Definition reprinted with permission from Committee on Psychiatry and Law, of the Group for the Advancement of Psychiatry: Mental Health Professional and the Legal System
The legal requirement that there be some competent evidence before a person can be detained. For a criminal arrest, some evidence must exist establishing that a crime has been committed and that the person being arrested was involved. In civil commitment, probable cause normally requires some evidence of mental illness and harmfulness. Probable cause does not mean proof; it means only that there is a rational basis to allege and retain an individual.