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  • Writer's pictureBrain Booster Articles


Author: Manisha Bharathi R, III year of B.B.A.,LL.B. from Symbiosis Law School, Hyderabad


Insanity, derived in the 16th century, from the Latin word ‘insanitas’ or ‘insanus’, means unhealthfulness with respect to the mind. This piece of study focuses upon the theme of insanity as a defence under Criminal Law. The paper entails the various essentials necessary to constitute insanity and the various rules and tests available and used widely in order to confirm the applicability of insanity as a defence in particular scenarios. The first chapter in the article talks about the origin of this defence and how it has evolved for the modern times. The second chapter primarily gives out the factors of differentiation between medical insanity and legal insanity and then goes on to elucidate the characteristics required for legal insanity. The paper, then, entails a brief elucidation regarding the theory of diminished responsibility and the concept of being guilty but mentally ill. Further, the paper contains a description of the situation and judgment delivered in landmark cases relating to insanity in India. Additionally, the paper delves into a comparative aspect and explains the rules and tests for insanity as a defence under UK and US laws in comparison to what is prevalent in India.


Insanity can be defined under law as a disturbed or unsound state of mind that renders a person devoid of the mental capacity required to do an act, enter an agreement, authorise something etc.[i] This unsound state of mind allows the person an exemption from civil or criminal liability, which is why it is termed as defence of insanity under law. This logic is deduced from the legal maxim: “furiosus solo furore punitur”, which means that a mad man is punished by his madness alone and does not attract civil or criminal responsibility for his acts. The maxim of “Actus Non Facit Reum Nisi Mens Sit Rea” also finds application here. It means that an act does not find a person liable if the person does not possess a guilty mind. Guilty mind (Mens Rea) i.e., a blameworthy mental condition is an important element to constitute a crime and that will be lacking in a person with an unsound mind as he/ she is not aware of the nature of the act done or whether it is right or wrong. On the same lines is the maxim of “Furiosi Nulla Voluntas Est” which means that a mad man lacks free will. In law, this maxim can be interpreted as that “there must be as an essential ingredient in a criminal offence, some blameworthy condition of mind, and such condition of mind cannot justly be imputed to madmen who are under a natural disability of distinguishing between good and evil.”[ii]

From the criminal aspect, Section 84 of the Indian Penal Code (IPC) talks about the defence of insanity. It states that “Nothing is an offence which is done by a person who, at the time of doing it, by reason of unsoundness of mind, is incapable of knowing the nature of the act, or that he is doing what is either wrong or contrary to law.[iii] It is peculiar to note that this statute does not use the word ‘insanity’ but instead uses the phrase ‘unsoundness of mind’ which indicates insanity of mind.

Insanity as a defence in Indian law (Section 84 of the IPC) has M’Naughten’s Rule as its origin/ backing. For the application of the defence of insanity, it is necessary that two essentials be qualified:

  • The accused must have been in an unsound state of mind during the commission of the act.

  • The accused must not have known/ was incapable of knowing the nature of the act committed by him/ her.

  • He/ She must not have known or was incapable of knowing that the act committed was wrong or contrary to the law.

Section 84 of the IPC has not undergone any change since its inception. However, an attempt was made by the Law Commission of India in 1971, via its 42nd report to revisit the provision but no changes were inflicted. When it comes to the usage of this defence, burden of proof lies wholly with the defendant and the insanity or unsoundness of mind has to be proved beyond reasonable doubt. This paper will delve into the essentials for the use of the defence of insanity, tests and theories used in relation to it, its position in criminal law and the prominence of the defence in the US and the UK law along with the Indian scenario.

Literature Review

  • Randy Borum and Solomon M. Fulero, in their journal article, “Empirical Research on the Insanity Defense and Attempted Reforms: Evidence Toward Informed Policy[iv] clearly explain the application of the defence in criminal law. The authors state that the two important components to establish a crime are actus reus (action) and mens rea (intent). They also state that it is a general assumption that people act on their own, free will and are responsible for their acts. The defence of insanity, however, comes in as a defence at this juncture because the person committing the act can be affected by a mental illness which in turn affects his/ her cognitive abilities to an extent that it does not constitute the real intent and free will of that person. This state of being exempts the person from criminal responsibility for his/ her act. Further, the article goes on to explain that the widely used insanity defence standards are the M’Naghten Rules and the provisions of the Model Penal Code. The article explores various perceptions and misconceptions regarding the use of the said defence, tests for its application, usage in murder cases etc.

  • Richard J. Bonnie, in his journal article, “The Moral Basis of the Insanity Defense[v] particularly focuses on the importance of the availability of the insanity defence and why the burden of proof should be on the defendant/ accused. Further, the author analyses various tests and theories relating to the defence and states that a test of insanity, to decide on the exemption of liability for a mentally unsound person who has committed a crime, must focus on the accused’s “ability to appreciate the wrongfulness of his conduct.”[vi]

  • In the book “Ratanlal and Dhirajlal: The Indian Penal Code, 34th edition”[vii], the author, while discussing the essentials to be satisfied to avail the insanity defense as entailed under Section 84 of the IPC, states that this provision of the statute must be read along with Section 105 of the Indian Evidence Act, 1872. While this is done, the provision of the Evidence Act places the burden of proof on the defendant/ accused and it is pointed out that there is no conflict between the burden that rests on the prosecution to prove the case and the special burden that rests with the accused to avail the insanity defence. Further, the author gives detailed case analyses and comments on the defence through the chapter on Section 84 of the IPC in the book.

  • In the book “K.D. Gaur: Textbook on Indian Penal Code 7th edition[viii], the author introduces an interesting fact that Idaho, a state in the U.S. which is known to have created a good number of insanity defence tests itself, does not allow insanity as a defence to criminal charges. However, this restriction can allow expert medical opinion to provide a persuasive opinion on the mental state of the accused and how it must have been during the commission of the act. This indicates that the state allows conviction of possibly insane people who have the ability to analyse the rightness and wrongness of the act they commit.

  • Suresh Bada Math and two other authors in their journal article titled ‘Insanity Defense: Past, Present and Future[ix]’ explores the defence in a detailed manner. What attracts the reader’s attention is how the authors have elaborated upon the quintessential role that a psychiatrist can play in judging the mental condition of the accused. Since legal insanity and medical insanity differ from each other, the Courts till date haven’t placed advanced/ expert medical opinion in a stature of importance to determine insanity but a standard/ uniform procedure to decide upon the insanity of the persons who plead it via Section 84 of the IPC is very much required. Psychiatrists, who now deal with treatment of convicts (who were punished under the premise of Guilty but Mentally Ill) can be asked to certify mental illnesses of the accused and certify whether the person is mentally and emotionally balanced to go through the procedures of the Court to establish his innocence and avail the defence of insanity.


The first-ever case regarding the defence of insanity dates back to 1724. It was an English law judgment (R. v. Arnold[x]) which put forward the Wild Beast Test. The Wild Beast Test for insanity followed the logic that a person will be immune from liability for the act that was committed by him/ her on the premise that he/ she was not aware of the nature of the act or whether the act done was right or wrong.

Later, the Hadfield case of 1800 introduced the Insane Delusion Test which states that the person must have been in an insane delusion (false belief or apprehension that will not be perceived by a rational person) and that the said delusion must have to be proved as the reason for the commission of the crime.

After this came the Bowler’s case of 1812 which established a test in which the Court would have to determine whether the accused possessed the ability to determine whether his/ her act was right or wrong. This test, however, did not serve as a clear-cut indicator of liability.

The case of R. v. M’Naghten in 1843 explored the insanity defence in a detailed manner and entailed that the defence requires two elements:

  • Presence of mental defect (which can be a defect of reason or a disease of the mind).

  • Mental defect must have caused a cognitive impairment to the accused by which he/ she does not know the nature and calibre of the act done by him/ her.

The case also laid down rules for the application of the defence of insanity:

  • Generally, it is presumed that every man is sane and is aware of what he is doing and the responsibility that he holds for each of his acts, until proved otherwise.

  • If the accused was aware of what he was doing or had only a partial insane delusion, then he/ she will be held liable for the criminal act committed.

  • It must be clearly established that the accused had operated with an unsound mind.

  • To avail the defence of insanity, it must be proved that, at the time of the act, the accused was not aware/ did not have the capacity to be aware of the nature and consequences of his/ her act. He/ She did not know whether the act was right or wrong.

These rules laid down in the M’Naghten case constitute the ‘Right and Wrong Test’ which is the most important, accurate and widely followed test with respect to the application of the defence of insanity. This test, along with the case, happened to be the base for the formulation of Section 84 of the IPC.


Three important essentials (entailed by the author in the introduction of the paper) have to be satisfied in the case for the accused to be able to exempt himself from liability/ responsibility using the insanity defence. Out of the three essentials, the first one is that the unsound mind of the accused during the commission of the act must be established. To establish this, it is necessary that the insanity adheres with the definition of legal insanity and not mere medical insanity.

Difference between medical insanity and legal insanity

Insanity, as indicated under Section 84 of the IPC, means the lack or absence of maturity/ clear understanding of the act done and the ill state of mind (unsoundness). When it comes to unsoundness of the mind, the definition differs from the medical and legal points of view. Simply, it can be told that any person committing a crime is insane and so, can avail the insanity defence but not every form of mad, crazy or insane behaviour/ act acknowledged by law shall ensure exemption from criminal liability. This view was affirmed by the Apex Court when it said that “Every mentally ill person is not ipso facto exempt from criminal responsibility.

A distinction needs to be made between legal insanity and medical insanity.”[xi] The Supreme Court further held that legal insanity holds importance in a court of law while deciding liability and not medical insanity. For example: Partial insane delusion, sudden provocation to do a rash act, psychopathic behaviour etc do not attract exemption from criminal liability on the grounds of insanity as they do not constitute as incapacity of the person to be aware of the nature, rightness or wrongness of the act.

Predominantly, insanity is considered as a mental aspect. Even if a person is mentally/ medically insane, it is not necessary that he is legally insane too. Medical insanity can be mental illnesses like Alzheimer, psychotic behaviour, inability of the person to distinguish between fictionality and reality, mental deficiency that occurs due to age, accidents or injuries, low IQ (Intelligence Quotient) and other conditions similar to this. Conditions of medical insanity has the persons under medication but they have the capacity to make decisions of their own and be aware of the consequences of their act. Medical insanity takes into account the past behaviour and acts of the person.

Legal insanity, on the other hand, can consist of a combination of the any of the conditions mentioned above with the incapacity of the person to be aware of the nature, rightness or wrongness of the act. Legal insanity can be better described as a mental illness/ unsound state coupled with the absence of reasoning power. This condition must exist during the commission of the act, which in turn exempts the person from liability for the criminal act committed as it was committed by him/ her without knowledge of its nature and consequences.

The unsoundness of mind of the person immediately preceding and succeeding the act done will be a relevant fact to exempt liability.[xii] Furthermore, the opinion of a medical expert regarding the mental state and behaviour of the accused will not hold utmost or final binding on the Courts. Their opinion would be of a persuasive nature and the Judges will have to decide on the applicability of the defence of insanity with respect to the proof established by the accused himself and the facts pertaining to the particular case. In simpler words, “It is the totality of the circumstances seen in the light of the recorded evidence that would prove whether the offence was committed.”[xiii]

Incapable of knowing the nature of the act committed

The second essential to be satisfied is that the person must be incapable of knowing/ not aware of the nature of the act while committing it. To satisfy this essential, the accused must have been entirely oblivious to what he/ she was doing and the effects and repercussions of the same. This state of being of the accused would also mean that the accused is legally insane and he lacks the ability to judge the outcomes, quality, criminal nature of his/ her act.

It is not enough if the aforementioned aspects had just occurred but it must be successfully established by the accused in the court of law in order for him/ her to avail the defence.

Incapable of knowing whether the act was right or wrong or contrary to the provisions of law

To avail the insanity defence, the accused must prove that he/ she committed the act when he/ she was not aware whether it is right or wrong or contrary to law. For this essential to be satisfied, the accused need not be entirely insane. Even if the accused is informed/ well aware of the nature and consequences of his/ her act, a proof of his/ her inability to have the knowledge of whether the act committed is right or wrong is enough to apply the defence provision. By the word wrong, it can mean either legally wrong or both legally and morally wrong.

No matter whether the standard for consideration is either of the two mentioned above, if there surfaces any evidence or proof that indicates the attempt to hide, cover-up or conceal material items or facts that might help in establishing criminal liability, it automatically gives out the conclusion that the accused was aware of right and wrong and goes on to nullify M’Naughten’s rule.

Usage of the defence of insanity and related provisions/ concepts

The defence of insanity is usually pleaded in felony cases i.e., cases involving crimes with a higher degree of seriousness like murder, manslaughter, kidnapping, burglary etc. What comes across as a related concept to this defence is the concept of diminished responsibility.


The theory of diminished responsibility is a defence, which, if established, will hold the accused liable for culpable homicide/ manslaughter and not murder. This concept/ doctrine has been entailed in Section 2 of the Homicide Act of 1957. This statutory provision states that in a case where a person is found to have killed someone, he will be liable for a decreased degree of crime i.e., manslaughter and not murder if it is proved that the person suffered some mental defect whose influence caused him to do the criminal act, without him actually knowing the nature and effects of the act.


In relation to insanity, this is a verdict that is now frequently passed by the courts of law. In these kinds of cases, the person with a mental defect who committed the criminal act is not eligible to avail the defence of insanity as his condition does not match with the essentials to avail the defence. He is punished and in addition, given treatment for his mental condition while serving his term of imprisonment.


Ratan Lal v. State of Madhya Pradesh[xiv]

In this case, the appellant set ablaze the grass in a piece of land. He reasoned his act by saying that he burnt it and the onlookers could do whatever they wished. He was charged with Section 435 of the IPC which gives out punishment for persons causing mischief by fire coupled with an intent to sabotage the area. A psychiatrist was consulted and the expert confirmed that the appellant was a lunatic under the Indian Lunacy Act, 1912 and the report provided by the psychiatrist indicated that the appellant suffered from lunatic depression and needs therapy for the same. On these grounds, the trial court acquitted the appellant. The High Court, on the other hand, overruled the decision of the trial court and made the person liable for his act. The Supreme Court, on an appeal, analysed the case and ruled that the accused could take the defence of insanity under Section 84 of the IPC and acquitted the person. The reasons stated for the acquittal were the medical proof provided and the mental condition of the person at the time of committing the act. These established that the person was insane and was carrying out the act of mischief in an unsound state of mind (without reasoning or knowing the nature of his act).

Shrikant Anandrao Bhosale v. State of Maharashtra[xv]

In this case, a police constable hit his wife on the head with a stone, which in turn caused her death. The police constable was booked for murder. He pleaded the defence of insanity and produced before the Court, evidence of a historical mental illness in his family. The cause of this illness was not known and it was also brought to attention that the constable was under treatment for the same. He lacked motive to kill and no attempt was made by him to conceal or cover-up the criminal act.

Therefore, the Court declared that the constable was mentally defect and showcased incapacity to realise the nature of the act committed by him. The constable was freed from charges by successfully availing the defence of insanity under Section 84 of the IPC.

Sheralli Wali Mohammed v. State of Maharashtra[xvi]

In this case, the offender killed his wife and daughter using a chopper. He was booked for murder. There was a lack of motive on behalf of the offender and he did not make any attempt to flee or hide his act. When he pleaded the defence of insanity, the Court rejected the plea stating that mere lack of motive and absence of attempt to conceal facts is not enough to attract the defence of insanity. The defence can help in the exemption of liability only for those persons who have a mental defect and by reason of such defect are unable to comprehend the nature, consequences, rightness or wrongness of the act being committed by them.



English law, which provided the base for the emergence of Section 84 of the IPC, contains the defence of insanity as a valid defence in criminal law. M’Naughten’s rules from the English law judgment of R. v. M’Naghten form the foundation of the insanity defence. Before M’Naghten’s case, English Law had experimented with the defence of insanity through the Wild Beast Test and the Insane Delusion Test (explained under Chapter II of this paper), but M’Naughten’s rules have been considered as the most accurate and important ones with regards to the usage of the defence. As has been explained earlier from the Indian point of view, in the English circumstances too, the accused, in order to avail the defence of insanity must establish his unsound state of mind during the commission of the act which led to him being unaware or unable to decipher the nature, after-effects or the rightness or wrongness of the act being committed by him.

Irresistible Impulse

Irresistible impulse can be defined as a sudden provocation that incites a person to commit an offence. In Indian Law, irresistible impulse is not considered as a part of the defence of insanity. It does not adhere to the provisions of Section 84 of the IPC as well.

The Apex Court declared that losing self-control or an irrepressible inclination is not a defence under Indian law.[xvii] The Supreme Court, in another instance, adjudged that in a case where a murder is committed on the premise of an irresistible impulse and there being no motive to explain the murder, the defence of insanity cannot be availed[xviii] as there is no indicator hinting at incapacity of the accused to distinguish between right and wrong.

But, under English Law, certain instances with a combination of irresistible impulse and a mental defect and absence of reasoning power can come under the ambit of insanity, thereby attracting the defence under criminal law.


Similar to the Indian circumstances, law in America also had M’Naughten’s rules as the forerunner to determine liability in cases where the defence of insanity is pleaded. In addition to this, American Law had the Irresistible Impulse test that was established in 1884. Unlike India, in America, irresistible impulse when coupled with unsoundness of mind in certain circumstances can exempt the doer of the act from liability under the pretext of insanity defence. This view was upheld in the landmark case of Lorena Bobbit[xix]in 1993.

Durham Rule

Later, The United States started making use of the ‘Durham Rule’ or the ‘Product Test’ which was introduced in the case of Durham v. United States. The essentials of the Durham Rule are as follows:

  • Mental disease or weakness

  • Causation of crime through the mental disease

Initially, this case declared the existing tests of Right and Wrong Test (M’Naughten’s Rules) and the Irresistible Impulse Test as no longer useful. Later, it was realised that the existing tests can be used along with the new Durham Rule. Presently, the Durham Rule is followed only in New Hampshire because it is considered to have too broad a scope by other jurisdictions.

Substantial Capacity Test

USA has another test for the insanity defence which is termed as the Substantial Capacity Test. This test was propounded by the Model Penal Code created and published by the American Legal Institute in 1962. This Code assists the existing legislations in the U.S. in the field of criminal law. According to this test, the person committing the act must have a mental defect/ disease and that mental condition must facilitate a volitional act. In order to be exempted from criminal liability, the conclusion of this test must be that the person with the mental defect lacked a substantial capacity to recognise the criminal nature of the act done or adhere with the provisions of law.


The author, through this research paper, has studied and presented the defence of insanity in a criminal law viewpoint. How the defence originated, various tests for exemption of criminal liability, their usage presently, comparison of the Indian pointers with the UK and the US, similar concepts to the insanity defence and many more have been discussed in this paper. The modern era guarantees the misuse of the insanity defence to easily exempt liability when the accused actually happens to be aware of the consequences of his/ her act. To avoid misuse of the defence and to follow a standard procedure, Courts can approach the field of forensic psychiatry for aid. Experts from this field will be able to judge the medical (mental) condition of the accused and will also be able to differentiate between legal and medical insanity and help the Courts in the process of justice.

[i]Lexico, (last visited Oct. 8, 2021). [ii]Duhaime’s Law Dictionary, (last visited Oct. 10, 2021). [iii] Indian Penal Code, No. 45 of 1860, § 84, India Code, (1993), Vol.15. [iv] Randy Borum et. al., Empirical Research on the Insanity Defense and Attempted Reforms: Evidence Toward Informed Policy, 23 L. & Human Behavior, 375, 375-382 (1999). [v] Richard J. Bonnie, The Moral Basis of the Insanity Defense, 69 American Bar Association J., 194, 194-197 (1983). [vi]Id. [vii] 1, K. Kannan et. al., Ratanlal and Dhirajlal: The Indian Penal Code, 34th edition (LexisNexis 2020). [viii]K D GAUR, Textbook on Indian Penal Code (LexisNexis 2020). [ix] Suresh Bada Math et. al., Insanity Defense: Past, Present and Future, 37 Indian J. Psychol. Med. 381, 381-387 (2015). [x] R. v. Arnold (1724). [xi]Hari Singh Gond v. State of M.P., (2008) 16 SCC 109. [xii] Shrikant Anandrao Bhosal v. State of Maharashtra, (2002) 7 SCC 748. [xiii]Id., Ratan Lal v. State of M.P., (1970) 3 SCC 533. [xiv]Ratan Lal v. State of M.P., (1970) 3 SCC 533. [xv]Shrikant Anandrao Bhosale v. State of Maharashtra, (2002) 7 SCC 748. [xvi] Sheralli Wali Mohd. V. State of Maharashtra. (1973) 4 SCC 79. [xvii] Kannakunnummal Ammed Koya v. State of Kerala, 1966 SCC OnLine Ker 93. [xviii] Ganesh Shrawan Chaudhari v. State, (1969) 71 BOMLR 643. [xix] State v. Bobbitt, 178 Wis. 2d 11 (1993).


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