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“ACTUS NON FACIT REUM NISI MENS SIT REA”. The Latin phrase is a popular maxim in criminal law which lays down the two basic constituents of a crime i.e., mens rea which is the mental aspect and


“ACTUS NON FACIT REUM NISI MENS SIT REA”. The Latin phrase is a popular maxim in criminal law which lays down the two basic constituents of a crime i.e., mens rea which is the mental aspect and actus reus which is the physical manifestation. This translates to the fact that to prove a person is liable for a crime requires the establishment of not only the guilty act but also the guilty mind which led to the commission of such a crime. Section 84 of the Indian Penal Code, 1860 deals with the general defence of ‘insanity’ which is an exception to the above-mentioned maxim. According to this section, “Nothing is an offence which is done by a person who, at the time of doing it, because 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”.  It is important to note that the word ‘insanity’ has not been used in the Indian Penal Code anywhere explicitly, instead the terms ‘mental unsoundness’ is attributed to this section. It is a strenuous task for the accused persons to show that although the actus reus element has been performed by them, the mens rea element is absent completely, implying that no crime per se has been committed. Since this section is part of the general exceptions, there is no mitigation in the sentencing by the Courts but complete absolvement of the accused from criminal liability even if there has been harm to a person or a property due to the actions performed by the offender who successfully takes this defence and proves the requisite criteria under it. 


To take this defence, one must prove that the person who committed the crime lacked the requisite mental element to comprehend the criminal nature of the act at the time of the commission act for which one needs to know the difference between medical insanity and legal insanity since a medically ill person cannot be automatically free from criminal liability as discussed in the case of  “Hari Singh Gond v. the State of M.P. (2008)”. The required ingredient for the Courts in such cases is that the presence of ‘legal insanity’. In a recent judgement of “Tufan Singh v. State of M.P.(2022),” the Court differentiated between medical insanity and legal insanity as follows – “Any person, who is suffering from any kind of mental weakness is called “medical insanity,” however “legal insanity” means, the person suffering from mental illness should also have a loss of reasoning power.” Legal insanity is the parameter that falls under the purview of this section, the onus to prove of which lies on the accused which involves showing lack of soundness of mind when the offence was being committed. In another case “Ram Bahadur Thapa v. the State Of M.P. (2021”), the judgement was inspired by the British M’Naughten rules which were created after the case of M’Naughten akin to which, there are two possible directions of enquiry. To claim the defence of insanity under Section 84 it must be proved that at the time of committing such an act, the accused was incapable of understanding the nature of it which may also be due to the presence of medical insanity or if the accused person did understand the nature of the act, the immorality or illegality of such an act was unknown to the person. To fulfil the second criterion, one must comply with one of the three sub–conditions as per the law which is in line with the M’Naughten Rules. It shall be proved by the accused that owing to unsoundness of mind 1) was unaware of the nature of act 2) knew the nature of the act but was oblivious to it being morally wrong or, 3) knew the nature of the act but did not know about its illegality. In essence, the cognitive, or moral incapacity of the accused person must be shown to claim this defence. “There can be no legal insanity unless the cognitive facilities of the accused are so completely impaired as to render the person incapable of understanding the consequences of the act.”. Therefore, it can be said that even if Courts look for the presence of ‘legal insanity’ in such cases, the existence of earlier ‘medical insanity’ may sometimes supplement the person who is taking this defence.


Thus, to put it simply, insanity in the legal domain has two meanings. One refers to medical insanity according to which a person may be suffering from a mental condition that a psychiatrist can diagnose. However, proving merely medical insanity does not provide a person immunity from criminal liability to avail which legal insanity has to be established to apply Section 84 as a general exception. Legal insanity implies the lack of cognitive understanding a person experiences at the time of the commission of an act, the nature of which cannot be comprehended by the accused. Even if there was the capacity to understand the nature of the act, it must be shown that the accused was unaware of the actus reus performed being an illegal or an immoral one. Nonetheless, this defence is not of a popular kind in India to evade punishments due to various reasons. As it is having mental issues is looked down upon in the country and even after this defence is utilised, the accused may be subjected to counselling or therapy at mental asylums and be kept under the supervision of medical professionals to cure the condition. The social stigma around it also makes it an unfavourable loophole for persons trying to use this defence. Some other limitations of this section are that it fails to define the domain of mental conditions which are recognised as per law thereby resulting in a restrictive interpretation of the section. Also, since the behaviour of the accused is evaluated to determine legal insanity, it becomes subject to judicial subjectivity in the Courts which might result in unfair verdicts.

Author(s) Name: Spandan Tikle (OP Jindal Global University, Sonipat)