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The defence of "unsound mind": Meaning, Rules and Cases

Updated: Aug 2


An illustration of the mind of an insane person

It is a well-settled principle of criminal law that all crimes are not absolute in nature, and all such offences may not, therefore, satisfy or fulfil the essentials of a criminal act. This is especially true in exceptional cases, where the crime or offence committed was not intended to be committed, or there was no knowledge of its commission whatsoever.

Such circumstances are delineated under Chapter IV of the Indian Penal Code, 1860 named "General Exceptions".

Thus, to summarise the object of including Chapter IV or general exceptions as a separate chapter was two-fold-

  • To specify the circumstances or situations under which a person accused of a certain offence may escape liability or deter it.

  • To provide an easier understanding of the offences, so that there is no repetition of exceptions with explanations of different crimes.


Illustration: A scrambled brain (insane person)

To commit a criminal offence, mens rea is generally taken to be an essential element of crime.

It is said by – furiousus nulla voluntus est, which implies- a person suffering from a mental disorder cannot be said to have committed a crime, as he does not know about what he is doing.

Section 84 of the Indian Penal Code, 1860 provides a defence to such persons and acts from being punished. This Section provides that nothing in this Section shall be construed as an offence, which is committed by a person who-

At the time of doing such act, by the reason of unsoundness of mind, is incapable of knowing-

  1. The nature of the Act

  2. That he is doing what is either wrong or contrary to the law.

From the above explanation, the following essentials can be construed-

  1. The act complained of, must have been committed by a person of unsound mind.

  2. The accused must have been suffering from unsoundness of mind at the time of the commission of the act.

  3. The accused must have been incapable of knowing the nature of his act or what he was doing was wrong, or contrary to law.


M'Naghten (Daniel McNaughton)

In 1843, after Daniel McNaughton’s case, the McNaughton Rules became a very important precedent for the law concerning the defence of insanity.

The M'Naghten rule (pronounced, and sometimes spelt, McNaughton) is any variant of the 1840s jury instruction in a criminal case when there is a defence of insanity:

"that every man is to be presumed to be sane, and ... that to establish a defence on the ground of insanity, it must be clearly proved that, at the time of the committing of the act, the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or if he did know it, that he did not know he was doing what was wrong."


  • In the case of Siddhapal Kamala Yadav v. State of Maharashtra, it was held that though the onus of proving unsoundness of mind is on the accused, it has been held that where during the investigation, previous history of insanity is revealed, it is the honest duty of the investigator to subject the accused to medical examination and place such evidence before the Court, and if it is done so, it causes a serious infirmity to the prosecution’s case and the benefit of the doubt has to be given to the accused.

In this case, the Supreme Court also observed that there is no definition of “unsoundness” of mind under the Indian Penal Code. The Courts have, however, mainly treated this expression as equivalent to insanity.

  • In the case of Bapu @ Gajraj v. State of Rajasthan, it was held that insanity is a term of varying mental disorders. Therefore, a distinction must be made between Medical and Legal Insanity. It is pertinent to note that Courts are only concerned with legal insanity and not medical insanity.

Persons of Unsound Mind are also referred to as non-compos mentis. There are generally 4 kinds of persons who may be included under this category-
  • An idiot

  • One made non-compos mentis by illness.

  • A lunatic or madman.

  • One who is drunk.

A person who is made non-compos mentis through illness is excused from liability in criminal cases, for such acts as are committed, under the influence of his disorder. To constitute an offence, the intent and act must concur, but in the case of a person of unsound, no culpability is fastened on them as they have no free will.

The Supreme Court in the case of Sherall Wali Mohammed v. State of Maharashtra, held that- mere abnormality of mind or partial delusions, irresistible impulse or compulsive behaviours of a psychopath affords no protection under Section 84.

Behaviour, antecedent, attendant and after the event, maybe relevant in finding the mental condition of the accused at the time of the crime, but not that remote in time.

The Supreme Court in the case of Dahyabhai Chhagganbhai Thakkar v. State of Gujarat, defined the Doctrine of Burden of Proof in the context of a plea of insanity, in the following propositions-

  1. The prosecution must prove beyond reasonable doubt, that the appellant had committed the offence with the requisite mens rea, and the burden of proving that always rests on the prosecution from the beginning to the end of the trial.

  2. There is a rebuttable presumption that the appellant was not of unsound mind, in the sense laid down by Section 84 IPC, 1860: the appellant may rebut it by placing before the Court all the relevant evidence- oral, documentary, or circumstantial, but the burden of proof on him, is higher than what rests upon a party to civil proceedings.

  3. Even if the appellant was not able to prove that he was insane, at the time of the commission of the crime/offence, the evidence placed by the appellant before the Court, or by the prosecution may raise reasonable doubt in the mind of the Court as regards to one or more ingredients of the offence, including mens rea of the appellant and in that case, the Court would be entitled to acquit the appellant on the ground that general burden of proof resting on the prosecution was not discharged.

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