Section 79 of the Indian Penal Code provides that nothing is an offence which is done by any person who is justified by law, or who by reason of mistake of fact and not by reason of mistake of law, in good faith, believes himself to be justified by law, in doing it.
Under this section, although an act may not be justified by law, yet if it is done under a mistake of fact, in the belief in good faith that it is justified by law it will not be an offence. Such cases are not uncommon where the Courts in the facts and circumstances of the particular case have exonerated the accused under s. 79 on the ground of his having acted in good faith under the belief, owing to a mistake of fact that he was justified in doing the act which constituted an offence.
As laid down in s. 52 of the Indian Penal Code, nothing is said to be done or believed in good faith which is done or believed without due care and attention.
The question of good faith must be considered with reference to the position of the accused and the circumstances under which he acted.
‘Good faith’ requires not logical infallibility but due care and attention. The question of good faith is always a question of fact to be determined in accordance with the proved facts and circumstances of each case.
Mistake of Fact
In the classical work Russel on Crime, vol. 1, p. 76, the concept of mistake of fact is tersely stated thus:
“When a person is ignorant of the existence of relevant facts, or mistaken as to them, his conduct may produce harmful results which he neither intended nor foresaw.”
At p. 79, the law is stated in these words:
“Mistake can be admitted as a defence provided
(1) that the state of things believed to exist would, if true, have justified the act done, and
(2) the mistake must be reasonable, and
(3) that the mistake relates to fact and not to law.”
In State Of Orissa vs Bhagaban Barik, the court said that,
“It may be laid down as a general rule that an alleged offender is deemed to have acted under that state of things which he in good faith and on reasonable grounds believed to exist when he did the act alleged to be an offence.”
Cases on Mistake of Fact
Emperor v. Jagmohan Thukral & Anr., AIR 1947 All. 99
In this case, the accused while travelling from Saharanpur to Dehradun near the Mohand pass picked up the loaded gun when he saw the eyes of an animal and fired at it which unfortunately hit two military officers. There was nothing to show that the accused knew that there was a military camp or that any military exercise was going on.
The question was whether the accused was liable for having committed an offence punishable under s. 307 of the Indian Penal Code.
The Court held that the accused was protected by s. 79 observing.
Dhara Singh v. Emperor, AIR 1947 Lahore 249
In this case, it was held that the accused was labouring under a mistake of fact with regard to the identity of the persons who had surrounded his house followed by an exchange of fire, thinking them to be his adversaries and by reason of that mistake of fact, Explanation I to s. 99 gave to him a right of private defence.
Chirangi v. State, AIR (1952) Nag. 282
In this case, where an accused under a moment of delusion, considered that his own son, to whom he was attached, was a tiger and he accordingly assaulted him with an axe, thinking by reason of mistake of fact that he was justified in destroying the deceased whom he did not regard to be a human being but a dangerous animal.
It was held that the accused was protected under s. 79 of the Indian Penal Code.
State Of Orissa vs Bhagaban Barik, 1987 AIR 1265, 1987 SCR (2) 785
 1987 AIR 1265, 1987 SCR (2) 785