Insanity as a Defence: Critical Analysis


Insanity is a state of mind in which person behaves in an absurd and unreasonable manner. It is one among the general exceptions to criminal prosecution. The question of legal insanity relies more on “responsibility” than on “facts”. Nothing is an offence committed by a person, who, at the time of doing it, by reason of unsoundness of mind was incapable of understanding the nature or consequences of the act[1]. Section 84 of Indian Penal Code, 1860 deals with the “act of a person of unsound mind”. The underlying principle is that a person, who is of unsound mind at the time of committing the offence, does not have the ability to think rationally and distinguish between right and wrong.

 In states that allow the insanity defense, defendants must prove to the Court that they didn’t understand what they were doing; failed to know right from wrong; acted on an uncontrollable impulse; or some variety of these factors[2]. This article would be an earnest approach to outline the history of insanity as a defense, the basic ingredients of section 84 IPC, circumstances under which the benefit of this exception can be availed and the tests of insanity.


The first treatise that identified insanity as a defense in criminal prosecution dates back to the 1581 English legal treatise stating that, “If a madman or a natural fool, or a lunatic in the time of his lunacy” kills someone, they can’t be held accountable[3]. Further, the “wild beast test” was introduced in the 18th century. According to this test the accused was not to be convicted if they understood the crime no better than “an infant, a brute, or a wild beast.” However, the Courts no longer use terms such as “wild beast or brute”. In India, basis of the concept of legal insanity under Section 84 of Indian Penal Code was the M’Naghten rule. This rule was formulated in 1843.

Key ingredients of insanity as a defense

  • Persons of “unsound mind”

There are four categories of persons of unsound mind. They are as follows:

  1. An idiot- person with abnormal mental capacity by birth.
  2. One made so by illness- such persons are excluded from criminal liability if they act under the impact of the disorder.
  3. Lunatic or a madman- person affected by mental incapacity at certain periods or at regular or irregular intervals.
  4. One who is drunk- abnormality due to exorbitant and habitual drinking.
  • At the time of doing it

To establish defense under insanity, the person must have acted under the influence of his mental disorder and did not know the nature of the act or did not know what he was doing was wrong. The fundamental principle of criminal liability is “Actus Non Facit Reum Nisi Mens Sit Rea”, which means an act coupled with a guilty mind constitutes a crime. In the case of insane persons, the concept of guilty mind is not present because they are not doing it with free will.

  • Unsoundness of mind

It is only unsoundness of mind which naturally impairs the cognitive faculties of the mind that can form a ground of exemption from criminal responsibility[4].

When can a person avail the benefit of insanity as a defense?

This would be dependent on the circumstances that preceded the act. In Ashiruddin Ahmed v. R[5], the accused kills his five year old son as he was demanded to do so in dream by someone in paradise. After committing murder he confessed to his uncle. In this case the Court was of the opinion that the accused is entitled to the benefit under Section 84 of IPC as he was unaware of the fact that it was wrong. But the Supreme Court in subsequent judgements held that merely because the son has been sacrificed by the accused, which no person in his right senses will do, the defense of insanity cannot be allowed[6].

In Dahyabhai Chhanganbhai Thakkar v. State of Gujarat[7],Kalavati was married to appellant in 1958. On 9 April 1959, she was killed by the appellant with a number of wounds. Neighbours heard her cry and collected in front of their room. The trial Court did not accept the plea of insanity and higher Court confirmed the conviction. On an appeal to the Supreme Court it was held that the presence of weapons in the room, bolting the room from inside, reluctance to come out of the room and large number of wounds given to the wife clearly indicated a pre-planned and vengeful move by the accused. Hence defense of insanity was not accepted.

In Hazara Singh v. State[8], accused suspected his wife of infidelity and caused her death by throwing acid upon her. He was not excused under the defense of insanity. Through these cases it can be surmised that to be benefitted by the defense of insanity the accused must not be in a state of mind to know that what he did was illegal or wrong. Here, the word “wrong” means legal wrong and not moral wrong. Moreover, the burden of proof is on the accused to prove the same.

Distinction between legal insanity and medical insanity

Proof of legal insanity is required to plead defense of insanity. Medical insanity is purely a biological aspect which deals with the mental illness and has nothing to do with law. On the other hand, legal insanity has more to do with the gruesome or unnatural condition of the person’s mind while committing an offence. It is a legal concept and has nothing to do with psychiatry. It can also be explained as the condition where the individual lacks proper thinking or cognitive skill. Every person who is suffering from mental illness is medically insane but may or may not be legally insane.

This distinction is best explained under Surendra Mishra v. State of Jharkhand[9]: every person who is suffering from mental disease is not ipso facto exempted from criminal liability, the onus of proving insanity or unsoundness of mind lies on the accused on preponderance of probabilities. To discharge the onus, the accused must prove his conduct prior to offence, at the time or immediately after the offence, with reference to his medical condition. Whether the accused knew that what he was doing was wrong or it was contrary to law is of great importance and may attract culpability despite mental unsoundness having been established[10]. The debate over considering medical insanity over legal insanity as the ground for exemption under the defense of insanity is still continuing among the medical and legal experts.

Test of insanity

I. M’Naghten rule:This test for insanity was developed in the M’Naghten case[11]. The facts of the case are: doctors diagnosed Mr M’Naghten with “persecution mania”. One day he shot one Mr Drummond, imagining him to be the Prime Minister of England. Mr M’Naghten thought that the Prime Minister was responsible for all his failures and misery. Witnesses stated that the crime was impelled by an uncontrollable impulse.

They were of the opinion that he was insane. The accused was excused on the ground of defense of insanity. The two tests were: whether the accused knew the nature of the act and whether he was aware of the fact that it was forbidden by law. This rule is the basis of defense of insanity under criminal law. This test is preferred over other tests of insanity. However, it was criticized for focussing on the moral aspects. Even if an insane person is fully aware of the nature and consequences of the act he might perform it due to his mental instability. Under such situations the test might prove to be wrong.

II. Irresistible impulse test: This test applies when the accused was unable to control his impulse reaction due to mental disorder. Under some situations, irresistible impulse test was considered to be more advantageous than M’Naghten’s rule.

III. Durham rule: Also known as “product defect rule” is where the accused is not convicted because of mental illness at the time of committing the offence. This test was considered very broad that there can be a high probability of misuse. Therefore, it is not much preferred over the other tests.

IV. Modern Penal Code test: Accused fails to understand the criminal nature of the act, or was not able to act within the boundaries of law due to a mental disorder.


The author opines that the idea behind criminal prosecution is to eliminate crime and build peace in the society. The defense of insanity was always interpreted based on the M’Naghten’s rules. The facts and situations of each case differs and it is indeed doubtful as to whether all these cases would necessarily fit in under M’Naghten’s test of insanity. Moreover, the concept of medical insanity may also become relevant in many cases. In such cases psychiatry may serve as an aid towards a progressive approach. It is indeed necessary to include the advancements in medical science within the boundary of law, especially in areas such as exemptions due to insanity. Henceforth, the aspect of insanity as a defense can be strengthened and widened without making it prone to misuse.

[1] Indian Penal Code, 1860 S.84


[3] ibid

[4] Kalicharan v. Emperor, 1946 SCC OnLine MP 99: ILR 1947 Nag 226: 1947 Cri LJ 377.

[5] Ashiruddin Ahmed v. R., (1949) 50 Cri LJ 255 (Cal).

[6] Paras Ram v. State of Punjab, (1981) 2 SCC 508: 1981 SCC (Cri) 516.

[7] AIR 1964 SC 1563: (1964) 1 Guj LR 911.

[8] 1957 SCC OnLine P&H 99: 1958 Cri LJ 555.

[9]  AIR 2011 SC 627 : (2011) CriLJ 1161.


[11] R v M’Naghten (1843) 8 E.R. 718; (1843) 10 Cl. & F. 200


  1. B.M. Gandhi’s Indian Penal Code: K.A. Pandey (4th ed)
  2. Gaur KD. Textbook on the Indian Penal Code. New Delhi: Universal Law Publishing; 2009.
  3. Math, S. B., Kumar, C. N., & Moirangthem, S. (2015). Insanity Defense: Past, Present, and Future. Indian journal of psychological medicine, 37(4), 381–387.

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