McNaughten rule refers to a standard for judging legal insanity which requires that either an offender did not know what he or she were doing, or that, if he or she did, that he or she did not know it was wrong.

The McNaughten rule, also known as the right-wrong test, is a legal standard used in criminal trials to determine whether an individual is legally insane at the time of the crime. This rule was established in 1843 by the English court in the case of R v McNaughten and has since been adopted by many other countries, including the United States.

Under the McNaughten rule, a defendant can be found not guilty by reason of insanity if they were suffering from a mental illness or defect at the time of the crime and did not understand the nature and quality of their actions or did not know that their actions were wrong. The burden of proof is on the defendant to prove insanity, and this defense is not commonly used in criminal trials.

One example of the McNaughten rule in action is the case of John Hinckley Jr., who attempted to assassinate President Ronald Reagan in 1981. Hinckley was found not guilty by reason of insanity under the McNaughten rule, as he was suffering from schizophrenia at the time of the crime and did not understand the nature and quality of his actions.

Similar to the McNaughten rule is the irresistible impulse test, which is used in some jurisdictions in the United States. Under this standard, a defendant can be found not guilty by reason of insanity if they were unable to control their actions due to a mental illness or defect, even if they knew that their actions were wrong.

Another similar concept is diminished capacity, which is a defense used in some jurisdictions to argue that the defendant's mental state at the time of the crime prevented them from forming the specific intent required for the crime. This defense does not require the defendant to prove insanity, but instead focuses on the defendant's ability to form the necessary mental state for the crime.

Critics of the McNaughten rule and similar standards argue that they are overly simplistic and do not account for the complexities of mental illness and criminal behavior. These standards also place the burden of proof on the defendant and can be difficult to prove in court. Some have advocated for a broader definition of legal insanity that takes into account the defendant's mental state and capacity to control their actions.

In summary, the McNaughten rule is a legal standard used in criminal trials to determine whether an individual is legally insane at the time of the crime. Similar concepts include the irresistible impulse test and diminished capacity. While these standards have been criticized for being overly simplistic, they remain a critical component of the criminal justice system and are used to balance the need for justice with the need for compassion for those with mental illness.