A challenge

Observing correlation (or lack of it) between two phenomena of purposeful behavior is impossible. Only on material phenomena can correlation be observed. Just try to prove me wrong!

Hicks wrong on doing without the law of diminishing marginal utility

Hicks is wrong when he despises the concept of "diminishing marginal utility". (1) I would agree with him if he would merely refer to the cardinal utility's interpretation, i.e. to think of the concept as referring to actual somehow mensurable magnitudes of utility. (To be sure, this cardinal interpretation is not even Marshall's.(2)) However, Hicks seems to entirely do without the concept instead of just removing the cardinal interpretation. If so, he is plainly wrong. He confounds the unsuitability of the name with that of the concept. If only we use such a name as, for instance, "the law of worse marginal value of perfectly homogeneous goods" and interpret it as Rothbard does (3), we have a concept absolutely necessary to deduce the demand law and, in general, to develop price theory.

(1) Hicks, John. Value and Capital. 1939. Pages 20-25.
(2) See Marshall, Alfred. Principles of Economics. 1890 -eighth edition, 1920-. Book III, chapter III, note 1.
(3) Rothbard, Murray. Man, Economy, and State. Pages 21-33 and especially 73-74.