Mental incapacity is a defense which is used in criminal proceedings; it is the situation when a person is of appreciating the nature of the crime and differentiating right from wrong behavior and in this scenario the person is not into his full conscious which make them not legally accountable for the commission of the crime. In this case it must be noted that just by stating a mental disorder cannot act as a complete defense for escaping from the liability of the crime. For using this defense in criminal prosecution the defendant has prove the defense of insanity by a “preponderance of the evidence”


If a person is made liable for a crime which he has not even committed than it will result into violation of the basic human rights of any such person, an insane person who is not mentally capable to figure out the fact that whether what he is doing is right or not, when he is not in a condition to differentiate between the right and wrong when he is not able to conclude that what will be the end consequence of his act or omission, any such situation of insanity or mental incapacity as the facts may be the person can use the defense of insanity and escape from such liability.


Section 84 of the Indian penal code explains the any act committed by a person of unsound mind; this section says as follows that nothing will be considered as an offence if it is done by a person who at the time of doing the act was by reason of unsoundness of mind, is incapable of knowing the nature of the act he is doing and does it against the law.

Section 84 has many implicit features in it, this section classify the situation of unsound mind into two broad categories the first one is the major category which includes medical requirement of mental illness and the other one is the minor category, this category includes loss of reasoning requirement. The former category or the major category simply means a situation where the person is suffering from any kind of mental illness during the commission of the act for which he is being tried and the later or the minor category means the situation where the person is in incapable in analyzing the following situations that are

  1. Incapable of knowing the nature of the act or
  2. Incapable of knowing his act is wrong o
  3. Incapable of knowing it is contrary to law.

Both major (mental illness) and minor (loss of reasoning) criteria constitute legal insanity or mental incapacity and can be used as a valid defense in criminal prosecutions.

Section 84 Indian penal code, clearly embodies a fundamental maxim of criminal jurisprudence that is,

(a) The first maxim is “Actus non facit reum nisi mens sit rea” which means an act does not constitute guilt unless done with a guilty intention and

(b) The second maxim is “Furiosi nulla voluntas est.” which means the situation in which a person with mental illness has no free will. This means that an act does not constitute a crime unless it is done with a guilty intention called “mens rea” Hence, Section 84 in fastens no culpability on persons with mental illness because they can have no rational thinking or the necessary guilty intent.


 Legal insanity means a situation where at the time of the commission of any act which is illegal in the eyes of law, the person should be suffering from mental illness and also have a loss of reasoning power. This issue is clearly depicted in Section 84 of the Indian penal code as that person incapable of knowing:

  1. The nature of the act that he has done, or
  2. That he is doing what is either wrong or illegal
  3. The commission of the act is contrary to law.

Mere abnormality of mind or partial delusion, irresistible impulse or compulsive behavior of a psychopath affords no protection under Section 84 Indian penal code.

Surendra Mishra vs. state of Jharkhand

This is a landmark for section 84 of the Indian penal code in this case  the Apex Court has stated that an accused who seeks exoneration from liability of an act under Section 84 of the Indian Penal Code is to prove legal insanity and not medical insanity and the court also explained the ambit of this section.

Facts of the case: In this case the deceased Chandrashekhar chaubey was going in a car which was driven by Vidyut Kumar Modi after reaching to a destination Chandrashekhar chaubey asked the driver to stop the car and he called Shasdhar Mukherjee the owner of sulekha auto parts. the deceased (Chandrashekhar chaubey) started talking to him(Shasdhar Mukherjee) from inside the car and all of a sudden the appellant who is the owner of a medical hall came there with a pistol he pushed Shasdhar Mukherjee aside and fired the pistol on Chandrashekhar chaubey after which the driver fled away from the place where this crime happened and he immediately informed the family members of the deceased and left the deceased in the car itself on the basis of the facts a case was filed under section 302 of Indian Penal Code and section 27 of the arms act against the appellant

later on the appellant was put on trial for the Commission of offences under section 302 of Indian Penal Code and section 27 of the arms act the plea of the appellant was that by the virtue of unsoundness of mind the act committed by him comes within the exception under section 84 of the Indian Penal Code and therefore he cannot be held liable for the act done by him the trial court and later the High Court also rejected the plea of the appellant.

In this case the court said that for taking the defense of insanity or the defense of unsound mind under section 84 of the Indian Penal Code it must be established that the act committed are not offence and the person taking the defense is required to prove that at the time of Commission of the act the accused by the reason of unsound mind was incapable of making difference between wrong or right, legal or illegal nature of the act in the present case after the investigation it was made clear that immediately after the appellant had shot dead the deceased he then threatened vidyut Kumar ( the driver of the deceased) and he also ran away from the place of occurrence and he threw the pistol by these acts of the appellant it can be made clear that he was well known that whatever he has done is wrong and illegal. He (the appellant) was running a medical shop and came to the place of occurrence and shot dead the deceased had the appellant been the person of unsound mind it may not have been possible for him to run a medical shop and the court held the appellant libel under the section 302 of Indian penal court and section 27 of the arms act.


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