thought and which someone has about these things.10
If one fails to distinguish between mental acts (“presentations,” inner-realm items) on the one hand from their contents (“components of a thought,” third-realm items) and on the other from their objects (“the things themselves,” outer-realm items), one may fall into the error of supposing that any presentation of a cat that fails to include its colour or posture must thereby have as its object or content a colourless, postureless cat. That is the mistake that Frege is diagnosing in the above passage, and Friedman’s is like unto it: he seems to assume that if an economic account fails to include a presentation of the wheat-trader’s eye-colour or ancestry, it must have as its object or content an eye-colour-less, ancestry-less wheat-trader – and so must be “unrealistic.” But once we follow Frege in distinguishing among the three realms, Friedman’s psychologistic assumption dissolves.11
3.The Unhelpful Frege
But there are other areas where it is less clear that Frege’s distinctions lend Mises’ project much support. For example, just how helpful is Frege’s critique of psychologism to Mises’ critique of polylogism? It depends whether one has in mind normative polylogism (the view that there are multiple, mutually incompatible, but equally valid logics) or descriptive polylogism (the view that different individuals or groups think in accordance with the rules of different logics, whether or not these logics are to be regarded as equally valid). When it comes to normative polylogism, Frege’s critique of psychologism is definitely relevant, since for Frege the principal error of psychologism is that in treating logical laws as merely laws of psychology, laws descriptive of how minds like
10 Frege, Review of Husserl, op. cit., pp. 324-5.
11 For more on the distinction between specifying the absence of a feature and failing to specify its presence, see Roderick T. Long, “Realism and Abstraction in Economics: Aristotle and Mises versus Friedman,” Quarterly Journal of Austrian Economics 9, no. 3 (Fall 2006), pp. 3-23, as well as Long, “The Benefits and Hazards of Dialectical Libertarianism,” Journal of Ayn Rand Studies 2, no. 2 (Spring 2001), pp. 395-448, and Long, “R. G. Collingwood: Historicist or Praxeologist?” (unpublished working paper).
R. T. Long – Wittgenstein, Praxeology, and Frege’s Three Realms – p. 7