Capacity is a clinical determination, one that physicians make, that addresses the integrity of mental functions. Competency is a legal determination that addresses societal interest in restricting a person’s right to make decisions or perform acts because of incapacity. The determination capacity of an adult patient will conclude that the patient has the ability to understand medical conditions and options for medical care.
The ability (capacity) to make decisions can be compromised by illness, medication, or other brain disease. This may determine when a health care agent or proxy is needed to make decisions.