Non Compos Mentis

The Latin term non compos mentis translates as “not of sound mind.” In the legal system, the term is used to refer to an inability to think clearly, or to make decisions, usually due to mental illness. Someone who is non compos mentis may not be responsible for his or her actions. To explore this concept, consider the following non compos mentis definition.

Definition of Non Compos Mentis


  1. Not of sound mind
  2. Being incapable of managing one’s affairs


1600-1610       Latin

History of Non Compos Mentis

In medieval times, non compos mentis described a person’s actions as being related to, or caused by, some diabolical religious influence, or other mysterious phenomena. As civilization moved on into the 17th century, non compos mentis was viewed as insanity or madness. It became a legal term referring to actions influenced by a mistaken or confused idea or mental image.

Non Compos Mentis in Suicide

In historic times, the taking of one’s own life was seen as a spiritual crime – one which excluded the individual from being buried in consecrated ground. It also meant an automatic forfeiture of the individual’s estate or assets to the Crown. English law, however, applied one of two theories to the reasons someone might take his own life.

Felo de se is a Latin term that translates as “felon of himself,” and refers to a person who has killed himself. Because this is a serious crime – even though the “felon” was dead – he was punished by taking his estate for the government.

At one point, a defense of mental incapacity, or mental illness, was allowed. A defense of non compos mentis took away the stigma of sin, ascribing the motivation to an outside influence, such as demonic possession or magic, or to a mental state that could not be helped.

For example, non compos mentis might have been used as a defense if a man, who had been seen with violent mood swings, and had withdrawn from his social interactions, committed suicide. People – and more importantly the law – might have attributed the man’s odd behavior to possession. In such a case, the man’s wealth would be distributed in the normal probate procedure.

Non Compos Mentis Examples in Sentences

  1. Abbigail had never allowed him to get this close to her, except when she was non compos mentis – stone cold drunk.
  2. While Walter’s friends were found guilty of harassing and assaulting a fellow student, Walter was non compos mentis at the time, having consumed a large amount of alcohol.
  3. Having ruled that Betty was non compos mentis, the judge paved the way for her family to admit her to a mental hospital.
  4. The court found that Robert – who suffered from bipolar disorder – was non compos mentis, and could not be put on trial for murder. (In this example, non compos mentis is used in place of the more common term “temporary insanity.”)
  5. When Alice fell down the rabbit hole, she discovered the Mad Hatter, who was clearly non compos mentis.