The McNaughton Rules

(By Andrew Garofolo)

Prior to the McNaughton Rules, there was no clear set way of dealing with the insane in the court room. In 1843, a man named Daniel McNaughton attempted an assassination on the Prime Minister, and accidentally shot the secretary of the Prime Minister. McNaughton suffered from what might be considered today as paranoia and delusions of prosecution. He believed the government was out to get him (Constanzo, 2004).

After a lengthy trial, McNaughton was acquitted of his actions because he was deemed “insane.” Thus, he was not held accountable for his actions. This ruling outraged the public, and provoked a redefinition of what “insanity” was. Therefore, the House of Lords met, and established the main idea that posed as the question, “did the defendant know what he was doing, or, if so, that it was wrong?”

A few basic parts to the McNaughton Rule:

  • There is a presumption, that the defendant is sane, and that they are responsible for their criminal acts.
  • At the time of the crime, the defendant must have been suffering from a “disease of the mind.”
  • If the defendant knows the nature of the crime, do they know what they did was wrong. (“United Kingdom House of Lords Decisions,” 1843).

In 1851, the McNaughton Rule was adopted in the US court system. There were several criticisms to the McNaughton Rule including:

  • In 1851, the McNaughton Rule was adopted in the US court system. There were several criticisms to the McNaughton Rule including:
    • There was medical irrelevance, making it not as valid.
    • There was ineffectiveness to distinguish between those who represent a public danger, and who do not.
    • There were problems with sentencing.
    • It did not permit complete and adequate testimony, making it less trusted.


Costanzo, M. (2004). Psychology Applied to Law.  Belmont, CA:Wadsworth/Thomson Learning

“United Kingdom House of Lords Decisions.” (1843) M’Naghten’s Case. UKHL J16 (19 June 1843). JISC, n.d. Retrieved from

1 thought on “The McNaughton Rules

  1. The McNaughton Rule recognized that in psychotic mental illness
    when one commits a crime, one may be unable to know that they
    are committing a crime and that it is wrong to do so is flawed.

    The clinically accurate rule should be that one is unable to appreciate the criminal harmfulness of their actions or even make the judgment that they are right or wrong. That is, if they were in their right mind the criminal actions would not have occurred. They can’t help it because they can’t grasp the seriousness of what they are doing and with treatment with reality support and they most often are intensely remorseful for what they have done.

    Civilization is currently going through horrible harm inflicted by those in psychotic mental illness states because the courts have been unwilling or unable to confront or provide for their treatment. If this is not corrected, the law will go down in history as enabling a pandemic of psychotic homicidal and suicidal states that are destroying centuries of progress in reining in psychotic aggression.

    Queen Victoria who asked for McNaughton rules in 1843 had a better grasp of psychotic mental illness than many lawyers, psychiatrists, and psychologists do now and she wasn’t either a lawyer or a psychiatrist.

    I am a retired award winning psychiatrist-psychoanalyst and forensic psychiatrist with extensive experience successfully treating treatment resistant schizophrenia.

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