outer-realm items; after all, mathematicians have no problem checking one another’s work. By Frege’s standards, Friedman is confusing the third realm with the inner realm, thoughts with presentations, the logical with the psychological:
[N]o-one has someone else’s presentation but only his own, and no-one knows how far his presentation – e.g. that of red – agrees with that of someone else .... With thoughts, it is quite different: one and the same thought can be grasped by many people.7
Or, as Collingwood puts the point:
We understand what Newton thought by thinking – not copies of his thoughts – a silly and meaningless phrase – but his thoughts themselves over again. ... A person who failed to understand that thoughts are not private property might say that it is not Newton’s thought that I understand, but only my own. That would be silly because, whatever subjective idealism may pretend, thought is always and everywhere de jure common property, and is de facto common property wherever people at large have the intelligence to think in common.8
Frege’s distinction among the three realms also offers the Austrian a way of replying to another of Friedman’s criticisms; in response to Austrian objections to the use of unrealistic assumptions in economics, Friedman replies that such assumptions are unavoidable:
A theory or its “assumptions” cannot possibly be thoroughly “realistic” in the immediate descriptive sense so often assigned to this term. A completely “realistic” theory of the wheat market would have to include not only the conditions directly underlying the supply and demand for wheat but also the kind of coins or credit instruments used to make exchanges; the personal characteristics of wheat-traders such as the color of each trader’s hair and eyes, his antecedents and education, the number of members of his family, their characteristics, antecedents, education, etc.; the kind of soil on which the
7 Frege, Review of Dr. E. Husserl’s Philosophy of Arithmetic, trans. E. W. Kluge, p. 325; in Mind, New Series 81, no. 323 (July 1972), pp. 321-337.
8 R. G. Collingwood, The Idea of History, Revised Edition: With Lectures 1926-1928, ed. Jan van der Dussen (Oxford University Press, 1994), p. 450.
R. T. Long – Wittgenstein, Praxeology, and Frege’s Three Realms – p. 5