ON PRAXEOLOGY AND THE PRAXEOLOGICAL FOUNDATION OF EPISTEMOLOGY I

As have most great and innovative economists, Ludwig von Mises intensively and repeatedly analyzed the problem of the logical status of economic propositions, i.e., how we come to know them and how we validate them. Indeed, Mises ranks foremost among those who hold that such a concern is indispensable in order to achieve systematic progress in economics. For any misconception regarding the answer to such fundamental questions of one’s intellectual enterprise would naturally have to lead to intellectual disaster, i.e., to false economic doctrines. Accordingly three of Mises’s books are devoted entirely to clarifying the logical foundations of economics: His early Epistemological Problems of Economics, published in German in 1933; his Theory and History of 1957; and his Ultimate Foundations of Economic Science of 1962, Mises’s last book, appearing when he was already well past his eightieth birthday. And his works in the field of economics proper also invariably display the importance which Mises attached to the analysis of epistemological problems. Most characteristically, Human Action, his masterpiece, deals in its first hundred-odd pages exclusively with such problems, and the other nearly 800 pages of the book are permeated with epistemological considerations.

Quite in line with the tradition of Mises, then, the foundations of economics are also the subject of this chapter. I have set myself a twofold goal. First, I want to explain the solution which Mises advances regarding the problem of the ultimate foundation of economic science, i.e., his idea of a pure theory of action, or praxeology, as he himself terms it. And secondly, I want to demonstrate why Mises’s solution is much more than just an incontestable insight into the nature of economics and economic propositions.

It provides an insight that also enables us to understand the foundation on which epistemology ultimately rests. In fact, as the title of the chapter suggests, I want to show that it is praxeology which must be regarded as the very foundation of epistemology, and hence that Mises, aside from his great achievements as an economist, also contributed path-breaking insights regarding the justification of the entire enterprise of rationalist philosophy.⁴⁰

II

Let me turn to Mises’s solution. What is the logical status of typical economic propositions such as the law of marginal utility (that whenever the supply of a good whose units are regarded as of equal serviceability by a person increases by one additional unit, the value attached to this unit must decrease as it can only be employed as a means for the attainment of a goal that is considered less valuable than the least valuable goal previously satisfied by a unit of this good); or of the quantity theory of money (that whenever the quantity of money is increased while the demand for money to be held in cash reserve on hand is unchanged, the purchasing power of money will fall)?

In formulating his answer, Mises faced a double challenge. On the one hand, there was the answer offered by modern empiricism. The Vienna Ludwig von Mises knew was in fact one of the early centers of the empiricist movement: a movement which was then on the verge of establishing itself as the dominant academic philosophy of the Western world for several decades, and which to this very day shapes the image that an overwhelming majority of economists have of their own discipline.⁴¹

Empiricism considers nature and the natural sciences as its model. According to empiricism, the aforementioned examples of economic propositions have the same logical status as laws of nature: Like laws of nature they state hypothetical relationships between two or more events, essentially in the form of if-then statements. And like hypotheses of the natural sciences, the propositions of economics require continual testing vis-à-vis experience. A proposition regarding the relationship between economic events can never be validated once and for all with certainty. Instead, it is forever subject to the outcome of contingent, future experiences. Such experience might confirm the hypothesis. But this would not prove the hypothesis to be true, since the economic proposition would have used general terms (in philosophical terminology: universals) in its description of the related events, and thus would apply to an indefinite number of cases or instances, thereby always leaving room for possibly falsifying future experiences. All a confirmation would prove is that the hypothesis had not yet turned out wrong. On the other hand, the experience might falsify the hypothesis. This would surely prove that something was wrong with the hypothesis as it stood. But it would not prove that the hypothesized relationship between the specified events could never be observed. It would merely show that considering and controlling in one’s observations only what up to now had been actually accounted for and controlled, the relationship had not yet shown up. It cannot be ruled out, however, that it might show up as soon as some other circumstances have been controlled.

The attitude that this philosophy fuels and that has indeed become characteristic of most contemporary economists and their way of conducting their business is one of skepticism: the motto being “nothing can be known with certainty to be impossible in the realm of economic phenomena.” Even more precisely, since empiricism conceives of economic phenomena as objective data, extending in space and subject to quantifiable measurement—in strict analogy to the phenomena of the natural sciences—the peculiar skepticism of the empiricist economist may be described as that of a social engineer who will not guarantee anything.⁴²

The other challenge came from the side of the historicist school. Indeed, during Mises’s life in Austria and Switzerland, the historicist philosophy was the prevailing ideology of the German-speaking universities and their establishment. With the upsurge of empiricism this former prominence has been reduced considerably. But over roughly the last decade historicism has regained momentum among the Western world’s academia. Today it is with us everywhere under the names of hermeneutics, rhetoric, deconstructionism, and epistemological anarchism.⁴³

For historicism, and most conspicuously for its contemporary versions, the model is not nature but a literary text. Economic phenomena, according to the historicist doctrine, are not objective magnitudes that can be measured. Instead, they are subjective expressions and interpretations unfolding in history to be understood and interpreted by the economist just as a literary text unfolds before and is interpreted by its reader. As subjective creations, the sequence of their events follows no objective law. Nothing in the literary text, and nothing in the sequence of historical expressions and interpretations is governed by constant relations. Of course, certain literary texts actually exist, and so do certain sequences of historical events. But this by no means implies that anything had to happen in the order it did. It simply occurred. In the same way, however, as one can always invent different literary stories, history and the sequence of historical events, too, might have happened in an entirely different way. Moreover, according to historicism, and particularly visible in its modern hermeneutical version, the formation of these always contingently related human expressions and their interpretations is also not constrained by any objective law. In literary production anything can be expressed or interpreted concerning everything; and, along the same line, historical and economic events are whatever someone expresses or interprets them to be, and their description by the historian and economist is then whatever he expresses or interprets these past subjective events to have been.

The attitude that historicist philosophy generates is one of relativism. Its motto is “everything is possible.” Unconstrained by any objective law, for the historicist-hermeneutician history and economics, along with literary criticism, are matters of esthetics. And accordingly, his output takes on the form of disquisitions on what someone feels about what he feels was felt by somebody else—a literary form which we are only too familiar with, in particular in such fields as sociology and political science.⁴⁴

I trust that one senses intuitively that something is seriously amiss in both the empiricist as well as the historicist philosophies. Their epistemological accounts do not even seem to fit their own self-chosen models: nature on the one hand and literary texts on the other. And in any case, regarding economic propositions such as the law of marginal utility or the quantity theory of money their accounts seem to be simply wrong. The law of marginal utility certainly does not strike one as a hypothetical law subject forever for its validation to confirming or disconfirming experiences popping up here or there. And to conceive of the phenomena talked about in the law as quantifiable magnitudes seems to be nothing but ridiculous. Nor does the historicist interpretation seem to be any better. To think that the relationship between the events referred to in the quantity theory of money can be undone if one only wished to do so seems absurd. And the idea appears no less absurd that concepts such as money, demand for money, and purchasing power are formed without any objective constraints and refer merely to whimsical subjective creations. Instead, contrary to the empiricist doctrine, both examples of economic propositions appear to be logically true and to refer to events which are subjective in nature. And contrary to historicism, it would seem that what they state, then, could not possibly be undone in all of history and would contain conceptual distinctions which, while referring to subjective events, were nonetheless objectively constrained, and would incorporate universally valid knowledge.

Like most of the better known economists before him, Mises shares these intuitions.⁴⁵ Yet in quest of the foundation of economics, Mises goes beyond intuition. He takes on the challenge posed by empiricism and historicism in order to reconstruct systematically the basis on which these intuitions can be understood as correct and justified. He thereby does not want to help bring about a new discipline of economics. But in explaining what formerly had only been grasped intuitively, Mises goes far beyond what had ever been done before. In reconstructing the rational foundations of the economists’ intuitions, he assures us of the proper path for any future development in economics and safeguards us against systematic intellectual error.

Empiricism and historicism, Mises notes at the outset of his reconstruction, are self-contradictory doctrines.⁴⁶ The empiricist notion that all events, natural or economic, are only hypothetically related is contradicted by the message of this very basic empiricist proposition itself: For if this proposition were regarded as itself being merely hypothetically true, i.e., a hypothetically true proposition regarding hypothetically true propositions, it would not even qualify as an epistemological pronouncement. For it would then provide no justification whatsoever for the claim that economic propositions are not, and cannot be, categorically, or a priori true, as our intuition informs us they are. If, however, the basic empiricist premise were assumed to be categorically true itself, i.e., if we assume that one could say something a priori true about the way events are related, then this would belie its very own thesis that empirical knowledge must invariably be hypothetical knowledge, thus making room for a discipline such as economics claiming to produce a priori valid empirical knowledge. Further, the empiricist thesis that economic phenomena must be conceived of as observable and measurable magnitudes—analogous to those of the natural sciences—is rendered inconclusive, too, on its own account: For, obviously, empiricism wants to provide us with meaningful empirical knowledge when it informs us that our economic concepts are grounded in observations. And yet, the concepts of observation and measurement themselves, which empiricism must employ in claiming what it does, are both obviously not derived from observational experience in the sense that concepts such as hens and eggs or apples and pears are. One cannot observe someone making an observation or measurement. Rather, one must first understand what observations and measurements are in order to then be able to interpret certain observable phenomena as the making of an observation or the taking of a measurement. Thus, contrary to its own doctrine, empiricism is compelled to admit that there is empirical knowledge which is based on understanding—just as according to our intuitions economic propositions claim to be based on understanding—rather than on observations.⁴⁷

And regarding historicism, its self-contradictions are no less manifest. For if, as historicism claims, historical and economic events—which it conceives of as sequences of subjectively understood rather than observed events—are not governed by any constant, time-invariant relations, then this very proposition also cannot claim to say anything constantly true about history and economics. Instead, it would be a proposition with, so to speak, a fleeting truth value: it may be true now, if we wish it so, yet possibly false a moment later, in case we do not, with no one ever knowing anything about whether we do or do not. Yet, if this were the status of the basic historicist premise, it, too, would obviously not qualify as an epistemology. Historicism would not have given us any reason why we should believe any of it. If, however, the basic proposition of historicism were assumed to be invariantly true, then such a proposition about the constant nature of historical and economic phenomena would contradict its own doctrine denying any such constants. Furthermore, the historicist’s—and even more so its modern heir, the hermeneutician’s—claim that historical and economic events are mere subjective creations, unconstrained by any objective factors, is proven false by the very statement making it. For evidently, a historicist must assume this very statement to be meaningful and true; he must presume to say something specific about something, rather than merely uttering meaningless sounds like abracadabra. Yet if this is the case, then, clearly, his statement must be assumed to be constrained by something outside the realm of arbitrary subjective creations. Of course, I can say what the historicist says in English, German, or Chinese, or in any other language I wish, in so far as historic and economic expressions and interpretations may well be regarded as mere subjective creations. But whatever I say in whatever language I choose must be assumed to be constrained by some underlying propositional meaning of my statement, which is the same for any language, and exists completely independent of whatever the peculiar linguistic form may be in which it is expressed. And contrary to historicist belief, the existence of such a constraint is not such that one could possibly dispose of it at will. Rather, it is objective in that we can understand it to be the logically necessary presupposition for saying anything meaningful at all, as opposed to merely producing meaningless sounds. The historicist could not claim to say anything if it were not for the fact that his expressions and interpretations are actually constrained by laws of logic as the very presupposition of meaningful statements as such.⁴⁸

With such a refutation of empiricism and historicism, Mises notices, the claims of rationalist philosophy are successfully reestablished, and the case is made for the possibility of a priori true statements, as those of economics seem to be. Indeed, Mises explicitly regards his own epistemological investigations as the continuation of the work of western rationalist philosophy. With Leibniz and Kant he stands opposite the tradition of Locke and Hume.⁴⁹ He sides with Leibniz when he answers Locke’s famous dictum “nothing is in the intellect that has not previously been in the senses” with his equally famous one “except the intellect itself.” And he recognizes his task as a philosopher of economics as strictly analogous to that of Kant’s as a philosopher of pure reason, i.e., of epistemology. Like Kant, Mises wants to demonstrate the existence of true a priori synthetic propositions, or propositions whose truth values can be definitely established, even though in order to do so the means of formal logic are insufficient and observations are unnecessary.

My criticism of empiricism and historicism has proved the general rationalist claim. It has proved that we indeed do possess knowledge which is not derived from observation and yet is constrained by objective laws. In fact, our refutation of empiricism and historicism contains such a priori synthetic knowledge. Yet what about the constructive task of showing that the propositions of economics—such as the law of marginal utility and the quantity theory of money—qualify as this type of knowledge? In order to do so, Mises notices in accordance with the strictures traditionally formulated by rationalist philosophers, economic propositions must fulfill two requirements: First, it must be possible to demonstrate that they are not derived from observational evidence, for observational evidence can only reveal things as they happen to be; there is nothing in it that would indicate why things must be the way they are. Instead, economic propositions must be shown to be grounded in reflective cognition, in our understanding of ourselves as knowing subjects. And secondly this reflective understanding must yield certain propositions as self-evident material axioms. Not in the sense that such axioms would have to be self-evident in a psychological sense, that is, that one would have to be immediately aware of them or that their truth depends on a psychological feeling of conviction. On the contrary, like Kant before him, Mises very much stresses the fact that it is usually much more painstaking to discover such axioms than it is to discover some observational truth such as that the leaves of trees are green or that I am 6 foot 2 inches.⁵⁰ Rather, what makes them self-evident material axioms is the fact that no one can deny their validity without self-contradiction, because in attempting to deny them one already presupposes their validity.

Mises points out that both requirements are fulfilled by what he terms the axiom of action, i.e., the proposition that humans act, that they display intentional behavior.⁵¹ Obviously, this axiom is not derived from observation—there are only bodily movements to be observed but no such thing as actions—but stems instead from reflective understanding. And this understanding is indeed of a self-evident proposition. For its truth cannot be denied, since the denial would itself have to be categorized as an action. But is this not just plain trivial? And what has economics got to do with this? Of course, it had previously been recognized that economic concepts such as prices, costs, production, money, credit, etc., had something to do with the fact that there were acting people. But that all of economics could be grounded in and reconstructed based on such a trivial proposition and how, is certainly anything but clear. It is one of Mises’s greatest achievements to have shown precisely this: that there are insights implied in this psychologically speaking trivial axiom of action that were not themselves psychologically self-evident as well; and that it is these insights which provide the foundation for the theorems of economics as true a priori synthetic propositions.

It is certainly not psychologically evident that with every action an actor pursues a goal; and that whatever the goal may be, the fact that it was pursued by an actor reveals that he must have placed a relatively higher value on it than on any other goal of action that he could think of at the start of his action. It is not evident that in order to achieve his most highly valued goal an actor must interfere or decide not to interfere—which, of course, is also an intentional interference—at an earlier point in time in order to produce a later result; nor is it obvious that such interferences invariably imply the employment of some scarce means—at least those of the actor’s body, its standing room, and the time absorbed by the action. It is not self-evident that these means, then, must also have value for an actor—a value derived from that of the goal—because the actor must regard their employment as necessary in order to effectively achieve the goal; and that actions can only be performed sequentially, always involving a choice, i.e., taking up that one course of action which at some given time promises the most highly valued results to the actor and excluding at the same time the pursual of other, less highly valued goals. It is not automatically clear that as a consequence of having to choose and give preference to one goal over another—of not being able to realize all goals simultaneously—each and every action implies the incurrence of costs, i.e., forsaking the value attached to the most highly ranking alternative goal that cannot be realized or whose realization must be deferred, because the means necessary to attain it are bound up in the production of another, even more highly valued goal. And lastly, it is not evident that at its starting point every goal of action must be considered worth more to the actor than its cost and capable of yielding a profit, i.e., a result whose value is ranked higher than that of the foregone opportunity, and yet that every action is also invariably threatened by the possibility of a loss if an actor finds, in retrospect, that contrary to his expectations the actually achieved result in fact has a lower value than the relinquished alternative would have had.

All of these categories which we know to be the very heart of economics—values, ends, means, choice, preference, cost, profit and loss—are implied in the axiom of action. Like the axiom itself, they are not derived from observation. Rather, that one is able to interpret observations in terms of such categories requires that one already knows what it means to act. No one who is not an actor could ever understand them, as they are not “given,” ready to be observed, but observational experience is cast in these terms as it is construed by an actor. And while they and their interrelations were not obviously implied in the action axiom, once it has been made explicit that they are implied, and how, one no longer has any difficulty recognizing them as being a priori true in the same sense as the axiom itself is. For any attempt to disprove the validity of what Mises has reconstructed as implied in the very concept of action would have to be aimed at a goal, requiring means, excluding other courses of action, incurring costs, subjecting the actor to the possibility of achieving or not achieving the desired goal and so leading to a profit or a loss. Thus, it is manifestly impossible to ever dispute or falsify the validity of Mises’s insights. In fact, a situation in which the categories of action would cease to have a real existence could itself never be observed or spoken of, since to make an observation and to speak are themselves actions.

All true economic propositions, and this is what praxeology is all about and what Mises’s great insight consists of, can be deduced by means of formal logic from this incontestably true material knowledge regarding the meaning of action and its categories. More precisely all true economic theorems consist of (a) an understanding of the meaning of action, (b) a situation or situational change—assumed to be given or identified as being given—and described in terms of action-categories, and (c) a logical deduction of the consequences—again in terms of such categories—which are to result for an actor from this situation or situational change. The law of marginal utility, for instance,⁵² follows from our indisputable knowledge of the fact that every actor always prefers what satisfies him more over what satisfies him less, plus the assumption that he is faced with an increase in the supply of a good (a scarce mean) whose units he regards as of equal serviceability, by one additional unit. From this it follows with logical necessity that this additional unit can then only be employed as a means for the removal of an uneasiness that is deemed less urgent than the least valuable goal previously satisfied by a unit of such a good. Provided there is no flaw in the process of deduction, the conclusions which economic theorizing yields, no different in the case of any other economic proposition from the case of the law of marginal utility, must be valid a priori. These propositions’ validity ultimately goes back to nothing but the indisputable axiom of action. To think, as empiricism does, that these propositions require continual empirical testing for their validation is absurd, and a sign of outright intellectual confusion. And it is no less absurd and confused to believe, as historicism does, that economics has nothing to say about constant and invariable relations but merely deals with historically accidental events. To say so meaningfully is to prove such a statement wrong, as saying anything meaningful at all already presupposes acting and a knowledge of the meaning of the categories of action.

III

This will suffice here as an explanation of Mises’s answer regarding the quest for the foundations of economics. I shall now turn to my second goal: the explanation of why and how praxeology also provides the foundation for epistemology Mises had been aware of this and he was convinced of the great importance of this insight for rationalist philosophy. Yet Mises did not treat the matter in a systematic fashion. There are no more than a few brief remarks concerning this problem, interspersed throughout his massive body of writing.⁵³ Thus, in the following I must try to break new ground.

I shall begin my explanation by introducing a second a priori axiom and clarifying its relation to the axiom of action. Such an understanding is the key to solving our problem. The second axiom is the so-called “a priori of argumentation,” which states that humans are capable of argumentation and hence know the meaning of truth and validity.⁵⁴ As in the case of the action axiom, this knowledge is not derived from observation: there is only verbal behavior to be observed and prior reflective cognition is required in order to interpret such behavior as meaningful arguments. And the validity of the axiom, like that of the action axiom, is indisputable. It is impossible to deny that one can argue, as the very denial would itself be an argument. In fact, one could not even silently say to oneself “I cannot argue” without thereby contradicting oneself. One cannot argue that one cannot argue. Nor can one dispute knowing what it means to make a truth or validity claim without implicitly claiming the negation of this proposition to be true.

It is not difficult to detect that both a priori axioms—of action and argumentation—are intimately related. On the one hand, actions are more fundamental than argumentations with whose existence the idea of validity emerges, as argumentation is only a subclass of action. On the other hand, to recognize what has just been recognized regarding action and argumentation and their relation to each other requires argumentation, and so, in this sense, argumentation must be considered more fundamental than action: without argumentation nothing could be said to be known about action. But then, as it is in argumentation that the insight is revealed that—while it might not be known to be so prior to any argumentation—in fact the possibility of argumentation presupposes action in that validity claims can only be explicitly discussed in the course of an argumentation if the individuals doing so already know what it means to act and to have knowledge implied in action—both the meaning of action in general and argumentation in particular must be thought of as logically necessary interwoven strands of a priori knowledge.

What this insight into the interrelation between the a priori of action and the a priori of argumentation suggests is the following: Traditionally, the task of epistemology has been conceived of as that of formulating what can be known to be true a priori and also what can be known a priori not to be the subject of a priori knowledge. Recognizing, as we have just done, that knowledge claims are raised and decided upon in the course of argumentation and that this is undeniably so, one can now reconstruct the task of epistemology more precisely as that of formulating those propositions which are argumentatively indisputable in that their truth is already implied in the very fact of making one’s argument and so cannot be denied argumentatively; and to delineate the range of such a priori knowledge from the realm of propositions whose validity cannot be established in this way but require additional, contingent information for their validation, or that cannot be validated at all and so are mere metaphysical statements in the pejorative sense of the term metaphysical.

Yet what is implied in the very fact of arguing? It is to this question that our insight into the inextricable interconnection between the a priori of argumentation and that of action provides an answer: On a very general level, it cannot be denied argumentatively that argumentation presupposes action and that arguments, and the knowledge embodied in them, are those of actors. And more specifically, it cannot then be denied that knowledge itself is a category of action; that the structure of knowledge must be constrained by the peculiar function which knowledge fulfills within the framework of action categories; and that the existence of such structural constraints can never be disproved by any knowledge whatsoever.

It is in this sense that the insights contained in praxeology must be regarded as providing the foundations of epistemology Knowledge is a category quite distinct from those that I have explained earlier—from ends and means. The ends which we strive to attain through our actions, and the means which we employ in order to do so, are both scarce values. The values attached to our goals are subject to consumption and are exterminated and destroyed in consumption and thus must forever be produced anew. And the means employed must be economized, too. Not so, however, with respect to knowledge—regardless of whether one considers it a means or an end in itself. Of course, the acquisition of knowledge requires scarce means—at least one’s body and time. Yet once knowledge is acquired, it is no longer scarce. It can neither be consumed, nor are the services that it can render as a means subject to depletion. Once there, it is an inexhaustible resource and incorporates an everlasting value provided that it is not simply forgotten.⁵⁵ Yet knowledge is not a free good in the same sense that air, under normal circumstances, is a free good. Instead, it is a category of action. It is not only a mental ingredient of each and every action, quite unlike air, but more importantly, knowledge, and not air, is subject to validation, which is to say that it must prove to fulfill a positive function for an actor within the invariant constraints of the categorical framework of actions. It is the task of epistemology to clarify what these constraints are and what one can thus know about the structure of knowledge as such.

While such recognition of the praxeological constraints on the structure of knowledge might not immediately strike one as in itself of great significance, it does have some highly important implications. For one thing, in light of this insight one recurring difficulty of rationalist philosophy finds its answer. It has been a common quarrel with rationalism in the Leibniz-Kant tradition that it seemed to imply some sort of idealism. Realizing that a priori true propositions could not possibly be derived from observations, rationalism answered the question how a priori knowledge could then be possible by adopting the model of an active mind, as opposed to the empiricist model of a passive, mirror-like mind in the tradition of Locke and Hume. According to rationalist philosophy, a priori true propositions had their foundation in the operation of principles of thinking which one could not possibly conceive of as operating otherwise; they were grounded in categories of an active mind. Now, as empiricists were only too eager to point out, the obvious critique of such a position is, that if this were indeed the case, it could not be explained why such mental categories should fit reality Rather, one would be forced to accept the absurd idealistic assumption that reality would have to be conceived of as a creation of the mind, in order to claim that a priori knowledge could incorporate any information about the structure of reality And clearly, such an assertion seemed to be justified when faced with programmatic statements of rationalist philosophers such as the following by Kant: “So far it has been assumed that our knowledge had to conform to reality” instead it should be assumed “that observational reality should conform to our mind.”⁵⁶

Recognizing knowledge as being structurally constrained by its role in the framework of action categories provides the solution to such a complaint. For as soon as this is realized, all idealistic suggestions of rationalist philosophy disappear, and an epistemology claiming that a priori true propositions exist becomes a realistic epistemology instead. Understood as constrained by action categories, the seemingly unbridgeable gulf between the mental on the one hand and the real, outside physical world on the other is bridged. So constrained, a priori knowledge must be as much a mental thing as a reflection of the structure of reality, since it is only through actions that the mind comes into contact with reality, so to speak. Acting is a cognitively guided adjustment of a physical body in physical reality. And thus, there can be no doubt that a priori knowledge, conceived of as an insight into the structural constraints imposed on knowledge qua knowledge of actors, must indeed correspond to the nature of things. The realistic character of such knowledge would manifest itself not only in the fact that one could not think it to be otherwise, but in the fact that one could not undo its truth.

Yet there are more specific implications involved in recognizing the praxeological foundations of epistemology—apart from the general one that in substituting the model of the mind of an actor acting by means of a physical body for the traditional rationalist model of an active mind a priori knowledge immediately becomes realistic knowledge (so realistic indeed that it can be understood as being literally not undoable). More specifically, in light of this insight decisive support is given to those deplorably few rationalist philosophers who—against the empiricist Zeitgeist—stubbornly maintain on various philosophical fronts that a priori true propositions about the real world are possible.⁵⁷ Moreover, in light of the recognition of praxeological constraints on the structure of knowledge these various rationalist endeavors become systematically integrated into one, unified body of rationalist philosophy.

In explicitly understanding knowledge as displayed in argumentation as a peculiar category of action, it becomes clear immediately why the perennial rationalist claim that the laws of logic—beginning here with the most fundamental ones, i.e., of propositional logic and of Junctors (“and,” “or,” “if-then,” “not”) and Quantors (“there is,” “all,” “some”)—are a priori true propositions about reality and not mere verbal stipulations regarding the transformation rules of arbitrarily chosen signs, as empiricist-formalists would have it, is indeed correct. They are as much laws of thinking as of reality, because they are laws that have their ultimate foundation in action and could not be undone by any actor. In each and every action, an actor identifies some specific situation and categorizes it one way rather than another in order to be able to make a choice. It is this which ultimately explains the structure of even the most elementary propositions (like “Socrates is a man”) consisting of a proper name or some identifying expression for the naming or identifying of something, and a predicate to assert or deny some specific property of the named or identified object; and which explains the cornerstones of logic: the laws of identity and contradiction. And it is this universal feature of action and choosing which also explains our understanding of the categories “there is,” “all” and, by implication, “some,” as well as “and,” “or,” “if-then” and “not.”⁵⁸ One can say, of course, that something can be “a” and “non-a” at the same time, or that “and” means this rather than something else. But one cannot undo the law of contradiction; and one cannot undo the real definition of “and.” For simply by virtue of acting with a physical body in physical space we invariably affirm the law of contradiction and invariably display our true constructive knowledge of the meaning of “and” and “or.”

Similarly, the ultimate reason for arithmetic’s being an a priori and yet empirical discipline, as rationalists have always understood it, now also becomes discernible. The prevailing empiricist-formalist orthodoxy conceives of arithmetic as the manipulation of arbitrarily defined signs according to arbitrarily stipulated transformation rules, and thus as entirely void of any empirical meaning. For this view, which evidently makes arithmetic nothing but play, however skillful it might be, the successful applicability of arithmetic in physics is an intellectual embarrassment. Indeed, empiricist-formalists would have to explain away this fact as simply being a miraculous event. That it is no miracle, however, becomes apparent once the praxeological or—to use here the terminology of the most notable rationalist philosopher-mathematician Paul Lorenzen and his school—the operative or constructivist character of arithmetic is understood. Arithmetic and its character as an a priori-synthetic intellectual discipline is rooted in our understanding of repetition, the repetition of action. More precisely, it rests on our understanding the meaning of “do this—and do this again, starting from the present result.” And arithmetic then deals with real things: with constructed or constructively identified units of something. It demonstrates what relations are to hold between such units because of the fact that they are constructed according to the rule of repetition. As Paul Lorenzen has demonstrated in detail, not all of what presently poses as mathematics can be constructively founded—and those parts, then, should of course be recognized for what they are: epistemologically worthless symbolic games. But all of the mathematical tools that are actually employed in physics, i.e., the tools of classical analysis, can be constructively derived. They are not empirically void symbolisms, but true propositions about reality. They apply to everything insofar as it consists of one or more distinct units, and insofar as these units are constructed or identified as units by a procedure of “do it again, construct or identify another unit by repeating the previous operation.”⁵⁹ Again, one can say, of course, that 2 plus 2 is sometimes 4 but sometimes 2 or 5 units, and in observational reality, for lions plus lambs or for rabbits, this may even be true,⁶⁰ but in the reality of action, in identifying or constructing those units in repetitive operations, the truth that 2 plus 2 is never anything but 4 could not possibly be undone.

Further, the old rationalist claims that geometry, that is, Euclidean geometry is a priori and yet incorporates empirical knowledge about space becomes supported, too, in view of our insight into the praxeological constraints on knowledge. Since the discovery of non-Euclidean geometries and in particular since Einstein’s relativistic theory of gravitation, the prevailing position regarding geometry is once again empiricist and formalist. It conceives of geometry as either being part of empirical, aposteriori physics, or as being empirically meaningless formalisms. Yet that geometry is either mere play, or forever subject to empirical testing seems to be irreconcilable with the fact that Euclidean geometry is the foundation of engineering and construction, and that nobody there ever thinks of such propositions as only hypothetically true.⁶¹ Recognizing knowledge as praxeologically constrained explains why the empiricist-formalist view is incorrect and why the empirical success of Euclidean geometry is no mere accident. Spatial knowledge is also included in the meaning of action. Action is the employment of a physical body in space. Without acting there could be no knowledge of spatial relations, and no measurement. Measuring is relating something to a standard. Without standards, there is no measurement; and there is no measurement, then, which could ever falsify the standard. Evidently, the ultimate standard must be provided by the norms underlying the construction of bodily movements in space and the construction of measurement instruments by means of one’s body and in accordance with the principles of spatial constructions embodied in it. Euclidean geometry, as again Paul Lorenzen in particular has explained, is no more and no less than the reconstruction of the ideal norms underlying our construction of such homogeneous basic forms as points, lines, planes and distances, which are in a more or less perfect but always perfectible way incorporated or realized in even our most primitive instruments of spatial measurements such as a measuring rod. Naturally, these norms and normative implications cannot be falsified by the result of any empirical measurement. On the contrary, their cognitive validity is substantiated by the fact that it is they which make physical measurements in space possible. Any actual measurement must already presuppose the validity of the norms leading to the construction of one’s measurement standards. It is in this sense that geometry is an a priori science; and that it must simultaneously be regarded as an empirically meaningful discipline, because it is not only the very precondition for any empirical spatial description, it is also the precondition for any active orientation in space.⁶²

In view of the recognition of the praxeological character of knowledge, these insights regarding the nature of logic, arithmetic and geometry become integrated and embedded into a system of epistemological dualism.⁶³ The ultimate justification for this dualist position, i.e., the claim that there are two realms of intellectual inquiry that can be understood a priori as requiring categorically distinct methods of treatment and analysis, also lies in the praxeological nature of knowledge. It explains why we must differentiate between a realm of objects which is categorized causally and a realm that is categorized teleologically instead.

I have already briefly indicated during my discussion of praxeology that causality is a category of action. The idea of causality that there are constant, time-invariantly operating causes which allow one to project past observations regarding the relation of events into the future is something (as empiricism since Hume has noticed) which has no observational basis whatsoever. One cannot observe the connecting link between observations. Even if one could, such an observation would not prove it to be a time-invariant connection. Instead, the principle of causality must be understood as implied in our understanding of action as an interference with the observational world, made with the intent of diverting the “natural” course of events in order to produce a different, prefered state of affairs, i.e., of making things happen that otherwise would not happen, and thus presupposes the notion of events which are related to each other through time-invariantly operating causes. An actor might err with respect to his particular assumptions about which earlier interference produced which later result. But successful or not, any action, changed or unchanged in light of its previous success or failure, presupposes that there are constantly connected events as such, even if no particular cause for any particular event can ever be preknown to any actor. Without such an assumption it would be impossible to ever categorize two or more observational experiences as falsifying or confirming each other rather than interpreting them as logically incommensurable events. Only because the existence of time-invariantly operating causes as such is already assumed can one ever encounter particular instances of confirming or disconfirming observational evidence, or can there ever be an actor who can learn anything from past experience by classifying his actions as successful and confirming some previous knowledge, or unsuccessful and disconfirming it. It is simply by virtue of acting and distinguishing between successes and failures that the a priori validity of the principle of causality is established; even if one tried, one could not successfully refute its validity.⁶⁴

In so understanding causality as a necessary presupposition of action, it is also immediately implied that its range of applicability must then be delineated a priori from that of the category of teleology Indeed, both categories are strictly exclusive and complementary. Action presupposes a causally structured observational reality, but the reality of action which we can understand as requiring such structure, is not itself causally structured. Instead, it is a reality that must be categorized teleologically, as purpose-directed, meaningful behavior. In fact, one can neither deny nor undo the view that there are two categorically different realms of phenomena, since such attempts would have to presuppose causally related events qua actions that take place within observational reality, as well as the existence of intentionally rather than causally related phenomena in order to interpret such observational events as meaning to deny something. Neither a causal, nor a teleological monism could be justified without running into an open contradiction: physically stating either position, and claiming to say something meaningful in so doing, the case is in fact made for an indisputable complementarity of both, a realm of causal and teleological phenomena.⁶⁵

Everything which is not an action must necessarily be categorized causally. There is nothing to be known a priori about this range of phenomena except that it is structured causally—and that it is structured according to the categories of propositional logic, arithmetic and geometry.⁶⁶ Everything else there is to know about this range of phenomena must be derived from contingent observations and thus represents aposteriori knowledge. In particular, all knowledge about two or more specific observational events being causally related or not is aposteriori knowledge. Obviously, the range of phenomena described in this way coincides (more or less) with what is usually considered to be the field of the empirical natural sciences.

In contrast, everything that is an action must be categorized teleologically This realm of phenomena is constrained by the laws of logic and arithmetic, too. But it is not constrained by the laws of geometry as incorporated in our instruments of measuring spatially extending objects, because actions do not exist apart from subjective interpretations of observable things; and so they must be identified by reflective understanding rather than spatial measurements. Nor are actions causally connected events, but events that are connected meaningfully within a categorical framework of means and ends.

One can not know a priori what the specific values, choices and costs of some actor are or will be. This would fall entirely into the province of empirical, aposteriori knowledge. In fact, which particular action an actor is going to undertake would depend on his knowledge regarding the observational reality and/or the reality of other actors’ actions. And it would be manifestly impossible to conceive of such states of knowledge as predictable on the basis of time-invariantly operating causes. A knowing actor cannot predict his future knowledge before he has actually acquired it, and he demonstrates, simply by virtue of distinguishing between successful and unsuccessful predictions, that he must conceive of himself as capable of learning from unknown experiences in as yet unknown ways. Thus, knowledge regarding the particular course of actions is only aposteriori. And since such knowledge would have to include the actor’s own knowledge—as a necessary ingredient of every action whose every change can have an influence on a particular action being chosen—teleological knowledge must also necessarily be reconstructive, or historical knowledge. It would only provide ex-post explanations which would have no systematic bearing on the prediction of future actions, because, in principle, future states of knowledge could never be predicted on the basis of constantly operating empirical causes. Obviously, such a delineation of a branch of aposteriori and reconstructive science of action fits the usual description of such disciplines as history and sociology.⁶⁷

What is known to be true a priori regarding the field of action, and what would then have to constrain any historical or sociological explanation is this: For one thing, any such explanation, which essentially would have to reconstruct an actor’s knowledge, would invariably have to be a reconstruction in terms of knowledge of ends and means, of choices and costs, of profits and losses and so on. And secondly, since these are evidently the categories of praxeology as conceived of by Mises, any such explanation must also be constrained by the laws of praxeology. And since these laws are, as I have already explained, a priori laws, they must also operate as logical constraints on any future course of action. They are valid independent of any specific state of knowledge that an actor might have acquired, simply by virtue of the fact that whatever this state might be, it must be described in terms of action categories. And as referring to actions as such, the laws of praxeology must then be coextensive with all the predictive knowledge there can be in the field of the science of action. In fact, ignoring for the moment that the status of geometry as an a priori science was ultimately grounded in our understanding of action and in so far praxeology would have to be regarded as the more fundamental cognitive discipline, the peculiar role of praxeology proper within the entire system of epistemology can be understood as somewhat analogous to that of geometry Praxeology is for the field of action what Euclidean geometry is for the field of observations (non-actions). As the geometry incorporated in our measuring instruments constrains the spatial structure of observational reality, so praxeology constrains the range of things that can possibly be experienced in the field of actions.⁶⁸

IV

In so establishing the place of praxeology proper, I have come full circle in outlining the system of rationalist philosophy as ultimately grounded in the action axiom. It has been my goal here to reaffirm Mises’s claim that economics is praxeology; that the case for praxeology is an indisputable one; and that empiricist or historicist-hermeneuticist interpretations of economics are self-contradictory doctrines. And it has been my objective to indicate that the Misesian insight into the nature of praxeology also provides the very foundation on which traditional rationalist philosophy can be successfully reconstructed, and systematically integrated.

For the rationalist philosopher this would seem to imply that he should take account of praxeology. For it is precisely the insight into the praxeological constraints on the structure of knowledge which provides the missing link in his intellectual defense against skepticism and relativism. For the economist in the tradition of Mises it means, I claim, that he should explicitly come to recognize his place within the wider tradition of western rationalism; and that he should learn to incorporate the insights provided by this tradition in order to construct an even more impressive and profound case for praxeology and Austrian economics than the one made by the great Mises himself.

This essay is from Hans-Hermann Hoppe, The Economics and Ethics of Private Property (Kluwer Academic Publishers in 1993), pp. 141–64 and it is reprinted here with permission of Kluwer Academic Publishers.

⁴⁰See on the following also my Kritik der kausalwissenschaftlichen Sozialforschung. Untersuchungen zur Grundlegung von Soziologie und Ökonomie; idem, “Is Research Based on Causal Scientific Principles Possible in the Social Sciences?,” chapter 7); idem, “In Defense of Extreme Rationalism.”

⁴¹On the Vienna Circle see V. Kraft, Der Wiener Kreis (Vienna: Springer, 1968); for empiricist-positivist interpretations of economics see such representative works as Terence W Hutchison, The Significance and Basic Postulates of Economic Theory [Hutchison, an adherent of the Popperian variant of empiricism, has since become much less enthusiastic about the prospects of a Popperized economics—see, for instance, his Knowledge and Ignorance in Economics—yet he still sees no alternative but to cling to Popper’s falsificationism anyway.]; Milton Friedman, “The Methodology of Positive Economics,” in idem, Essays in Positive Economics; Mark Blaug, The Methodology of Economics; a positivist account by a participant in Mises’s Privat Seminar in Vienna is F. Kaufmann, Methodology of the Social Sciences; the dominance of empiricism in economics is documented by the fact that there is probably not a single textbook, which does not explicitly classify economics as—what else?—an empirical (a posteriori) science.

⁴²On the relativistic consequences of empiricism-positivism see also Hoppe, A Theory of Socialism and Capitalism (Boston: Kluwer Academic Publishers, 1989), chapter 6; idem, “The Intellectual Cover for Socialism.”

⁴³See Ludwig von Mises, The Historical Setting of the Austrian School of Economics (Auburn, Ala.:Ludwig von Mises Institute, 1984); idem, Erinnerungen (Stuttgart: Gustav Fischer, 1978); idem, Theory and History, chapter 10; Murray N. Rothbard, Ludwig von Mises: Scholar, Creator, Hero (Auburn, Ala.: Ludwig von Mises Institute, 1988); for a critical survey of historicist ideas see also Karl Popper, The Poverty of Historicism; for a representative of the older version of a historicist interpretation of economics see Werner Sombart, Die drei Nationalökonomien (Munich: Duncker & Humblot, 1930); for the modern, hermeneutical twist Donald McCloskey, The Rhetoric of Economics (Madison: University of Wisconsin Press, 1985); Ludwig Lachmann, “From Mises to Shackle: An Essay on Austrian Economics and the Kaleidic Society,” Journal of Economic Literature (1976).

⁴⁴On the extreme relativism of historicism-hermeneutics see Hoppe, “In Defense of Extreme Rationalism”; Murray N. Rothbard, “The Hermeneutical Invasion of Philosophy and Economics,” Review of Austrian Economics (1988); Henry Veatch, “Deconstruction in Philosophy: Has Rorty Made it the Denouement of Contemporary Analytical Philosophy,” Review of Metaphysics (1985); Jonathan Barnes, “A Kind of Integrity” Austrian Economics Newsletter (Summer 1987); David Gordon, Hermeneutics vs. Austrian Economics (Auburn, Ala.: Ludwig von Mises Institute, Occasional Paper Series, 1987); for a brilliant critique of contemporary sociology see St. Andreski, Social Science as Sorcery (New York: St. Martin’s Press, 1973).

⁴⁵Regarding the epistemological views of such predecessors as J. B. Say, Nassau W. Senior, J. E. Cairnes, John Stuart Mill, Carl Menger, and Friedrich von Wieser see Ludwig von Mises, Epistemological Problems of Economics, pp. 17–23; also Murray N. Rothbard, “Praxeology: The Methodology of Austrian Economics,” in Edwin Dolan, ed., The Foundations of Modern Austrian Economics (Kansas City: Sheed and Ward, 1976).

⁴⁶In addition to Mises’s works cited at the outset of this chapter and the literature mentioned in note 40, see Murray N. Rothbard, Individualism and the Philosophy of the Social Sciences (San Francisco: Cato Institute, 1979); for a splendid philosophical critique of empiricist economics see Hollis and Nell, Rational Economic Man; as particularly valuable general defenses of rationalism as against empiricism and relativism—without reference to economics, however,—see Blanshard, Reason and Analysis; Kambartel, Erfahrung und Struktur.

⁴⁷For an elaborate defense of epistemological dualism see also Apel, Transformation der Philosophie, 2 vols, and Habermas, Zur Logik der Sozialwissenschaften.

⁴⁸See on this in particular Hoppe, “In Defense of Extreme Rationalism.”

⁴⁹See Mises, The Ultimate Foundation of Economic Science, p. 12.

⁵⁰See Kant, Kritik der reinen Vernunft, p. 45; Mises, Human Action, p. 38.

⁵¹On the following see in particular Mises, Human Action, chapter 4; Murray N. Rothbard, Man, Economy, and State (Los Angeles: Nash, 1962), chapter 1.

⁵²On the law of marginal utility see Mises, Human Action, pp. 119–27 and Rothbard, Man, Economy, and State, pp. 268–71.

⁵³Mises writes: “Knowledge is a tool of action. Its function is to advise man how to proceed in his endeavor to remove uneasiness. . .. The category of action is the fundamental category of human knowledge. It implies all the categories of logic and the category of regularity and causality. It implies the category of time and that of value. . . . In acting, the mind of the individual sees itself as different from its environment, the external world, and tries to study this environment in order to influence the course of events happening in it” (The Ultimate Foundation of Economic Science, pp. 35–36). Or: “Both, apriori thinking and reasoning on the one hand and human action on the other, are manifestations of the mind. . . . Reason and action are congeneric and homogeneous, two aspects of the same phenomenon” (ibid., p.42). Yet he leaves the matter more or less at this and concludes that “it is not the scope of praxeology to investigate the relation of thinking and action” (Human Action, p. 25).

⁵⁴On the a priori of argumentation see also K. O. Apel, Transformation der Philosophie, vol. 2.

⁵⁵On this fundamental difference between economic, i.e., scarce means and knowledge, see also Mises, Human Action, pp. 128, 661.

⁵⁶Immanuel Kant, Kritik der reinen Vernunft, p. 25. Whether or not such an interpretation of Kant’s epistemology is indeed correct is, of course, a very different matter. Clarifying this problem is, however, of no concern here. For an activist or constructivist interpretation of Kantian philosophy see F. Kambartel, Erfahrung und Struktur, chapter 3; also Hoppe, Handeln und Erkennen (Bern: Lang, 1976).

⁵⁷In addition to the works mentioned in note 46 see Brand Blanshard, The Nature of Thought (London: Allen and Unwin, 1921); M. Cohen, Reason and Nature (New York: Harcourt, Brace, 1931); idem, Preface to Logic (New York: Holt, 1944); A. Pap, Semantics and Necessary Truth (New Haven: Yale University Press, 1958); S. Kripke, “Naming and Necessity,” in D. Davidson and G. Harman, eds., Semantics of Natural Language (New York: Reidel, 1972); H. Dingler, Die Ergreifung des Wirklichen (Frankfurt/M.: Suhrkamp, 1969); idem, Aufbau der exakten Fundamentalwissenschaft (Munich: Eidos, 1964); W Kamlah and P. Lorenzen, Logische Propädeutik Mannheim: (Mannheim: Bibliographisches Institut, 1968); P. Lorenzen, Methodisches Denken (Frankfurt/M.: Suhrkamp, 1968); idem, Normative Logic and Ethics (Mannheim: Bibliographisches Institut, 1969); K. O. Apel, Transformation der Philosophie.

⁵⁸On rationalist interpretations of logic see Blanshard, Reason and Analysis, chapters 6, 10; P. Lorenzen, Einführung in die operative Logik und Mathematik (Frankfurt/M.: Akademische Verlagsgesellschaft, 1970); K. Lorenz, Elemente der Sprachkritik (Frankfurt/M.: Suhrkamp, 1970); idem, “Die dialogische Rechtfertigung der effektiven Logik,” in: F. Kambartel and J. Mittelstrass, eds., Zum normativen Fundament der Wissenschaft (Frankfurt/M.: Athenäum, 1973).

On the propositional character of language and experience, in particular, see W Kamlah and P. Lorenzen, Logische Propädeutik, chapter 1; P. Lorenzen, Normative Logic and Ethics, chapter 1. Lorenzen writes: “I call a usage a convention if I know of another usage which I could accept instead. . . . However, I do not know of another behavior which could replace the use of elementary sentences. If I did not accept proper names and predicators, I would not know how to speak at all. . . . Each proper name is a convention . . . but to use proper names at all is not a convention: it is a unique pattern of linguistic behavior. Therefore, I am going to call it ‘logical’. The same is true with predicators. Each predicator is a convention. This is shown by the existence of more than one natural language. But all languages use predicators” (ibid., p. 16). See also J. Mittelstrass, “Die Wiederkehr des Gleichen,” Ratio (1966).

On the law of identity and contradiction, in particular, see B. Blanshard, Reason and Analysis, pp. 276ff, 423ff.

On a critical evaluation of 3- or more-valued logics as either meaningless symbolic formalisms or as logically presupposing an understanding of the traditional two-valued logic see W Stegmüller, Hauptströmungen der Gegenwartsphilosophie vol. 2 (Stuttgart: Kröner, 1975), pp. 182–91; B. Blanshard, Reason and Analysis, pp. 269–75. Regarding, for instance, the many-valued or open-textured logic, proposed by F. Waismann, Blanshard notes: “We can only agree with Dr. Waismann—and with Hegel—that the black-and-white distinctions of formal logic are quite inadequate to living thought. But why should one say, as Dr. Waismann does, that in adopting a more differentiated logic one is adopting an alternative system which is incompatible with black-and-white logic? What he has actually done is to recognize a number of gradations within the older meaning of the word ‘not’. We do not doubt that such gradations are there, and indeed as many more as he cares to distinguish. But a refinement of the older logic is not an abandonment of it. It is still true that the colour I saw yesterday was either a determinate shade of yellow or not, even though the ‘not’ may cover a multitude of approximations, and even though I shall never know which was the shade I saw” (ibid., pp. 273–74).

⁵⁹On a rationalist interpretation of arithmetic see Blanshard, Reason and Analysis, pp. 427–31; on the constructivist foundation of arithmetic, in particular, see Lorenzen, Einführung in die operative Logik und Mathematik; idem, Methodisches Denken, chapters 6, 7; idem, Normative Logic and Ethics, chapter 4; on the constructivist foundation of classical analysis see P. Lorenzen, Differential und Integral: Eine konstruktive Einführung in die klassische Analysis (Frankfurt/M.: Akademische Verlagsgesellschaft, 1965); for a brilliant general critique of mathematical formalism see Kambartel, Erfahrung und Struktur, chapter 6, esp. pp. 236–42; on the irrelevance of the famous Gödel-theorem for a constructively founded arithmetic see P. Lorenzen, Metamathematik (Mannheim: Bibliographisches Institut, 1962); also Ch. Thiel, “Das Begründungsproblem der Mathematik und die Philosophie,” in F. Kambartel and J. Mittelstrass, eds., Zum normativen Fundament der Wissenschaft, esp. pp. 99–101. K. Gödel’s proof—which, as a proof, incidentally supports rather than undermines the rationalist claim of the possibility a priori knowledge—only demonstrates that the early formalist Hilbert program cannot be successfully carried through, because in order to demonstrate the consistency of certain axiomatic theories one must have a metatheory with even stronger means than those formalized in the object-theory itself. Interestingly enough, the difficulties of the formalist program had led the old Hilbert already several years before Gödel’s proof of 1931 to recognize the necessity of reintroducing a substantive interpretation of mathematics à la Kant, which would give its axioms a foundation and justification that was entirely independent of any formal consistency proofs. See Kambartel, Erfahrung und Struktur, pp. 185–87.

⁶⁰Examples of this kind are used by Karl Popper in order to “refute” the rationalist idea of rules of arithmetic being laws of reality. See Karl Popper, Conjectures and Refutations (London: Routledge and Kegan Paul, 1969), p. 211.

⁶¹See on this also Mises, The Ultimate Foundation of Economic Science, pp. 12–14.

⁶²On the aprioristic character of Euclidean geometry see Lorenzen, Methodisches Denken, chapters 8 and 9; idem, Normative Logic and Ethics, chapter 5; H. Dingler, Die Grundlagen der Geometrie (Stuttgart: Enke, 1933); on Euclidean geometry as a necessary presupposition of objective, i.e., intersubjectively communicable, measurements and in particular of any empirical verification of non-Euclidean geometries (after all, the lenses of the telescopes which one uses to confirm Einstein’s theory regarding the non-Euclidean structure of physical space must themselves be constructed according to Euclidean principles) see Kambartel, Erfahrung und Struktur, pp. 132–33; P. Janich, Die Protophysik der Zeit (Mannheim: Bibliographisches Institut, 1969), pp. 45–50; idem, “Eindeutigkeit, Konsistenz und methodische Ordnung,” in F. Kambartel and J. Mittelstrass, eds., Zum normativen Fundament der Wissenschaft.

Following the lead of Hugo Dingler, Paul Lorenzen and other members of the so-called Erlangen school have worked out a system of protophysics, which contains all aprioristic presuppositions of empirical physics, including, apart from geometry, also chronometry and hylometry (i.e., classical mechanics without gravitation, or “rational” mechanics). “Geometry, chronometry and hylometry are a-priori theories which make empirical measurements of space, time and materia ‘possible’. They have to be established before physics in the modern sense of an empirical science, with hypothetical fields of forces, can begin. Therefore, I should like to call these disciplines by a common name: protophysics.” Lorenzen, Normative Logic and Ethics, p. 60.

⁶³On the fundamental nature of epistemological dualism see also Mises, Theory and History, pp. 1–2.

⁶⁴On the aprioristic character of the category of causality see Mises, Human Action, chapter 1; Hoppe, Kritik der kausalwissenschaftlichen Sozialforschung; idem, “Is Research Based on Causal Scientic Principles Possible in the Social Sciences?”; on the causality principle as a necessary presupposition in particular also of the indeterminacy principle of quantum physics and the fundamental misconception involved in interpreting the Heisenberg-principle as invalidating the causality principle see Kambartel, Erfahrung und Struktur, pp. 138–40; also Hoppe, “In Defense of Extreme Rationalism,” footnote 36. In fact, it is precisely the indisputable praxeological fact that separate measurement acts can only be performed sequentially which explains the very possibility of irreducibly probabilistic-rather than deterministic-predictions as they are characteristic of quantum physics; and yet, in order to perform any experiments in the field of quantum mechanics, and in particular to repeat two or more experiments and state this to be the case, the validity of the causality principle must evidently already be presupposed.

⁶⁵On the necessary complementarity of the categories of causality and teleology see Mises, Human Action, p. 25; idem, The Ultimate Foundation of Economic Science, pp. 6–8; Hoppe, Kritik der kausalwissenschaftlichen Sozialforschung; idem, “Is Research Based on Causal Scientific Principles Possible in the Social Sciences?”; also G. v. Wright, Norm and Action (London: Routledge and Kegan Paul, 1963); idem, Explanation and Understanding (Ithaca, N.Y.: Cornell University Press, 1971); K. O. Apel, Die Erklären: Verstehen Kontroverse in transzendental-pragmatischer Sicht (Frankfurt/M.: Suhrkamp, 1979).

⁶⁶More precisely still: it is structured according to the categories of logic, arithmetic, and protophysics (including geometry). See note 62 above.

⁶⁷On the logic of history and sociology as reconstructive disciplines see in addition to the works of Mises mentioned at the outset of this chapter Hoppe, Kritik der kausalwissenschaftlichen Sozialforschung, chapter 2.

⁶⁸On the categorical distinctiveness of praxeological theory and history and sociology and the logical constraints that praxeology imposes on historical and sociological research as well as on social and economic predictions see Mises, Human Action, pp. 51–59, 117–18; Hoppe, “In Defense of Extreme Rationalism.“