Regula Est
Defined in 2 dictionaries — Cyclopedic (1922), Stimson (1881)
The Cyclopedic Law Dictionary
Walter A. Shumaker and George Foster Longsdorf; ed. James C. Cahill · 1922
JURIS QUIDEM IGNOrance of law does not excuse, but that ignorance of a fact may excuse a party from the legal consequences of his conduct. Dig. 22. 6. 9; Broom, Leg. Max. (3d London Ed.) 232. See Irving, Civ. Law (4th Ed.) 74.
Glossary of Technical Terms, Phrases, and Maxims of the Common Law
Frederic Jesup Stimson · 1881
etc. v. Ignorantia facti, etc.