Whether or not a person has capacity is a determination made by the Court. It is a legal concept and the definition varies by jurisdiction. A doctor’s opinion on capacity remains an opinion until a judicial ruling on the evidence is given. All adults are presumed to be competent until proven otherwise.
Under current Michigan law, an “incapacitated person” is defined as an individual who is impaired by reason of mental illness, mental deficiency, physical illness or disability, chronic use of drugs, chronic intoxication, or other cause, to the extent of lacking sufficient understanding or capacity to make or communicate informed decisions. MCL 700.1105(a). If a person (other than a minor) is determined by a Court to be legally incapacitated, then a guardian is appointed to provide continuing care and supervision for that individual.
The law recognizes that a person is rarely totally incapacitated. Capacity may depend on the type of decision that needs to be made or the surrounding circumstances. For instance, a person may be capable of handling personal safety issues but not money matters. Often the Court will consider appointment of a limited guardian that is only allowed to assist the incapacitated individual under specific circumstances.