Capacity assessment sits at the heart of consent law in Canada because it determines whether a person can make their own treatment decisions. The legal authority to accept or refuse healthcare flows directly from the finding that a person possesses the requisite mental capacity to understand and appreciate the consequences of that decision. When capacity is present, the individual's choice must be respected regardless of whether others agree with it. When capacity is absent, decision-making shifts to a substitute decision-maker who must act in accordance with the person's prior expressed wishes or best interests. The stakes of getting this assessment wrong run in both directions. Treating a capable person without their consent constitutes battery at common law and violates their constitutional rights to security of the person and bodily autonomy. Conversely, accepting a refusal of treatment from a person who lacks capacity to make that decision may result in preventable harm or death. Professionals working in controlled care environments must understand both when capacity assessment is required and how it should be conducted to meet the legal standard that applies across Canadian jurisdictions.
The legal framework governing capacity assessment draws from multiple sources including provincial health care consent legislation, mental health statutes, health professions regulation, and common law principles that apply throughout Canada except where modified by Quebec's civil law system. In common law provinces, the test for capacity has been articulated through judicial decisions and subsequently codified in legislation such as Ontario's Health Care Consent Act, British Columbia's Health Care (Consent) and Care Facility (Admission) Act, Alberta's Personal Directives Act, and Saskatchewan's Health Care Directives and Substitute Health Care Decision Makers Act. While the specific language varies across jurisdictions, the core elements remain consistent. A person is capable with respect to a treatment decision if they can understand the information relevant to making the decision and appreciate the reasonably foreseeable consequences of making or not making that decision. This two-part test requires both cognitive understanding of the facts and the ability to apply that information to one's own situation. As of the date of authorship, these legislative frameworks maintain this fundamental approach while varying in procedural details regarding who may conduct assessments and what review mechanisms exist.