Capacity and competence are terms that are often used interchangeably. Capacity is a functional term that refers to the mental or cognitive ability to understand the nature and effects of one's acts . Competence is a legal term that can be defined as being "duly qualified: having sufficient, capacity, ability or authority" — in practice it requires health professionals to perform a functional test of competence to examine the ability of the particular patient to consent to the specific treatment being offered