristotelean “negative demonstration” count? Does coherence among propositions count?) But if argument involves deriving a conclusion from premises, then (1) seems to say that no position is rationally defensible unless it can be derived from premises. But presumably the premises themselves must be rationally defensible too; deriving a conclusion from premises that are not rationally defensible is hardly going to confer rational defensibility on the conclusion. So those premises, too, must be justified by argument – and so on for the premises of that argument. Thus we are launched on an infinite regress, with the apparent upshot that no position can be rationally justified – a performatively contradictory assertion if there ever was one.

Is premise (2) true? It seems not. Consider the statement “I am the only person left alive.” One can certainly imagine circumstances in which one would be warranted in endorsing this statement on the basis of the available evidence. (The last astronaut left on the space station watches the Earth explode ....) Hence the statement could in principle be justified by argument. Yet it certainly denies one of the preconditions of interpersonal argumentative exchange – namely, the existence of other arguers.

Is premise (3) true? I don’t see why. Do you really have to have exclusive control over your entire body in order to engage in argument with me? Couldn’t I, say, have your body shackled yet leave your mouth free?

Is premise (4) true? I find it ambiguous. What does it mean for me to deny your exclusive control over your body? I might be denying the fact of your control – or the legitimacy of your control – or your right to exercise such control. These are three different things. For example, suppose you aggress against me; then I can acknowledge the fact that you are exercising control over my body, without acknowledging the legitimacy of your doing so. In the same way, then, I can acknowledge the fact that you are exercising control over your own body without committing myself to the legitimacy of your doing so. Indeed, just as I can engage in activities (e.g., self-defense) that presuppose the fact, though not the legitimacy, of your aggression against me, so I can engage in activities (e.g., argumentative exchange) that presuppose the fact, but not the legitimacy, of your control over your own body. Thus acknowledging the fact need not involve acknowledging the legitimacy.

Likewise, acknowledging the legitimacy need not involve acknowledging the right. To say that your action is legitimate is to say that you violate no moral duty in performing the action; but it doesn’t imply – as a right would – that I am morally bound not to interfere with your performance of the action. Suppose a tiger attacks me. I don’t think the tiger is doing anything immoral, since I don’t regard tigers as responsible agents. Hence I grant that the tiger’s attack is legitimate, but I still regard myself as justified in using force to defend myself. Or suppose you and I are shooting hoops, and you try to block my shot. I acknowledge the legitimacy of what you are doing, but I don’t have to let you succeed. In the same way, even if I acknowledge the legitimacy of your exercising control over your own body, that is in principle compatible with my being justified in doing my best to interfere with that control.

Premise (4) is true if denying exclusive control over one’s own body means denying the right to such control – but not if it means merely denying either the fact or the legitimacy of such control. Hence we had better interpret premise (4) as talking about the right, not the legitimacy or the fact – since that is the only interpretation that makes (4) come out true. But then, if the argument is to remain valid, premise (3) must likewise be reinterpreted to mean “Interpersonal argumentative exchange requires that each participant in the exchange enjoy a right to exclusive control over her own body.” But why should we grant the truth of (3), under that interpretation? Whatever plausibility (3) had came from interpreting it as talking either about the fact or the legitimacy, not the right. When (3) is interpreted as talking about the right, it starts looking less like a premise and more like the intended conclusion.

I have two broader, Austro-Athenian worries about Hoppe’s argument. (They may actually just be two different ways of stating the same worry.) First: to defend the existence of libertarian rights is to defend a view about the content of justice – but as an Aristotelean, I’m inclined to doubt that the content of justice can be settled apart from the content of the other virtues, or of the good life generally. Second: Hoppe’s argument, if it worked, would commit us to recognising and respecting libertarian rights regardless of what our goals are – but as a praxeologist, I have trouble seeing how any practical requirement can be justified apart from a means-end structure.

As I said at the beginning, I think a Hoppe-style argument might well work; but before I could be convinced I’d want to see such an argument a) distinguish clearly whether it is the fact, the legitimacy, or the right of self-ownership whose denial is being refuted, and b) embed its normative force in a Classical Eudaimonist framework.