Marx Has Not Proved His Fundamental Proposition That Labour Alone Governs Exchange Relations Either Objectively Or Subjectively

Thirdly—and this concerns the criticism of Marx in particular—I must ask with all plainness that if any use is made of the objective method it should be the right use. If external objective connections are shown to exist, which, like fate, control action with or without the knowledge, with or without the will of the doer, let them be shown to exist in their correctness. And Marx has not done this. He has not proved his fundamental proposition that labour alone governs exchange relations either objectively, from the external, tangible, objective world of facts, with which on the contrary they are in opposition, or subjectively, from the motives of the exchanging parties ; but he gives it to the world in the form of an abortive dialectic, more arbitrary and untrue to facts than has probably ever before been known in the history of our science.

--Eugen von Böhm-Bawerk, Karl Marx and the Close of His System: A Criticism, trans. Alice M. Macdonald (London: T. Fisher Unwin, 1898), 216.