Knightian uncertainty

Knightian uncertainty is the distinction between measurable risk and unmeasurable uncertainty — situations where probability distributions are not merely unknown but unknowable. Frank Knight introduced the term in Risk, Uncertainty, and Profit (1921) to explain entrepreneurial profit as the return to bearing genuine uncertainty.

Modern economics suppressed this distinction, treating all uncertainty as quantifiable risk. This suppression underlies the financial models that failed in 2008 and the climate models that produce precise confidence intervals for inherently uncertain parameters. Knightian uncertainty is distinct from epistemic uncertainty, which operates within a known model, and closely related to ontological uncertainty — uncertainty about what the possibilities even are. It can only be managed through optionality: preserving choices that remain valuable across unknown futures.