Indian Criminal Law | Updated 28 October 2026
IPC Section 79 and BNS Section 17: Act Justified by Law or Good-Faith Mistake of Fact
A person may be protected from criminal liability when an act is justified by law, or when the person, because of a mistake of fact and acting in good faith, believes the law justifies the act. A mistake about what the law permits is different and does not itself attract this exception.
Section 79 IPC: Text of the provision
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.
This is a general exception to criminal liability, not an independent offence or a punishment provision. The exception is concerned with lawful justification and a genuine, good-faith factual misunderstanding.
Statutory illustration explained
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.
In this illustration, A reasonably interprets the visible circumstances as a murder and apprehends Z to take Z before the authorities. Although the facts later reveal that Z acted in self-defence, the illustration protects A because the action was based on a good-faith mistake of fact and the applicable legal power. It does not authorise arbitrary detention or excessive force.
BNS Section 17: Corresponding law
Section 17 of the Bharatiya Nyaya Sanhita, 2023 is titled Act done by a person justified, or by mistake of fact believing himself justified, by law. It preserves the central distinction between a mistake of fact and a mistake of law, and the requirement of good faith.
Consult the official BNS Act text on India Code for the enacted wording and illustrations.
Essential conditions for the exception
- Actual legal justification: The law authorises the conduct; or
- Good-faith factual belief: A factual error leads the person genuinely to believe the conduct is legally justified.
- Not a mistake of law: A mistaken understanding of the legal rule itself is not covered by this ground.
- Due care and attention: Good faith under the criminal code requires appropriate care and attention in the circumstances; an unsupported assumption may not suffice.
- Connection to the act: The claimed legal authority and factual belief must relate to the particular conduct in question.
Mistake of fact compared with mistake of law
| Question | Mistake of fact | Mistake of law |
|---|---|---|
| What is misunderstood? | A real-world circumstance, identity or event | The content or scope of the legal rule |
| Example | A person reasonably believes an observed act is a murder, but it was lawful self-defence | A person believes the law permits arrest without any applicable legal authority |
| Section 79 / Section 17 | May protect conduct if all conditions are met | Does not provide this exception merely because the law was misunderstood |
How Section 79 differs from related exceptions
IPC Section 76 / BNS Section 14 concerns acts a person is bound by law to do, or in good faith believes they are bound to do because of a factual mistake. IPC Section 79 / BNS Section 17 concerns acts the person is justified by law in doing, or in good faith believes are justified because of a factual mistake. A legal duty and a legal permission are not the same thing.
IPC Section 77 / BNS Section 15 addresses judges acting judicially, while IPC Section 78 / BNS Section 16 addresses acts pursuant to court judgments or orders.
Practical application and limits
Whether the exception applies depends on the surrounding facts, the legal authority invoked, the person's belief, and the care exercised. It is not enough simply to assert good intentions. The court assesses the circumstances and the applicable rules on general exceptions and evidence.
For instance, a person who intervenes on an honestly and carefully assessed factual belief that a serious offence is occurring may invoke the exception if the law authorises the intervention. A person who knows the facts but incorrectly assumes that the law permits the same conduct cannot rely on a mistake of law under this provision.
Frequently asked questions
What is the BNS equivalent of IPC Section 79?
Section 17 of the Bharatiya Nyaya Sanhita, 2023.
Is every mistake of fact a defence?
No. The statutory conditions must be satisfied, including good faith and a belief that the act was legally justified.
Does ignorance of the law qualify?
No. Section 79 IPC and Section 17 BNS expressly distinguish mistakes of fact from mistakes of law.
Can a private person arrest anyone they suspect?
No. Any power to apprehend a person is governed by the applicable procedural law and its conditions. The statutory illustration is not an unrestricted arrest power.
Does the IPC still apply to older incidents?
It may apply to conduct predating 1 July 2024, subject to repeal, savings and the relevant facts.
Official legislation and further reading
- India Code: Bharatiya Nyaya Sanhita, 2023 (Act 45 of 2023)
- India Code: Central Acts and historical legislation
- Indian Penal Code: Sections and punishments
This article is general legal information. Application of a general exception depends on the applicable law, evidence and circumstances.