Hoppe's Argumentation Ethics: The Internal Proof for Natural Law

Ludwig von Mises made a monumental contribution to Philosophy by grounding Kantian categories of the mind into categories of action. Kant had challenged philosophy and science with the possibility of synthetic a priori knowledge—truths about reality knowable independent of experience. Mises accepted that challenge and relocated it: the categories aren't pre-existing structures of consciousness, but presuppositions embedded in human action itself.

This breakthrough opened two revolutionary paths. First, it established Mises's praxeological approach in Economics, demonstrating essential theorems and laws from the axiom of purposeful action without recourse to empirical testing. But second—and equally profound—it laid groundwork for future students like Hans-Hermann Hoppe, who would extend those same axioms and premises into Ethics (and Law) itself.

Hoppe's Argumentation Ethics stands as one of the most ingenious defenses of libertarian property rights ever developed. But its true significance lies not in opposition to natural law theory—it's a subset that fortifies Thomistic natural law from within.

When Murray Rothbard first was presented Hoppe's argumentation ethics in the late 1980s, he celebrated it as a breakthrough. Here was a defense of private property that didn't rely on theological premises or contested empirical claims about human flourishing. Instead, it demonstrated that anyone who argues—about anything—must presuppose the very property norms libertarians defend. To deny libertarian ethics while arguing is performatively contradictory.

But Rothbard understood something deeper. Rothbard was influenced by Thomas Aquinas's philosophy (Thomism). The Thomists believe that all beings (including humans) have a nature and their nature has telos (end) that can be known by human reason. For the Thomists, a universal ethic needs to be compatible and derive from this human nature. Hoppe's contribution wasn't an alternative to this tradition—it was its most rigorous internal validation.

The Thomistic Foundation: Human Nature as Knowable

Natural law theory rests on a straightforward claim: humans have a specific nature, knowable through reason, and ethical norms derive from that nature. As Rothbard emphasized in The Ethics of Liberty, this doesn't require theological premises. The Jesuit Suarez pointed out that many Scholastics had taken the position that the natural law of ethics, the law of what is good and bad for man, does not depend upon God's will. Indeed, some of the Scholastics had gone so far as to say that even though God did not exist, or did not make use of His reason, or did not judge rightly of things, if there is in man such a dictate of right reason to guide him, it would have had the same nature of law as it now has.

The challenge for natural law theorists has always been specifying what counts as "human nature." The concept is admittedly broad. Humans eat, sleep, reason, procreate, create art, form societies. Which features are ethically relevant? And how do we derive specific norms—like prohibitions against theft or assault—from general observations about human biology and psychology?

This is where Hoppe's contribution becomes decisive. It is not the wider concept of human nature but the narrower one of propositional exchanges and argumentation which must serve as the starting point in deriving an ethic. Moreover, there exists an a priori justification for this choice insofar as the problem of true and false, of right and wrong, does not arise independent of propositional exchanges.

Argumentation as the Essence of Human Nature

Hoppe's insight was to recognize that human nature, in its ethically relevant dimension, is the nature of a being capable of argumentation. This isn't arbitrary. Ethics only matters for beings who can dispute what ought to be done. Rocks and trees don't need ethics. Even non-human animals, lacking propositional language, don't engage in ethical debates about property rights.

Humans are different. We are the species that argues about how to live, what rules should govern us, who owns what. This capacity for argumentation isn't incidental to our nature—it's the defining feature that makes ethics necessary and possible.

Argumentation is a type of human action and therefore is ruled by praxeology laws. Hoppe used the same definition of argumentation as Apel and Habermas, but this insight enabled him to know that argumentation presupposes the utilization of the person's body as the primary means of action. When you argue, you must use your body—your vocal cords, your brain, your hands to gesture or type. And you must use external resources—air to carry sound, space to stand in, time to formulate thoughts.

Argumentation, therefore, presupposes property rights. Not as something we should respect, but as something we must presuppose to argue at all. To argue against property rights, you must first claim property in your body (to speak) and in scarce resources (to exclude others from using your vocal cords simultaneously or occupying the same space).

The Synthetic A Priori: Hoppe's Post-Kantian Method

Hoppe employs what he calls a synthetic a priori approach, following Kant's distinction between analytic truths (true by definition) and synthetic truths (describing reality). Mises and Hoppe, being post-Kantians or even anti-Kantians (in the sense that they answered his challenge or "grounded" his system that got many philosophers "stuck" in a few ways), justify it rationalistically; that is, they consider that to deny this proposition is to affirm it. For one cannot deny that humans act purposefully without acting purposefully. Therefore, such an axiom is a result of the application of the laws of logic and is dependent on an apriori way of thinking.

This differs from Rothbard's epistemology. In slight distinction with Hoppe and Mises, Rothbard finds his epistemological roots in the empirical tradition of Thomas Aquinas. Thus, he considers the proposition that "human beings act purposefully" to be founded on experience, on observing both one's self and other humans.

But this methodological difference doesn't create opposition—it creates complementarity, in my view. Rothbard's Thomistic approach identifies human nature through observation and reason. Hoppe's argumentation ethics provides an internal proof for it: it shows that anyone who argues must presuppose the very norms that natural law theorists independently derive from observing human nature.

Bridging the Is-Ought Gap Without Crossing It

Natural law theorists have long struggled with Hume's is-ought problem: how do you derive normative claims (what ought to be) from descriptive claims (what is)? Hoppe's solution is elegant. It remains entirely in the realm of is-statements and never tries to derive an "ought" from an "is." The structure of the argument is this: (a) justification is propositional justification — a priori true is-statement; (b) argumentation presupposes property in one's body and the homesteading principle — a priori true is-statement; and (c) then, no deviation from this ethic can be argumentatively justified — a priori true is-statement.

Hoppe doesn't claim to derive oughts from is. He demonstrates that if you engage in argumentation at all, you've already presupposed certain norms. The "ought" is embedded in the practice of arguing itself. To argue against private property is to perform a contradiction—using your property (your body, your time, the space you occupy) to deny the legitimacy of property.

This is the "internal" proof for natural law. It doesn't tell us that humans should argue or that argumentation is morally superior to violence. It shows that argumentation, as an activity, presupposes the norms that natural law theorists defend on other grounds.

Scarcity and Original Appropriation

The connection deepens when we consider scarcity. Conflict exists in a world of scarce resources and therefore property assignment rules are to be demanded. In order for one to justify any of these rules, that is, in order to put forth an argument in defense of a political theory, one must presuppose self-ownership.

Human action—including argumentation—takes place in a world of scarcity. Multiple people cannot simultaneously occupy the same space or use the same vocal cords. Property rights emerge as the solution to potential conflicts over scarce resources. And the original appropriation principle—homesteading—follows necessarily: the first person to use a previously unowned resource establishes a better claim than later arrivals who wish to dispossess him.

This is exactly what Thomistic natural law theorists argue from a different starting point. Humans have a nature that requires using scarce resources. Conflicts arise over these resources. Reason dictates rules that minimize conflict and enable human flourishing. Those rules happen to be the libertarian property norms.

Hoppe's argumentation ethics confirms this from within the practice of ethical discourse itself.

Fortification From Within

Natural law theory faces external challenges: skeptics who deny that human nature exists, relativists who claim ethics are culturally constructed, utilitarians who subordinate rights to consequences. Hoppe's argumentation ethics doesn't answer all these challenges—but it makes one crucial contribution.

It shows that anyone who argues about ethics—including the skeptic, the relativist, the utilitarian—has already presupposed the libertarian property norms. You can refuse to argue. You can simply use violence without justification. But the moment you try to justify your use of violence, or argue that property rights don't exist, you've implicitly recognized property rights by claiming your body as exclusively yours for the duration of the argument.

This is fortification from within. Even if someone rejects the broader Aristotelian-Thomistic framework—rejects teleology, rejects that human nature determines ethical norms—they cannot reject the norms presupposed by argumentation without contradiction. As long as humans are the species that argues about what ought to be done, argumentation ethics provides an internal proof for the norms natural law theory defends.

Reconciling the Traditions

The reconciliation works because both traditions identify the same reality from different angles. Thomistic natural law observes human nature—including our capacity for reason and argument—and derives ethical norms. Hoppe's argumentation ethics examines the presuppositions of argumentation itself and discovers those same norms embedded in the practice.

As one scholar notes, Hoppe's approach solves a persistent problem in natural law theory: It has been a common quarrel with the natural rights position, even on the part of otherwise sympathetic observers, that the concept of human nature is far too diffuse to allow the derivation of a determinate set of rules of conduct. The praxeological approach solves this problem by recognizing that it is not the wider concept of human nature but the narrower one of propositional exchanges and argumentation which must serve as the starting point.

Human nature, in its ethically decisive feature, is the nature of beings capable of argumentation. Natural law theorists arrive at this through observation and philosophical reflection. Hoppe demonstrates it through transcendental analysis of argumentation's presuppositions. Both paths lead to the same destination: libertarian property rights are grounded in human nature itself.

Rothbard celebrated Hoppe's contribution because he saw it for what it was—not a replacement for natural law theory, but its most rigorous internal validation. The fortress of natural law now has walls reinforced from both without (the Aristotelian-Thomistic tradition) and within (argumentation ethics). Anyone who wishes to storm that fortress must first explain how they can argue against it without presupposing its truth.

Aspect	Hoppe's Argumentation Ethics	Thomistic Natural Law	Reconciliation via Rothbard
Method	Post-Kantian synthetic a priori; performative contradictions in discourse.	Aristotelian demonstrative reason from human nature/teleology.	Praxeological axioms as NL foundation; AE as breakthrough generalizing ethics without values.
Human Nature	Species capable of argumentation; presupposes self-ownership for action.	Rational being oriented to goods like knowledge; reason discovers moral principles.	AE demonstrates NL's rational essence; property from will's proprietorship.
Scarcity & Property	Action in scarcity generates homesteading to resolve conflicts.	Secondary precepts preserve life; appropriation aligns with flourishing.	Homesteading as labor mixing; AE fortifies via contradiction in denial.
Proof Type	Internal: Presuppositions of argumentation prove norms.	External: Derived from eternal law/human inclinations.	AE as internal fortification; complements NL's radical critique of statism.

Addressing Common Criticisms of Argumentation Ethics

While Hoppe's argumentation ethics (AE) provides a robust internal proof for natural law norms, it has faced several critiques that merit attention. One prominent criticism, advanced by Robert P. Murphy and Gene Callahan, argues that AE establishes only limited or temporary self-ownership: participants in debate presuppose control over body parts essential for argumentation (e.g., mouth, brain) solely during the discourse, not permanent or full ownership of the entire body or external resources. This view posits that a collectivist could argue against absolute rights without contradiction, as long as force (e.g., for redistribution) occurs outside the debate. Similarly, Jonathan Ashbach contends that AE's methodology is faulty, as argumentation does not inherently assume ethical precepts; a nihilist might argue strategically without moral implications, and teleological ethics could justify limited rights for higher ends like the common good. Another refutation highlights a conflation of liberty rights (permission to argue) with claim rights (duties on others), suggesting AE proves only the former, not libertarian self-ownership.

These critiques, however, do not undermine AE's compatibility with Thomistic natural law; rather, they highlight its scope as a complementary demonstration. Defenders like Frank van Dun respond that AE is a priori and dialectical, extending beyond the immediate argument: denying self-ownership post-debate without justification excludes one from rational discourse, as argumentation presupposes treating others as free, equal persons universally. Even if AE yields only contextual rights, this aligns with natural law's secondary precepts, which derive situational norms from human nature's rational essence. Rothbard himself viewed AE as transcending such limits by generalizing ethics value-free, fortifying natural law against empiricist challenges. Thus, while AE may not prove absolute libertarianism in isolation, it strengthens Thomism by evidencing argumentative human nature, with critiques inviting refinement rather than rejection.

Criticism	Key Proponents	Core Argument	Defense in Context of Natural Law
Limited Self-Ownership	Murphy/Callahan, Ashbach	Only temporary/partial rights during debate	Dialectical extension makes rights enduring; aligns with NL's secondary precepts
No Performative Contradiction	Ashbach	No ethical assumptions in arguing	A priori presuppositions treat arguers as free persons, evidencing rational human nature
Conflation of Use and Rights	Murphy/Callahan, Bleeding Heart	Use ≠ ownership; liberty ≠ claim rights	Synthetic a priori embeds norms; complements Thomistic teleology for flourishing

In sum

In conclusion, Hoppe's argumentation ethics serves as a vital subset of Thomistic natural law, providing an internal proof that human nature—as that of a species capable of argumentation—necessitates ethical norms like self-ownership and property rights in a world of scarcity. This reconciliation, as Rothbard insightfully recognized, bridges post-Kantian methods with Aristotelian-Thomism, fortifying the tradition against external challenges while enriching its philosophical arsenal. Ultimately, it underscores that libertarian ethics are not arbitrary but inescapably grounded in the logic of rational discourse, offering a timeless framework for resolving conflicts and promoting human flourishing.

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Juan Fernando Carpio, M.E.E.

Sources:

• Hoppe, Hans-Hermann. "A Primer on Hoppe's Argumentation Ethics." Mises Institute, 2024.
• Maciel, Lucas. "An Interpretative Model of the Evolution of Hoppe's Argumentation Ethics." Studia Humana 9.2 (2020).
• Rothbard, Murray N. The Ethics of Liberty. New York University Press, 1998.
• Meng, Jude Chua Soo. "Hopp(e)ing Onto New Ground: A Rothbardian Proposal for Thomistic Natural Law." 2002.