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Insanity and the Law: How a 19th Century Test is Used to Prove Insanity Under Criminal Law

By Sanchali Bhowmik

Part IV of the Indian Penal Code (“IPC”) ranges from Section 76 to Section 106 IPC and
comprises the various general exceptions: from the acts of a minor to the unsoundness of the
mind of the persons. Section 84 IPC specifically discusses Insanity, or in a broader manner, the
unsound mind of an individual while committing a crime. This section explains that any act
committed by a person of an unsound mind will not be actionable and they won’t be held liable
for any offense while being in the state of insanity. The burden to prove the insanity would rest
upon the defendant (one who claims this defense) to prove that they weren’t able to understand
the consequences of their act and couldn’t distinguish between right or wrong owing to lack of a
sound mind. Hence, the presumption under this defense would be that the person was sane or of
a sound mind while committing the offense and the contrary would need to be proved by
Though the word or the meaning of ‘Insanity’ has not been explicitly stated in this section of the
IPC, it focuses on its aspects in a broader term by describing the exception of the ‘Unsoundness
of Mind.’ The concept of Insanity has been long known to the world and came into prominence
from the 1700s with the various tests that emergedHowever, in this article, we shall be
discussing the test that the Indian jurisprudence follows i.e. the Mc’Naughton’s test. The test laid
down in the case of R v Mc’Naughton (1843), is currently followed under Section 84 of IPC in
India. Apart from the Mc’Naughton’s Test, there are several other tests as well. The Wild Beast
Test and Insane Delusion Test is another. a person can demand immunity if, due to his
unsoundness of mind, he was incapable of distinguishing between good and evil and did not
know the nature of the act committed by him and this test is called the the wild beast test.
However, the Mc’Naughton’s Test has several important points of the other tests and hence is the
most efficient with respect to determining the state of mind of an individual. This test has been
the guiding light for determining the liability of a person of an ‘Unsound Mind’ and hasn’t been
modified since the time it was incorporated.
Mc’Naughton’s Rules:

The test laid down in the case of R v Mc’Naughton is the most extensive and the most accurate
test to determine whether the defense of insanity applies or not. In this case, Daniel
Mc’Naughton was under the insane delusion that the Prime Minister at that time Sir Robert Peel
was the sole reason for all his problems. Hence, he decided to kill the Prime Minister. However,
he mistook the Personal Secretary of the PM Mr. Edmond Drummond to be the Prime Minister
and subsequently killed him.
He tried to plead the defense of Insanity as he didn’t have the knowledge of the adverse
consequences of his actions and also couldn’t distinguish between right and wrong. The Fifteen
Judge Bench was constituted in the House of Lords to decide upon this case and while giving the
judgment they laid down some rules that came to be known as the Mc’Naughton Rules which
were as follows:
a. If a person has partial delusion and could understand to a reasonable extent what is right
or wrong, he/she won’t be able to plead the defense of insanity.
b. There is a presumption that the person committing the criminal offense is sane or prudent
and knows what he is doing.
c. To establish the defense of Insanity, Defendant must prove that at the time of the offense,
the state of mind of Defendant was such that he/she wasn’t capable of determining the
consequences of their acts.
d. If the person has sufficient medical knowledge and is familiar with the state of Insanity,
he/she isn’t allowed to give their opinion and it’s upon the jury to decide and determine
the various questions of law.

This test is currently followed in India and also in several other countries as it is very
comprehensive in itself and gives a strict definition of Insanity in Legal terms. Though efforts
were made to change these rules with time, these have not been modified in India till yet and are
followed just like they were from the very beginning.
Irresistible Impulse Test
This test was laid down in the 19th Century. It was based on the concept of moral insanity which
meant that a person can act with an unsound mind even for temporary periods and are otherwise
sane persons. This conduct is involuntary on the part of Defendant and generally arises
spontaneously in a given situation. As a result, they can’t be held liable even if they are generally
able to comprehend what is right and what is wrong.
The liability can also vary as per different facts and circumstances of the case. It is seen to be a
variation to the Mc’Naughton Rules but had several criticisms of its own due to which more
importance is given to Mc’Naughton’s Rules worldwide.
In the case of Parsons v State, the court held that though Defendant was prudent and generally
had the ability to distinguish between right and wrong, he lost his power to choose the same

under the duress of mental disease at the time of the incident. These were the general tests that
have been laid down over the years. From all these, while some aren’t followed currently, the
rules laid in Mc’Naughton’s case still hold a lot of relevance and are widely followed.

Position in India:
India follows the Mc’Naughton Rules as stated in the general exception of Insanity under Section
84 of the Indian Penal Code. The term ‘Insanity’ ,though, has not been defined in the section, yet
all provisions have been stated under the concept of the ‘Unsoundness of Mind’ that is a broader
term with Insanity only being a component of it.
It has been stated under this section that a person who committed a wrongful act won’t be held
liable if he didn’t have the knowledge of the nature of his act or couldn’t distinguish between
right and wrong due to the unsound mind. The elements under this section are as follows:

Sanchali Bhowmik, a 3rd -year law student (L.L.B Hons.) at Jindal Global Law School

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