Sui juris is a legal term referring to someone who has full legal capacity for making decisions and engaging in legal activities. The person is not subject to the authority of anyone else and is deemed competent to manage personal legal affairs. Generally, all people over the age of majority are considered sui juris unless there are compelling reasons to believe otherwise. Taking legal rights from adults requires a review process to prove their incapability and appoint a guardian to act on their behalf.
This term literally translates as “own law,” referencing the idea that people can legally act on their own. Historically, minor children have not been considered sui juris, with the age of majority varying depending on the time and the region. They are not held responsible for certain legal actions and are under the supervision of their parents. While it is possible for juveniles to face legal penalties for breaking the law, the court system treats them differently. People can also make decisions on behalf of minors and compel them to abide by those decisions.
Mentally incompetent individuals, generally including people with severe intellectual disabilities, are also not sui juris. Courts may also temporarily suspend legal rights in the case of a person with mental illness who is posing a danger, with the understanding that after treatment, the patient's legal independence will be restored. Guardians appointed in such cases are expected to act in the interests of their wards and to request a change in legal status if a ward appears capable of understanding and making legal decisions.
In some nations and at various points in history, certain other classes of people have also been stripped of their legal rights. People in bankruptcy, for example, have not always been considered sui juris. Such individuals were subject to rulings from the court and were expected to make good on their legal rights before they could be legally independent. Likewise, historically some nations restricted full legal rights to male landowners, while other members of the population were not sui juris.
People acting with sui juris are expected to understand and comply with the law. They can engage in legal decisions and will be familiar with the consequences of violating contracts or failing to obey the law. In special situations, people may argue that they are not liable for a crime due to temporary insanity, a state that interfered with their ability to understand the consequences of their actions. The “insanity defense,” as it is known, can be difficult to prove.