Insanity refers to "unsoundness of mind "or a state of mental ailment from which a human being suffers either temporarily or permanently. It is also known as some mental disorder from which a person is suffering at the time of commission of the offence. Under Section 84 of the Indian Penal Code, Insanity is a defense which is available legally to an Accused person and can be raised by him in the court of law during the trial.

This Unsoundness of mind should be of such nature that by reason of Unsoundness of mind the person should not be able to understand the nature of the act or that whatever act he is doing is either wrong or contrary to law.

Origin of Insanity

The insanity has been used as a defence from many centuries but it took a legal status from the last three centuries. The first case which dealt with it was R v. Arnold (1724) in which Arnold was suffering from a mental disorder and this mental disorder was present at the time of commission of the offence. He wound Lord onslow and tried to kill him; later he was tried for the same in the court of law.

There are several tests evolved to determine the test of insanity present in the accused these tests include Wild beast test, Insane Delusion Test. The most important and crucial test is the right and wrong test formulated in R v. Mc NaughtenCase which are also known as Mc Naughten Rules

Why is Insanity a Defence under Indian Penal Code?

Insanity is recognised as a defence under the Indian Penal Code because the Mens Rea is absent which means the guilty act to commit a crime is absent. The word Mens Rea here means the guilty intention or Knowledge or even Reason To Beleive. The well recognized maxim "Actus NON Facit Reum Nisi Mens Sit Rea" which means an act cannot be committed unless accompanied by a guilty mind.

If the intention to commit the crime or an offence is absent at the time of the commission of the offence then how can we punish the Person Accused of committing that crime?

"Where there is no will to commit an offence, there can be no just reason to incur the penalty". - Sir Mathew Hale.

The reason here for commission of offence is the unsoundness of mind or a suffering of mental ailment and due to that unsoundness the Accused if not able to understand the nature of the Act or whatever he is doing is wrong or contrary to law the person will be excused for any offence if he commits under Section 84 of Indian Penal Code, 1860.

Legal Insanity & Medical Insanity

Legal Insanity is alone excusable and Medical Insanity is not a defense at all in the eyes of law. It means if the person is suffering from Medical insanity and he commits a crime then he will definitely be punished under the Indian Penal Code or any other law in force the Court deems fit but if that person is suffering from legal Insanity then he can definitely take the defence of legal insanity under Section 84 of the Indian Penal Code. Medical insanity is just unsoundness of mind under section 84 of the IPC.

However legal Insanity has a wider scope it means that by reason of unsoundness of mind if the person is not able to understand the nature of the act or whatever act he is doing is wrong or contrary to the law then only it will be called legal Insanity and will be excusable in the eyes of law. In the case of Surendra Mishra v. State of Jharkhand 2011 it was ruled that an Accused needs to prove Legal Insanity and not Medical Insanity.

Conclusion
The Accused in order to take the defence of Insanity has to prove Legal Insanity and not Medical Insanity. The Accused just has to Rebut the presumption of court by taking this defence. The Accused just has to raise a "preponderance of probability" in the mind of the sitting Judge and if he is successful in raising this probability in the mind of Judge then he might be excused from the offence for which he is charged.

This Insanity must be present at the time of commission of the offence and if at the time of commission of the offence the Insanity is not present then the defence of Section 84 under IPC is not available to the accused and he will be punished for the offence charged.