Frank Knight

Frank Knight (1885–1972) was an American economist whose 1921 book Risk, Uncertainty, and Profit introduced the foundational distinction between risk — situations where probabilities are known and outcomes can be enumerated — and uncertainty — situations where probabilities are unknown and the set of outcomes is not well-defined. This distinction, now called Knightian uncertainty, was largely ignored by the economics profession, which preferred to treat all uncertainty as if it were risk amenable to probabilistic analysis. Knight argued that profit arises precisely from uncertainty: in a world of pure risk, competition would eliminate all profit, and only uncertainty — the inability to assign probabilities to future outcomes — creates the entrepreneurial opportunity for profit. His work thus anticipated the critique of decision theory and game theory that John Maynard Keynes would later develop: that formal models which assume well-defined probability distributions are structurally inadequate for systems in which agents must act without knowing what they do not know. Knight's concept of uncertainty is not a temporary state of ignorance but a permanent feature of economic systems whose future depends on the decisions of agents who are themselves uncertain. The modern reduction of Knightian uncertainty to ambiguity or model