Ignorantia facti excusat
Latin: Ignorance of fact excuses.
Also called: Mistake of fact, Ignorantia facti excusat, ignorantia juris non excusat
A person who acts under an honest mistake about facts, in good faith, may be excused, unlike a person who is ignorant of the law.
Explained
Ignorantia facti excusat means ignorance of fact excuses. It is usually quoted with its counterpart, ignorantia juris non excusat, ignorance of law does not excuse. A person who acts under a mistaken belief about facts, which if true would make his act lawful, is not treated as having the guilty mind the law requires.
In criminal law the maxim is codified in two general exceptions of the BNS. Under Section 14, nothing is an offence which is done by a person who, by reason of a mistake of fact and not of law, in good faith believes himself bound by law to do it. Under Section 17, nothing is an offence which is done by a person who, by reason of a mistake of fact and not of law, in good faith believes himself justified by law in doing it. These were earlier Sections 76 and 79 of the IPC. The elements are a mistake of fact, not of law; a belief held in good faith, which under Section 2(11) of the BNS means with due care and attention; and a belief that, if true, would make the act lawful.
Good faith is the limit. A careless belief does not protect, and the accused bears the burden of proving the exception under Section 108 of the BSA. The defence also does not usually help in offences of strict liability, where the statute does not require a guilty mind.
Contract law applies the same contrast. Under Section 20 of the Contract Act, an agreement is void where both parties are under a mistake as to a matter of fact essential to it. Under Section 21, a contract is not voidable because of a mistake as to any law in force in India, though a mistake about foreign law is treated as a mistake of fact.
What the law says
Nothing is an offence which is done by a person who is, or who by reason of a mistake of fact and not by reason of a mistake of law in good faith believes himself to be, bound by law to do it.
Illustrations.
(a) A, a soldier, fires on a mob by the order of his superior officer, in conformity with the commands of the law. A has committed no offence.
Mistake of fact: person believing himself bound by law
Earlier law: IPC 76. Act done by a person bound, or by mistake of fact believing himself bound, by law.
Nothing is an offence which is done by any person who is justified by law, or who by reason of a mistake of fact and not by reason of a mistake of law in good faith, believes himself to be justified by law, in doing it.
Illustration.
A sees Z commit what appears to A to be a murder. A, in the exercise, to the best of his judgment exerted in good faith, of the power which the law gives to all persons of apprehending murderers in the fact, seizes Z, in order to bring Z before the proper authorities. A has committed no offence, though it may turn out that Z was acting in self-defence.
Mistake of fact: person believing himself justified by law
Earlier law: IPC 79. Act done by a person justified, or by mistake of fact believing himself, justified, by law.
Where both the parties to an agreement are under a mistake as to a matter of fact essential to the agreement, the agreement is void.
Explanation.—An erroneous opinion as to the value of the thing which forms the subject-matter of the agreement, is not to be deemed a mistake as to a matter of fact.
Illustrations
Agreement void where both parties are mistaken as to fact
A contract is not voidable because it was caused by a mistake as to any law in force in [India]; but a mistake as to a law not in force in [India] has the same effect as a mistake of fact.
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Illustration
Mistake of law in force in India does not make contract voidable
Earlier law: Section 76, IPC, Section 79, IPC
Example
Illustration (b) to Section 14 of the BNS: an officer of a Court, ordered to arrest Y, arrests Z after due enquiry, believing Z to be Y. He has committed no offence.
For the exam
- Meaning: ignorance of fact excuses; ignorance of law does not.
- Codified in BNS Sections 14 and 17, earlier IPC Sections 76 and 79.
- The mistake must be of fact, in good faith, and such that the act would be lawful if the facts were true.
- Section 20 ICA: bilateral mistake of essential fact makes the agreement void.
- Section 21 ICA: mistake of Indian law does not make a contract voidable.
33 questions in the Law Maker question bank use this maxim. Practise Legal Maxims & Jurisprudence questions
Related terms
- Ignorantia juris non excusatIgnorance of the law is no excuse. A person cannot escape liability by claiming he did not know the law, though a mistake of fact made in good faith may excuse.
- Good faithUnder Section 2(11) of the BNS, nothing is done or believed in good faith if it is done or believed without due care and attention. Civil laws accept honesty alone.
- Mens reaThe mental element of a crime, such as intention, knowledge, dishonesty or rashness, which together with the physical act (actus reus) ordinarily constitutes an offence.
- Actus non facit reum nisi mens sit reaThe act alone does not make a person guilty; criminal liability ordinarily requires a guilty act (actus reus) accompanied by a guilty mind (mens rea).
- Bona fideIn good faith; genuine and honest, without fraud or deceit. Its opposite is mala fide. Statutes give good faith their own definitions.
Further reading
Checked 6 November 2026. Statutory text is quoted from the Bare Acts library, taken from India Code. See the full glossary.