I want to reverse-engineer definitions of argument and self-ownership in a way that makes Hoppe’s argumentation ethics make sense. Here is my summary of Hoppe’s argument, from my previous article, with a small addition:

  1. Argument presupposes self-ownership.
  2. Argument is universal, so self-ownership is universal.
  3. Denial is a form of argument, so self-ownership can’t be denied without arguing.
  4. Any argument that denies self-ownership denies argument, and so contradicts itself.

Hoppe’s argument fails if his critics can find some way to deny self-ownership other than argument. So we must define the category of argument broadly. But it also must exclude nonsense. Here goes:
Argument is any credible means of justifying a proposition or an action.
Can I defend this definition? Perhaps Hoppe would prefer “objective” to “credible”. “Credible” is hard to pin down, but I think it expresses the thought more clearly, in spite of being harder to define.
What does it mean to justify a proposition or an action? A truth claim is justified if it is connected by correct logic and reasons to existing known truths. I will wave my hands at how we know existing known truths or what they are. Presumably that is a separate controversy.
What does it mean to justify an action? An action is justified if it is connected by correct logic and reasons to existing categories of action not prohibited by a true norm, particularly self-ownership. (For now, let’s ignore what “true norm” means in general, and just assume that Hoppe’s argument attempts to show that self-ownership is a true norm.)
In the context of argument, nonviolent action is always justified, at least, it fails to violate self-ownership. Arguing in favor of a nonviolent action (properly defined) should never cause a performative contradiction (at least, not by contradicting self-ownership). Arguing in favor of aggressive violence should always cause a performative contradiction by denying self-ownership.
(But what about arguing in favor of defensive violence? Can argument proceed without participants having a right to self-defense? If participants stick to arguing, they will have no opportunity to use self-defense, and so no need for it. Let’s set this aside for now.)
How can we define self-ownership after painting our way into this corner? Argument cannot proceed credibly if the participants are fighting, threatening each other, torturing each other, etc. Argument requires them to refrain from violence because violence lacks credibility as a means of justifying propositions and actions. If violence breaks out, argument ends. If I hold a gun to your head and force you to say you believe me, I will fail to compel your actual belief, whatever you may say while under coercion. Violence lacks credibility.
Self-ownership is a norm that prohibits aggressive violence against self-owners.