Leo Schönfeld-Illy, Das Gesetz des Grenznutzens (1948)

Leo Schönfeld-Illy’s Das Gesetz des Grenznutzens is a single-author theoretical monograph on marginal utility and the consumer’s economic calculation. Its central concern is not to restate marginal utility as a psychological law of satisfaction, but to clarify how an “unrechenbarer Nutzen” can nevertheless enter monetary calculation. The book’s thesis is that the marginal-utility law has its genuine economic meaning only when understood as a principle of consumer budgeting, valuation, and demand-price formation.

Darum besteht die besondere Schwierigkeit der Wirtschaftsrechnung des Konsumenten, die auch ihre gesonderte Behandlung in der ökonomischen Theorie erfordert, darin: den unrechenbaren Nutzen in begründeter, zweckerfüllender Art in die Geldrechnung zu bringen.

English translation: Hence the peculiar difficulty of the consumer’s economic calculation—which also requires its separate treatment in economic theory—consists in this: to bring the incalculable utility, in a well-grounded and purpose-serving manner, into monetary calculation.

This formulation defines the scope of the inquiry. The consumer’s problem is not merely choosing among pleasures, but making defensible monetary dispositions in the face of useful things whose utility is not itself arithmetically measurable. Schönfeld-Illy therefore separates the economic content of marginal utility from both hedonistic psychology and abstract functionalism. His reconstruction of Wieser is decisive: stripped of misleading accretions, the “value” meant by the marginal law is not an inner quantity of feeling, but the consumer’s demand price.

Wenn wir so vorgehen, alles weglassen, was weggelassen werden muß, und uns hinsichtlich des Realen, das dann bleibt, an Wiesers eigene Erklärung, an seine Worte und ihren Sinn halten, dann steht eindeutig fest: jener Wert, den Wieser mit seinem Grenzgesetz gemeint hat, ist der Nachfragepreis.

English translation: If we proceed in this way—omitting everything that must be omitted, and, as regards what is real and remains, holding to Wieser’s own explanation, to his words and their meaning—then it stands unambiguously established: the value which Wieser meant by his marginal law is the demand price.

The conceptual move is important because it translates marginal utility into the language of economic action. The margin is not a mystical point at which pleasure becomes measurable; it is the point at which a permissible money disposition is established. From there the decision can be carried over to the relevant stock of goods without calculating each unit’s separate utility. Marginal utility is thus a rule of economical simplification and justification.

Die ökonomische Relevanz des Grenznutzens ermöglicht die begründete Übertragung einer an der Grenze einer Gutsmenge als wirtschaftlich zulässig befundenen Verfügung auf diese gesamte Gutsmenge ohne Veranschlagung des Nutzens ihrer übrigen Teilmengen.

English translation: The economic relevance of marginal utility makes it possible, on well-founded grounds, to extend a disposition found economically admissible at the margin of a quantity of goods to the entire quantity of those goods, without appraising the utility of its remaining sub-quantities.

The later constructive chapters extend this argument into a critique of static equilibrium theory. Schönfeld-Illy resists the Walrasian and Paretian image of an all-embracing calculator that solves price and demand simultaneously from outside the economy. In such a static system, the real sequence of action disappears and the circularity of determination is merely concealed.

Die Preise werden durch die Nachfrage determiniert, die Nachfrage wird durch die Preise determiniert!

English translation: Prices are determined by demand; demand is determined by prices!

Against this circle, the book insists on the primacy of actual calculation by economic subjects. Prices and demands are not determined by a universal formula but through plans, expectations, and revisions made by persons who must calculate before all relevant facts are known. This is why the consumer’s calculation deserves separate theoretical treatment: it is the site where subjective wants, objective prices, money budgets, and anticipated circumstances meet.

Es gilt also: wer wirtschaftet, der rechnet selbst.

English translation: The rule therefore holds: whoever manages an economy calculates for himself.

The work’s dynamic alternative is therefore a theory of planned calculation under expected conditions. Economic action is forward-looking: the consumer does not calculate with a completed world of data, but with anticipated prices, needs, quantities, and opportunities. Schönfeld-Illy names this the principle of expected data in economic calculation.

Wir haben somit in der planenden Wirtschaftsrechnung ein Prinzip der erwarteten Größen und Umstände vor uns; mathematisch bezeichnet: das Prinzip der erwarteten Daten in der Wirtschaftsrechnung.

English translation: We thus have before us, in planning economic calculation, a principle of the expected magnitudes and circumstances; mathematically expressed: the principle of the expected data in economic calculation.

The relevance of the book lies in this redirection of marginal utility theory. It preserves the Austrian concern with subjective value while refusing to treat value as a directly measurable psychic magnitude. It also criticizes mathematical equilibrium theory not simply for using mathematics, but for losing the economic meaning of calculation when it substitutes an external “Universalrechner” for the actor’s own reckoning. Marginal utility, in Schönfeld-Illy’s account, is the law that permits the consumer to convert qualitative wants into monetary choices at the margin, thereby making demand-price formation intelligible as a real process of planning rather than a timeless equation.