Tokumaru first notes that, with respect to the natural sciences, Mises endorses what Popper called “naïve inductivism” with undefended assumptions of the uniformity of nature; that Mises also holds that social regularities are qualitatively different from regularity in the natural sciences; and that Mises contends that social sciences use an a priori method (Tokumaru 2009: 164).
Mises’s idea is that, because human beings are endowed with a priori mental “categories” that make ordered experience of the world possible (and have been shaped biologically by reality), therefore the theorems of praxeology, derived by deduction, are also a priori valid.
But, as Tokumaru notes, Mises conflates two different senses of the a priori as noted by Popper: (1) the “psychological a priori” and (2) “a priori validity.”
The notion of the “psychological a priori” denotes certain human psychological propensities, given to us by biology and evolution, which allow us to interpret the world in an apparent a priori manner, but which nevertheless are not logically a priori at all, and may be mistaken or ultimately wrong (Tokumaru 2009: 165). The concept of “a priori validity” refers to the strict epistemological notion of necessary truth, but one cannot obtain “a priori validity” merely from notions that are merely “psychologically a priori,” such as Mises’s categories (Tokumaru 2009: 165).
Tokumaru then argues that there are four ways in which Mises might interpret the epistemological status of the action axiom, as follows:
(1) an observational statement or one describing experiences from introspection;Tokumaru argues rightly that options (1) and (2) require synthetic a priori knowledge (Tokumaru 2009: 166), which is untenable, just as many people, including Popper (2009) have shown. Ultimately, (1) and (2) do require that the action axiom is synthetic a posteriori, and also that praxeology and all its theories are in the same status.
(2) a proposition “about the basic ontological form of the social universe, describing its essential characteristics”;
(3) a mere tautological definition, which is adopted by convention, and
(4) a methodological principle as demanded by the method of “methodological individualism.” (Tokumaru 2009: 165).
If Mises adopts option (3), this implies that the action axiom is analytic a priori, and thus a vacuous tautology, telling us nothing necessary about the world. It would follow from this that all of praxeology is also vacuous and non-informative, and says nothing of the world.
Finally, option (4) implies that the action axiom is a mere “methodological principle,” but such a principle still needs epistemological justification (which simply returns us to the three options above), unless the principle is construed as a mere pragmatic one that is not defended as either true or false. In the latter case, the theories of praxeology also lose their status as synthetic a priori, and the whole system cannot provide certain knowledge.
Popper, Karl R. 2009. The Two Fundamental Problems of the Theory of Knowledge (trans. Andreas Pickle). Routledge, London and New York.
Tokumaru, N. 2009. “Popper’s Analysis of the Problems of Induction and Demarcation and Mises’ Justification of the Theoretical Social Sciences,” in Z. Parusnikova and R. S. Cohen (eds.), Rethinking Popper. Springer, Dordrecht and London.