Define: Insanity

Insanity, in legal terms, refers to a mental state in which an individual is incapable of understanding the nature and consequences of their actions or distinguishing right from wrong. The concept of insanity is relevant in criminal law proceedings, where it may be used as a defence to criminal charges.

The insanity defence typically asserts that the accused, at the time of committing the alleged crime, lacked the mental capacity to form criminal intent or to understand the wrongfulness of their actions. Insanity defences are complex and vary in their application depending on the jurisdiction and legal standards.

Several legal tests are used to determine insanity, including the M’Naghten rule, the irresistible impulse test, and the Model Penal Code test. These tests generally assess whether, due to mental illness or defect, the defendant was unable to appreciate the nature and quality of their actions or understand that they were wrong.

Successful assertion of the insanity defence may result in the defendant being found not guilty by reason of insanity (NGRI). Instead of facing criminal penalties, individuals found NGRI may be subject to involuntary commitment to a mental health facility until they are deemed no longer a danger to themselves or others.

The insanity defence is not frequently used and is subject to strict scrutiny by courts. It requires substantial evidence of mental illness or defect and may be difficult to establish. Additionally, the legal standards and procedures surrounding the insanity defence vary significantly depending on the jurisdiction.

It is widely accepted that there is a level of mental derangement beyond which one is not liable for criminal acts. It is also widely accepted that a person who is insane may not be fit to answer criminal charges, even if he was of sound mind when the offence was alleged to have been committed. These two claims of insanity will have to be supported in similar ways, and judged by similar standards, but they are legally different. Therefore see: Insanity defence and Insanity and unfitness to plead for further discussion of these variants.

In both cases, a defendant who claims insanity has the burden of proof, on the balance of probabilities.

This site contains general legal information but does not constitute professional legal advice for your particular situation. Persuing this glossary does not create an attorney-client or legal adviser relationship. If you have specific questions, please consult a qualified attorney licensed in your jurisdiction.

This glossary post was last updated: 29th March 2024.