Hans-Hennann Hoppealways understood it, now also becomes discernible. The prevailingempiricist-formalist orthodoxy conceives of arithmeticas <strong>the</strong> manipulation ofarbitrarily defined signs according toarbitrarily stipulated transformation rules, <strong>and</strong> thus as entirelyvoid of any empirical meaning. For this view; whichevidently makes arithmetic nothing but pIa); however skillfulit might be, <strong>the</strong> successful applicability of arithmetic inphysics is an intellectual embarrassment. Indeed, empiricistformalistswould have to explain away this fact as simplybeing a miraculous event. That it is no miracle, however,becomes apparent once <strong>the</strong> praxeological or-to use here <strong>the</strong>terminology of<strong>the</strong> most notable rationalist philosopher-ma<strong>the</strong>maticianPaul Lorenzen <strong>and</strong> his school-<strong>the</strong> operative or constructivistcharacter of arithmetic is understood. Arithmetic<strong>and</strong> its character as an a priori-syn<strong>the</strong>tic intellectual disciplineis rooted in our underst<strong>and</strong>ing of repetition, <strong>the</strong>repetition of action. More precisel); it rests on our underst<strong>and</strong>ing<strong>the</strong> meaning of"do this-<strong>and</strong> do this again, startingfrom <strong>the</strong> present result." And arithmetic <strong>the</strong>n deals withreal things: with constructed or constructively identifiedunits of something. It demonstrates what relations are tohold between such units because of <strong>the</strong> fact that <strong>the</strong>y areconstructed according to <strong>the</strong> rule of repetition. As PaulLorenzen has demonstrated in detail, not all of what presentlyposes as ma<strong>the</strong>matics can be constructivelyfounded-<strong>and</strong> those parts, <strong>the</strong>n, should ofcourse be recognizedfor what <strong>the</strong>y are: epistemologically worthless symbolicgames. But all of <strong>the</strong> ma<strong>the</strong>matical tools that are actuallyemployed in physics, i.e., <strong>the</strong> tools ofclassical analysis, can beconstructively derived. They are not empirically void symbolisms,but true propositions about reali~ They apply toeverything insofar as it consists of one or more distinctunits, <strong>and</strong> insofar as <strong>the</strong>se units are constructed or identifiedThe Ludwig von Mises Institute • 73
<strong>Economic</strong> <strong>Science</strong> <strong>and</strong> <strong>the</strong> <strong>Austrian</strong> <strong>Method</strong>as units by a procedure of"do it again, construct or identifyano<strong>the</strong>r unit by repeating <strong>the</strong> previous operation."S9 Again,one can say, of course, that 2 plus 2 is sometimes 4 butsometimes 2 or 5 units, <strong>and</strong> in observational reality; for lionsplus lambs or for rabbits, this may even be true,60 but in <strong>the</strong>reality of action, in identifying or constructing those unitsin repetitive operations, <strong>the</strong> truth that 2 plus 2 is neveranything but 4 could not possibly be undone.Fur<strong>the</strong>r, <strong>the</strong> old rationalist claims that geometry; that is,Euclidean geometry is a priori <strong>and</strong> yet incorporates empiricalknowledge about space becomes supported, too, in viewof our insight into <strong>the</strong> praxeological constraints on knowledge.Since <strong>the</strong> discovery of non-Euclidean geometries <strong>and</strong>590n a rationalist interpretation of arithmetic see Blanshard, Rcason <strong>and</strong>Analysis~ pp. 427-31; on <strong>the</strong> constructivist foundation ofarithmetic, in particular,see Lorenzen, EinfUhrung in die operative Logik und Ma<strong>the</strong>matik; idem, <strong>Method</strong>ischesDenken, chapters 6, 7; idem, Normative Logic <strong>and</strong> Ethics~ chapter 4; on <strong>the</strong>constructivist foundation of classical analysis see P. Lorenzen, Differential undIntegral: Eine konstruktive EinfUhrung in die klassische Analysis (Frankfurt/M.:Akademische Verlagsgesellschaft, 1965); for a brilliant general critique ofma<strong>the</strong>matical formalism see Kambartel, Erfahrung und Struktur, chapter 6,esp. pp. 236-42; on <strong>the</strong> irrelevance of<strong>the</strong> famous Godel-<strong>the</strong>orem for a constructivelyfounded arithmetic see P. Lorenzen,Metama<strong>the</strong>matik (Mannheim: BibliographischesInstitut, 1962); also Ch. Thiel, "Das Begrlindungsproblem derMa<strong>the</strong>matik und die Philosophie," in E Kambartel <strong>and</strong> J. Mittelstrass, eds.,Zum normativen Fundament der Wissenschaft, esp. pp. 99-101. K. Godel'sproof-which, as a proof, incidentally supports ra<strong>the</strong>r than undermines <strong>the</strong>rationalist claim of<strong>the</strong> possibility ofapriori knowledge-only demonstrates that<strong>the</strong> early formalist Hilbert program cannot be successfully carried through,because in order to demonstrate <strong>the</strong> consistency of certain axiomatic <strong>the</strong>oriesone must have a meta<strong>the</strong>ory with even stronger means than those formalizedin <strong>the</strong> object-<strong>the</strong>ory itself. Interestingly enough, <strong>the</strong> difficulties of<strong>the</strong> formalistprogram had led <strong>the</strong> old Hilbert already several years before Godel's proof of1931 to recognize <strong>the</strong> necessity ofreintroducing a substantive interpretation ofma<strong>the</strong>matics ala Kant, which would give its axioms a foundation <strong>and</strong> justificationthat was entirely independent of any formal consistency proofs. SeeKambartel, Erfahrung und Struktu1j pp. 185-87.60Examples of this kind are used by Karl Popper in order to "refute" <strong>the</strong>rationalist idea of rules of arithmetic being laws of reality. See Karl Popper,Conjectures <strong>and</strong> Refutations (London: Routledge <strong>and</strong> Kegan Paul, 1969), p. 211.74 • The Ludwig von Mises Institute