1843 case of daniel mnaghten biography

Guideline governing legal pleas of insanity

The M'Naghten rule(s) (pronounced, and sometimes spelled, McNaughton) is a legal test defining the defence of insanity that was formulated by the House of Lords in 1843.

It is the established standard in UK criminal law.^[1]: 5 Versions have been adopted in some US states, currently or formerly,^[2] and other jurisdictions, either as case law or by statute.

Its original wording is a proposed jury instruction:

that every man is to be presumed to be sane, and ... that to establish a defence on the ground of insanity, it must be clearly proved that, at the time of the committing of the act, the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or if he did know it, that he did not know he was doing what was wrong.^[3]: 632

The rule was created in