action (those inherent in the logic of the means-end structure as such) that can be grasped by a priori reasoning, corresponds to Frege’s third realm. And Frege’s campaign against psychologism – the error of reducing logical relations to psychological ones, the third realm to the inner realm – is matched my Mises’ insistence on the distinction between thymology and praxeology, and his condemnation of “psychologistic epistemology, which ascribed an empirical character even to the laws of thought.”5
2.The Helpful Frege
Frege’s account of the three realms lends valuable assistance to the Misesian project in a number of ways. For example, Frege’s distinction between the privateness of the inner realm and the publicness of the third realm shows how a defender of Misesian apriorism can reply to a well-known criticism from Milton Friedman:
That methodological approach, I think, has very negative influences. ... [It] tends to make people intolerant. If you and I are both praxeologists, and we disagree about whether some proposition or statement is correct, how do we resolve that disagreement? We can yell, we can argue, we can try to find a logical flaw in one another’s thing, but in the end we have no way to resolve it except by fighting, by saying you’re wrong and I’m right.6
Friedman is clearly thinking of the difference between empirical and a priori investigations as turning on the presence or absence of publicly accessible modes of resolving disputes; he evidently thinks of a priori knowledge as a matter of turning to some private, incommunicable source of intuition uncheckable by anyone else – in short, as an inner-realm item, a “presentation” in Frege’s sense. But praxeology, like logic or mathematics, deals not with Fregean presentations but with Fregean thoughts, which are at least as publicly accessible as empirical,
5 Ludwig von Mises, Epistemological Problems of Economics, trans. George Resiman (New York University Press, 1976), p. 22.
6 Quoted in Alan Ebenstein, Friedrich Hayek: A Biography (New York: Palgrave, 2001), p. 273.
R. T. Long – Wittgenstein, Praxeology, and Frege’s Three Realms – p. 4