Historicism asserts that the logical structure of human thought and action is liable to change in the course of historical evolution.
[Ludwig Von Mises, Human Action, page 5.]

Below we will show that propositions concerning property justice must be compatible with argumentation. They can satisfy this condition in one of two ways, either by describing universal truths that apply to all persons at all times, or by describing arbitrary truths that depend upon the act of argumentation. So persons who wish to formulate a proposition that describes a principle of justice have three alternatives:

  1. Embrace incompatibility with argumentation and therefore self-contradiction, or
  2. Embrace an extremely arbitrary form of historicism that treats persons differently depending upon whether they are participating in argumentation at a particular moment or not, or
  3. Use universal statements that are compatible with argumentation.

Here is the proof:

  1. Assume ∀p ∀t A(p,t) => q(p,t). [Argumentation presupposes q. If person p is arguing at time t, q is true.]
  2. Assume ∃p0 ∃t0 A(p0 ,t0) & ~q(p0 ,t0) [Person p0 disputes q(p0 ,t0) at time t0.] 
  3. q(p0 ,t0) [Follows from 1 and 2. But this is a contradiction, so our assumptions 1 and 2 are incompatible.]
  4. ∃p ∃t q(p,t). [Follows from 3.]
  5. ~(∀p ∀t ~q(p,t)). [Follows from 4. We have a counterexample (p0 ,t0), so the universal negation of q is false.]
  6. (∀p ∀t q(p,t)) or (∃p ∃t ~q(p,t)) [We proved q is not universally false, so either q is universally true, or there is an exception to q. q is universalizable or historicism. We have made no assumption about p0 or t0 except p0 is arguing at t0. But this assumption prevents us from immediately generalizing to all persons. We can generalize only to all arguers while they argue. But we have disproved the universal form of ~q, so either q is universal or some version of historicism is true.].
  7. assume ∃p ∃t ~q(p,t). [Assume historicism is true.]
  8. ~q(p1,t1). [Let p1, t1 be the counterexample.]
  9. ~q(p1,t1) => ~A(p1,t1). [Follows from 1.]
  10. ~A(p1,t1). [Follows from 9 and 10. The person p1 in the counterexample is not arguing at time t1.]

We have proved that if argumentation presupposes q, then either q is universally true for all persons at all times, or a very peculiar version of historicism holds. It is an arbitrary historicism, which depends only on whether or not a person is arguing at a particular moment.
It is not the historicism of Marx, who thought that principles of justice changed with material conditions. Marx never based his ideas about property on the owner’s ability to argue, or even less on whether the owner was in the act of arguing or not. This historicism is much more arbitrary. While it is compatible with argumentation (by assumption), it is incompatible with common sense.
Hardy readers of my blog will recognize that this as another variant of the logic of Hoppe’s argumentation ethics. (I apologize for not getting it quite finished on the first few tries.) But note that the logic has abstracted from any specific issue raised in Hoppe’s argument, other than pure logic of what sort of generalizations are compatible with argumentation. Now that we have developed the logic, we must apply it, and that is the true test of Hoppe’s idea. By presenting it in this way, I hope to separate questions of interpretation from questions of pure logic.
In this light, we can see how the criticisms of Hoppe provided by Murphy and Callahan missed the mark. They correctly intuited the existence of the “arbitrary historicism” option, but interpreted this as a gap in Hoppe’s argument. In my interpretation of Hoppe, I reject the “arbitrary historicism” option by pointing out that no serious proposal for a property rights regime or ethical system would embrace such arbitrariness. Only universal propositions are serious candidates, and they must be compatible with argumentation. Propositions that are incompatible with argumentation are false, and this is Hoppe’s important conclusion.
This approach to the logic also saves Hoppe from the logical criticisms provided by Frederick. Frederick sought to make Hoppe’s pragmatic contradiction idea more explicit, but provided a flawed version of the logic. I have provided a more successful and charitable interpretation of the logical argument.
That said, we see that the serious critic of Hoppe’s approach still has many ways of attacking the idea, most particularly by questioning whether indeed argumentation presupposes anything that discriminates between varieties of property proposals. The logic may be perfectly correct, but if no predicate can substitute for q and make the assumptions of the logic hold with respect to property arrangements, then the logic does not apply to such arrangements, and Hoppe fails.
I keep writing as if I intend to complete this analysis, this “argumentation ethics for dummies”, and indeed I hope to. I keep putting it off, hoping that I can clarify my understanding enough to treat the subject fairly. Perhaps I am nearly there.