uncertain

Uncertain is an adjective describing a state in which something is not known or not definite. It can refer to doubt about facts, outcomes, or values; situations that are ambiguous or open to multiple interpretations; or events that may or may not occur. In everyday language, uncertainty appears in weather forecasts, economic outlooks, and personal decisions.

Etymology traces uncertain to Latin incertus, meaning not fixed or settled, and it passed into Old French as incertain before entering English with the current form and sense.

In probability and statistics, uncertainty denotes a lack of exact knowledge about a quantity of interest. It is commonly represented by probability distributions, error bars, or confidence intervals. Analysts distinguish epistemic uncertainty, from incomplete knowledge that could be reduced with more information, from aleatoric uncertainty, due to inherent randomness. Uncertainty quantification analyzes and propagates these sources through models to yield robust conclusions.

In philosophy, uncertainty concerns the scope and justification of knowledge, often tied to skepticism and the criteria for belief. In science and decision making, strategies aim to manage uncertainty through data collection, sensitivity analysis, scenario planning, and risk assessment. In physics, the Heisenberg uncertainty principle states that certain pairs of physical properties cannot be simultaneously measured with arbitrary precision; this expresses a fundamental limit rather than a mere lack of information. Overall, uncertainty is a central concept across disciplines, reflecting both limits of knowledge and the variability inherent in many systems.