M'Naghten Rule: Definition & History

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Victim Impact Statement: Examples

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:04 Legal Insanity
  • 0:26 Definition
  • 1:24 History
  • 3:32 Lesson Summary
Add to Add to Add to

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Login or Sign up

Lesson Transcript
Instructor: Benjamin Truitt
The M'Naghten rule forms the foundation of the modern insanity defense plea. The test was to determine if the defendant in a criminal case knew that his or her actions were wrong and illegal at the time of the act.

Legal Insanity

The prospect of murder seems like the device of an unsound mind. Sane and normal people do not normally kill and hurt one another, which begs the question: Why aren't all murderers found not guilty by reason of insanity? The answer lies in the difference between clinical mental illness and legal insanity.


One of the cornerstones of legal insanity is the M'Naghten rule, a test that determines whether or not a defendant is criminally liable for his or her actions if he or she suffers from mental illness.

The M'Naghten rule requires that, should a person who commits a crime be unable to recognize that the crime is morally or legally wrong due to mental disease or mental defect, they should be found not guilty by reason of insanity. This rule, as applied in English and American law, distinguished criminals based on their capacity to recognize right and wrong to determine legal sanity and not whether they had a mental illness. Consider the example of Ted Bundy who was clearly insane and a sociopath when he raped and murdered women. However, Bundy knew that what he was doing was wrong and that his actions were illegal. And he even tried avoiding capture. In this case, the M'Naghten test would find that, while clinically insane, Bundy was legally sane.


On a chilly London afternoon in 1843, Edward Drummond, the secretary of Prime Minister Robert Peel, was shot to death by Daniel M'Naghten. When apprehended by police, M'Naghten gave paranoid and delusional reasons why he shot Drummond. The court decided, in listening to the evidence, that M'Naghten was not able to understand the nature of the act he committed. M'Naghten was so delusional, he did not even recognize that he had done anything wrong. This formed the basis of the modern insanity defense, or the M'Naghten rule.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 160 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create An Account