From Human Action — surrounding passage

It has given proof of its expediency. However, one must not overlook the fact that the manipulation of this singular and logically somewhat strange procedure requires caution and subtlety, and that uncritical and superficial minds have again and again been led astray by careless confusion of the two epistemologically different methods implied. There are no such things as a historical method of economics or a discipline of institutional economics.

“There is economics and there is economic history. The two must never be confused.”

All theorems of economics are necessarily valid in every instance in which all the assumptions presupposed are given. Of course, they have no practical significance in situations where these conditions are not established. The theorems referring to indirect exchange are not applicable to conditions where there is no indirect exchange. But this does not impair their validity.