Onus Probandi

A Latin legal phrase meaning 'the burden of proving,' rooted in ancient Roman law. The full maxim — onus probandi incumbit ei qui dicit, non ei qui negat ('the burden of proof lies upon him who affirms, not him who denies') — codified the logical principle that one cannot be required to prove a negative. It entered English legal usage by the late 16th century and remains foundational in both common law and civil law traditions.