During the first few decades of the twentieth century, legal theory on both sides of the Atlantic was characterized by a tremendous amount of skepticism toward the private law concepts of property and contract. In the United States and France, Oliver Wendell Holmes and François Gény led the charge with withering critiques of the abuse of deduction, exposing their forebears’ supposedly gapless system of private law rules for what it was, a house of cards built on the ideological foundations of laissez faire capitalism. The goal was to make the United States Constitution and the French civil code more responsive to the realities of industrialization. Unlike the other participants in this transatlantic critique, François Gény simultaneously insisted on the immutability of justice and social utility. His “ineluctable minimum of natural law” would guide judges and jurists toward the proper social ends, replacing deduction with teleology. The problem was that nearly all of Gény's contemporaries were perplexed by his conception of natural law, which lacked the substance of the natural rights tradition of the eighteenth and nineteenth centuries and the historicist impulse of the early twentieth. No one was more perplexed than Oliver Wendell Holmes, whose more thoroughgoing skepticism led him to see judicial restraint as the only solution to the abuse of deduction. The ultimate framework for this debate was World War I, in which both Holmes and Gény thought they had found vindication for their views. Events on the battlefield reaffirmed Gény's commitment to justice just as they reignited Holmes’ existential embrace of the unknown. In a sense, the limits of their skepticism would be forged in the trenches of the Great War.