For a brief moment starting in the 1870s, economics was close to becoming a genuine science of human action. Carl Menger in Vienna, William Stanley Jevons in England, and Léon Walras in Lausanne independently (re)discovered what the Spanish Scholastics had only glimpsed centuries earlier: Value is not inherent in objects, forged in the sweat of labor or dictated by cost; value is subjective, existing and emerging in the minds of acting individuals confronting scarcity—individuals who choose, at the margin, between scarce means and infinite wants. What began as a breakthrough in understanding