Ignorance of the fact excuses; ignorance of the law excuses not. Every man must be taken to be cognizant of the law; otherwise there is no saying to what extent the excuse of ignorance may not be carried.

Explanation

(English-origin maxim.) Ignorance of fact may excuse a party from liability, but ignorance of law never does — every person is conclusively presumed to know the law, and no claim of unfamiliarity will serve as a defense.

Where this applies

• A man unknowingly buys stolen goods at a flea market and is excused from criminal liability because he was genuinely ignorant of the fact that the goods were stolen.
• A taxpayer fails to file a return, claiming he did not know it was required by law; the court rejects the defense because ignorance of the tax code is no excuse.
• A pharmacist sells a controlled substance without a prescription, believing the law had changed; the court convicts him because ignorance of the law — unlike ignorance of fact — provides no defense.