Duhaime's Law Dictionary

Non Compos Mentis Definition:

Latin: Not of sound mind.

Related Terms: Lunatic, Mental Disorder, Mentally Ill, Mentally Retarded, Alieni juris, Competency, Insanity, Idiot, De Non Sane Memorie, Dotage

Also sometimes presented as non compotes mentis.

In law, a person with an unsound mind.

Formerly, synonymous with lunatic and, more recently, insanity.

The Interpretation Act of Newfondland 2013 defines non compos mentis as:

"... mentally disabled."

Ballentine's 1969 law dictionary:

"Non compos mentis: mentally incompetent. Having a mental condition approximating total and positive incompetency. Destitute of memory and understanding.... A person of unsound mind."

In Dexter v Hall, Justice Strong of the United States Supreme Court used these words:

"[A] lunatic, or a person non compos mentis, has nothing which the law recognizes as a mind, and it would seem, therefore, upon principle, that he cannot make a contract which may have any efficacy as such."

An article appearing in the Chicago Law Review proposed this background information:

"When it was desired to distinguish merely between the sane and the insane, and not between the lunatic and the idiot, a generic term covering both was used. In early texts the term de non sane memorie was common [Y.B. 8 Edw. II, 24 (1314); Cross v. Andrews, Cro. Eliz. 622 (K.B., 1598); see also statutes, I Rich. III, c. 7 (1483), and 23 Eliz., c. 3 (1581)]. Later on the term non compos mentis replaced this.

"We first noted this expression in the statute De Praerogativa Regis, c. 10. See the interesting entry in the Middlesex Sessions Rolls, 22 James I, entry of 29th July, 1625: "Anne Muskett late of the said parish spinster killed and murdered Clement Harrison, a girl of the age of 8 years by seizing the said Clement with both hands and throwing her in quoddam flumen vocatum the newe River. Acquitting her of murder, the jury found that she was a lunatic, and whilst non compos mentis had drowned the said Clement Harrison."

In 1628, in his Commentaries, Edward Coke wrote:

"Non compos mentis is of four sorts: 1. Idiota, which from his nativity by a perpetual infirmity is non compos mentis. 2. He that by sickness, grief, or other accident wholly loseth his memory and understanding. 3. A lunatic that hath sometime his understanding, and sometime not ... and therefore he is called non compos mentis, so long as he hath not understanding. Lastly (4) he that by his own vicious act for a time depriveth himself of his memory and understanding, as he that is drunken."


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