Mental incompetence

In both civil and criminal matters, legal problems can occur when a person lacks mental competence or capacity.

Civil matters

People who are mentally incompetent cannot enter into legally binding contracts, nor can they make a valid will. If a document was entered into with a person who was not mentally competent at the time, the document can be set aside.

Under the Guardianship and Administration Act 1993 mental incapacity includes the inability of a person to look after his or her own health, safety or welfare or to manage his or her own affairs as a result of:

damage to, or illness, disorder, imperfect or delayed development, impairment or deterioration of the brain or mind, or
any physical illness or condition that renders that person unable to communicate his or her intentions or wishes in any manner whatsoever.

Criminal offences

If a person commits a crime but is mentally incompetent at the time, they are not guilty at law of committing the offence. This is the mental impairment defence.

A person is considered as mentally incompetent to commit a criminal offence if, when they committed the offence:

they did not know the nature and the quality of their conduct, or
they did not know that their conduct was wrong, or
they were unable to control their conduct.

This means that the person did not understand what they were doing, or the consequences that it might have. It is not enough to just not intend to do the act.

Mental incompetence can be as a result of a mental illness, intellectual disability or impairment of the mind resulting from senility. Mental illness is defined in s 269A of the Criminal Law Consolidation Act 1935 and includes a temporary impairment of short duration.

A person’s mental competence will be presumed unless the Court finds that the person was not mentally competent to commit the offence or mentally competent to stand trial. A separate hearing will be held by the Court to decide mental competence. To rely on the mental impairment defence it is necessary to establish mental imcompetence on the balance of probabilities.