Mental Health Act 1959

4 Definition and classification of mental disorder

(1) In this Act " mental disorder " means mental illness, arrested or incomplete development of mind, psychopathic disorder, and any other disorder or disability of mind; and " mentally disordered " shall be construed accordingly.

(2) In this Act "severe subnormality" means a state of arrested or incomplete development of mind which includes subnormality of intelligence and is of such a nature or degree that the patient is incapable of living an independent life or of guarding himself against serious exploitation, or will be so incapable when of an age to do so.

(3) In this Act " subnormality " means a state of arrested or incomplete development of mind (not amounting to severe sub-normality) which includes subnormality of intelligence and is of a nature or degree which requires or is susceptible to medical treatment or other special care or training of the patient.

(4) In this Act " psychopathic disorder " means a persistent disorder or disability of mind (whether or not including sub-normality of intelligence) which results in abnormally aggressive or seriously irresponsible conduct on the part of the patient, and requires or is susceptible to medical treatment.

(5) Nothing in this section shall be construed as implying that a person may be dealt with under this Act as suffering from mental disorder, or from any form of mental disorder described in this section, by reason only of promiscuity or other immoral conduct.