Three Men Who Solved the Diamond-Water Paradox in the Same Year
In 1871, three economists independently solved why water costs less than diamonds — and none knew the others were working on it.
Adam Smith called it the paradox of value: water, essential for life, is nearly free. Diamonds, decorative rocks, command enormous prices. Classical economics had no satisfying answer. Smith's own labor theory of value didn't help much — water requires labor to transport but remains cheap.
In 1871, three economists on separate continents published books that each contained the same solution. William Stanley Jevons in Manchester published The Theory of Political Economy. Carl Menger in Vienna published Grundsätze der Volkswirtschaftslehre (Principles of Economics). Léon Walras in Lausanne published Éléments d'économie politique pure. None had read the others' work before finishing their own.
The answer was marginal utility. Value, they each argued, is not determined by a good's total usefulness but by the usefulness of the next unit consumed. You have abundant water. The next glass of water adds very little to your wellbeing. You have few diamonds. The next diamond adds a great deal of perceived value. Price tracks marginal utility, not aggregate utility.
This reasoning — now called the Marginal Revolution — demolished the labor theory of value that had underpinned both classical and early Marxist economics. Marx's Das Kapital (published in 1867) rested heavily on the labor theory. The marginal utility framework replaced it within a generation in academic economics.
The independent simultaneous discovery is one of the more striking coincidences in intellectual history. Historians of economics point to it as evidence that the time was ripe: enough mathematical sophistication existed, and the failures of classical theory had become obvious enough, that the insight was waiting to be found.
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