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  • The origins of the “Insanity defence” trace back centuries, with legal precedents such as “The McNaughten Rule of 1843” in England. 
  • Section 84 of the Indian Penal Code (IPC) establishes the insanity defence, affirming that if a person, due to a mental unsoundness, cannot comprehend the nature or unlawfulness of their actions, those actions are not considered criminal offences.
  • The insanity defence relied on legal principles rather than “Clinical diagnosis”. Simply having a mental disorder isn’t enough for this defence; what matters is whether the individual, due to their mental state couldn’t grasp the nature of their actions or differentiate between right and wrong.


In the domain of criminal law, the terms “Unsoundness of mind” and “Insanity” are often used interchangeably, although with variations across different legal jurisdictions. An important principle in criminal law that demands the establishment of two pivotal elements to establish ‘Guilt’ – Mens Rea (the guilty mind) and Actus Reus (the wrongful or unlawful action). The legal maxim “Actus Non-Facet Reum Nisi Mens sit Rea” emphasizes that both the action and the intent must concur to constitute a crime.

Hence, an individual cannot be held liable solely for malicious intent or wrongful deeds; rather, both components must align to prove guilt. Criminal liability arises only when an individual possesses full awareness of the nature of their actions and undertakes them of their own volition and consent. 

Within the framework of the Indian Penal Code, Section 84 found within chapter IV, which addresses "General exceptions”. This section encompasses provisions that offer valid defence to exempt individuals from criminal liability. Section 84, in particular, extends immunity to individuals deemed of unsound mind. 

Suppose an individual lacks soundness of mind to an extent where they cannot figure out the legality of their actions. In that case, they may invoke the insanity defence to avoid criminal responsibility. This defence relies on demonstrating that the individual could not comprehend the nature of their actions due to their mental condition. 

The landmark case of “McNaughten” (also known as the rule of unsoundness of mind as a defence) set the standard for determining insanity, establishing that individuals are presumed sane unless proven otherwise. To prove insanity, the accused must demonstrate a lack of understanding regarding the nature and consequences of their alleged actions therefore this case established the “knowing” test for insanity, emphasizing the importance of the individual's awareness of the rightness or wrongness of their actions. 

In another case “Dayabhai Chhaganbhai Thakkar V. State of Gujarat”, this case was a “severe” case – the accused fatally stabbed his wife 44 times – the Supreme Court, in this case, concluded that the evidence was insufficient to prove the accused's insanity at the time of the offence. The court stressed that the level of mental unsoundness must be such that the accused is completely unaware of the nature of the act they are committing. 


Unsoundness of mind as a legal defence goes back to early centuries, but it was not until the past three centuries that it gained ‘Formal’ legal recognition. The historical trajectory of insanity law can be traced to the 1700s. The first significant case in the development of insanity law is “R V. Arnold (1724)”, where Edward Arnold’s attempt to harm Lord Onslow brought attention to the issue, “Arnold, was suffering from a mental disorder, prompted Justice Tracy to remark: if he was under the visitation of god and could not distinguish between good and evil, and did not know what he did, though he committed the greatest offence, yet he could not be guilty of any offence against any law whatsoever”.

This particular case introduces the very notion that “individuals suffering from unsoundness of mind” could prove immunity in their case if they were unable to differentiate between good and evil or comprehend the nature of their actions, and this led to the development of the first test “Wild Beast Test”. McNaughton’s rule also known as the “M’Naughten Rule”, is a pivotal legal standard utilized to assess an individual’s criminal culpability based on their mental state at the time of an offence. Originating from the landmark case of “R V. McNaughton in 1843”, this rule provides clear guidelines for determining insanity. Under McNaughton’s rule, an individual may be found not guilty because of insanity if, during the commission of the offence, they suffered from a mental disorder that resulted in the following terms:

  1. Inability to comprehend the nature and consequences of their actions: they could not understand the nature of their actions or the potential outcomes.
  2. Lack of awareness regarding the moral or legal wrongfulness of their actions: their mental condition prevented them from distinguishing between right and wrong, leading them to believe their actions were justified or legal genuinely. 

The onus of proof rests with the defence to demonstrate the existence of a qualifying mental disorder as outlined above. If the defence successfully establishes that the accused meets the criteria of McNaughton’s rule, they may be acquitted on grounds of insanity.

The second test emerged in the case of “Hadfield’s Case (1800)”, where a man named Hadfield, who left the army due to insanity, was tried for treason after attempting to assassinate King George III, his defence led by Lord Thomas Erskine, argued that Hadfield’s actions were driven by an insane delusion, thus absolving him of guilt. This led to the development of the second test “Insane Delusion Test”.

In the case of “Bowler’s Case (1812)”, the third test was established where Justice LeBlanc directed the jury to assess whether the accused, at the time of the offence, could discern right from wrong or was under the ‘influence of an illusion’. After Bowler’s case, courts increasingly emphasized the accused’s ability to distinguish right from wrong, although with some ambiguity in application.


In India, the defence of insanity finds its legal footing under section 84 of the Indian Penal Code. This provision offers an avenue for individuals with unsound minds to evade criminal culpability. It stipulates that if, at the time of committing an act, a person was incapable of understanding its nature or discerning its wrongfulness due to unsoundness of mind, then that act is not deemed an offence.

Section 84, aligned with fundamental principles of criminal law, reflects the maxim “Actus Facit Reum Nisi Mens Sit Rea”, which asserts that an act does not incur guilt unless accompanied by a guilty mind or criminal intent. 

Thus, when an offence is perpetrated by an individual proven to be sound of unsound mind, it is assumed that the accused lacked the capacity for rational thought or intent necessary to commit the crime, absolving them of criminal liability. 

Section 84 bears resemblance to the M’Naghten rules presumes sanity unless proven otherwise and requires a defect of reason caused by a “disease of the mind”, Section 84 does not explicitly mention “quality” or “contrary to law”. Nonetheless, Indian courts often interpret Section 84 in light of the principles laid down in the M’Naghten case. 

Legal precedents, such as “Hazara Singh V. The State”, introduce the concept of “furious nulla voluntas est”, implying that a madman lacks will. Here, “madman” is construed as a mentally ill person. However, not all individuals with mental disorders can automatically avail of this defence. In another case “Bapu V The State of Rajasthan” clarified that it is “legal insanity”, not “medical insanity”, that must be established. 

Furthermore, subsequent legal developments underscore that mere eccentricity of mind, common among many offenders, does not equate to unsoundness of mind. What necessitates proof is cognitive impairment preventing the comprehension of the wrongful nature of one’s actions. 

In another case of “Dulal Naik V. State (1987)”, McNaughton's rule was construed alongside Section 105 of the Indian Evidence Act, which presumes a person to be sane unless proven otherwise, with the burden of proof resting on the accused. It's crucial to note that unsoundness of mind must be present at the time of the offence itself; conditions before or after do not suffice as a defence of insanity. 


Indian Penal Code:- Section 84 – Act of a person of an unsound mind

“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.”

Essentials of Section 84 of the Indian Penal Code: 

To invoke the defence of “unsoundness of Mind”, specific conditions must be established and demonstrated in court. Firstly, the individual must be proven to be of unsound mind at the time of the act. Secondly, they must be incapable of comprehending:

  • The precise nature of the act they committed, 
  • That the act violates the law, or
  • That the act is morally incorrect

This incapacity to understand must be solely attributable to their unsoundness of mind. Furthermore, this lack of comprehension must exist at the time the offence was committed. These criteria must be convincingly proven in court beyond a reasonable doubt.  To invoke the defence under this section, it's insufficient to merely claim insanity. Rather, based on the facts and circumstances of the case, the burden lies on the defendant to prove before the court that, at the time of the offence, they were suffering from unsoundness of mind, rendering them incapable of comprehending the nature and consequences of their actions. 

It's crucial to recognize that the terms “unsoundness of mind” and “insanity” are synonymous, with the former used in Indian law and the latter in English law. However, the drafters of the Indian Penal Code 1860 deliberately opted for the phrase “Insanity of Mind” to broaden the scope of the provision, encompassing a wider range of mental conditions.  

The legal maxim “Non compos mentis” is often employed to describe an individual with an unsound state of mind, signifying “not of sound mind”. 

  1. Unsoundness of mind can manifest in two forms: Permanent unsoundness of mind: in this situation, an individual’s cognitive abilities and mental faculties are permanently impaired due to psychological or mental issues. 
  2. Temporary unsoundness of mind: here, an individual experiences a temporary loss of motor skills and cognitive capacity, often stemming from factors like intoxication or drug consumption. This distinction underscores the varying nature and duration of unsoundness of mind, influencing the assessment of criminal responsibility under the law. 

Evidence Act:- Section 105 – Burden of proving that case of accused comes within exceptions 

“When a person is accused of any offence, the burden of proving the existence of circumstances bringing the case within any of the General Exceptions in the Indian Penal Code (45 of 1860), or within any special exception or proviso contained in any other part of the same Code, or in any law defining the offence, is upon him, and the Court shall presume the absence of such circumstances.”

In criminal cases, when an individual faces charges, the responsibility falls upon them to demonstrate the circumstances that justify their actions under any general exceptions outlined in the Indian Penal Code or specific statutes. Under this provision, the prosecution’s role is limited to proving the accused’s guilt; once established, the burden shifts to the accused. This distinctive aspect applies solely to criminal proceedings. accordingly, as per Section 105 of the act, the accused bears the burden of presenting evidence to counter the allegations. This principle is often termed the reverse onus clause. 


Section 84 of the Indian Penal Code outlines the legal standards used to determine criminal responsibility, which differs from medical criteria. The absence of intent can stem not just from a lack of understanding or maturity, but also from a pathological mental condition. This condition, which absolved one from criminal culpability, is viewed differently in medical and legal contexts. Medically, it could be argued that anyone engaging in criminal behaviours exhibits signs of insanity and should be exempt from accountability. However, legally, an individual is considered sane if they can distinguish between right and wrong and understand that their actions violate the law. 

The Supreme Court has ruled that not all mentally ill individuals are exempt from criminal liability. To claim immunity from a criminal case, a person must demonstrate legal insanity at the time the crime was committed. Simply being mentally ill does not automatically absolve one of criminal responsibility. There’s a distinction between legal insanity and medical insanity. The court emphasized that Section 84 of the Indian Penal Code, which grants immunity from prosecution to those of unsound mind, requires the accused to prove their insanity, as stipulated in Section 105 of the Indian Evidence Act.

In a landmark case of “Hari Singh Gond V. State of Madhya Pradesh”, the Supreme Court noted that Section 84 of the Indian Penal Code outlines the legal standard for determining responsibility in cases involving alleged mental insanity. However, the term ‘Insanity’ lacks a precise definition and encompasses various degrees of mental disorder. Therefore, not every mentally ill individual is automatically exempt from criminal responsibility. It's crucial to differentiate between legal insanity and medical insanity. Courts focus on legal insanity rather than, medical interpretations. 

In the case of “Kamala Bhuniya V. West Bengal State”, the accused was charged with her husband’s murder using an axe. She claimed “Insanity” at the time of the incident, and initial reports by the investigating officer supported this claim. The prosecution failed to arrange a medical examination for the accused and couldn’t establish a motive for the murder. Moreover, the accused displayed no attempts to flee or conceal the weapon. As a result, the accused was deemed to benefit from Section 84, proving insanity at the time of the offence. Consequently, she was found guilty of culpable homicide and not murder. In another landmark case “Surendra Mishra V. State of Jharkhand”, it was emphasised that not every individual with a mental illness is automatically exempt from criminal liability. Similarly, in another case of “Shrikant Anandrao Bhosale V. State of Maharashtra”, the Supreme Court highlighted that in determining the offence under Section 84 of the IPC, the totality of circumstances, as evidence, should be considered. 

It's crucial to establish the unsoundness of mind at the time of committing the act. While Section 84 does not explicitly use the term “Insanity”, courts focus on the mental state of the accused at the time of the offence. In the case of “Rattan Lal V. State of Madhya Pradesh”, the court established that the crucial moment to determine an unsound mind is at the time of the offence. The behaviour preceding, accompanying, and following the crime is relevant in assessing the accused’s mental condition. 


In conclusion, the intricate interplay between legal standards and medical criteria surrounding the insanity defence underscored the nuanced nature of criminal responsibility within the Indian legal framework. From the historical roots embedded in landmark cases like McNaughten to the contemporary interpretations of Section 84 of the Indian Penal Code, the evolution of legal principles governing unsoundness of mind as a defence reflects a careful balance between justice, accountability, and compassion for those affected by mental illness. 

The Indian legal system, drawing from global precedents while adapting to local contexts, has established clear guidelines for invoking the insanity defence. Section 84 of the Indian Penal Code, provides a legal avenue for individuals with unsound minds to seek exemption from criminal culpability, but this privilege necessitates a rigorous demonstration of incapacity to comprehend the nature or wrongfulness of one’s action at the time of the offence. 

Moreover, the burden of proof rests squarely on the accused, emphasizing the importance of thorough evidence and contextual understanding in adjudication cases involving mental health considerations. Through landmark judgements and legal precedents, courts have underscored the need to differentiate between legal insanity and medical diagnoses ensuring that not every individual with a mental disorder is automatically absolved of criminal liability.

Ultimately, in the pursuit of justice, it remains imperative for the legal system to navigate the complexities of mental health with sensitivity and expertise by upholding the principles of fairness, equity, and individual rights, the Indian legal framework continues to evolve, ensuring that justice is served while safeguarding the dignity and well-being of all individuals, including those grappling with mental illness. 

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