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Capacity vs Competence in Medicine: The Difference, With Examples
In US usage, capacity is a clinician's judgment about whether a patient can make a specific decision at a specific time. Competence is a legal status, and only a judge can rule that a person is legally incompetent and appoint a guardian (Vermont Ethics Network). Clinicians assess capacity with four abilities: communicating a choice, understanding, appreciating and reasoning (Stanford Encyclopedia of Philosophy).
In Britain the terms work differently: there, “capacity” is usually the legal term, and the Mental Capacity Act 2005 sets its own criteria for England and Wales (SEP, read October 31, 2026).
Capacity vs competence at a glance
| Capacity | Competence | |
|---|---|---|
| What it is | Capacity: A clinical judgment about one decision | Competence: A legal status about a person's authority to decide |
| Who decides | Capacity: The treating clinician | Competence: A judge |
| Scope | Capacity: Decision-specific, and can change over time | Competence: Authority over medical care, finances and other personal choices |
| Starting point | Capacity: Adults are presumed to have it | Competence: Only a judge can rule a person legally incompetent |
| If it is missing | Capacity: A surrogate decides this question | Competence: A court appoints a guardian |
The line is less clean in practice. The Stanford Encyclopedia notes that the usual split, a clinician determines capacity and a judge determines competence, “breaks down in practice,” because a clinician's capacity call often carries the weight of a legal judgment (SEP).
The four abilities clinicians assess
The most influential model, from Grisso and Appelbaum (1998), rests on four abilities, and the most widely used assessment tool, the MacCAT-T, is built on it (SEP). The questions are examples we wrote to show what each one sounds like at the bedside.
| Ability | How a clinician might check it |
|---|---|
| Communicate a choice | How a clinician might check it: "What have you decided about the surgery?" Can they state a choice and keep to it? |
| Understand | How a clinician might check it: "Can you tell me in your own words what the doctor recommended and why?" |
| Appreciate | How a clinician might check it: "What do you think will happen to you if you don't have it?" Do they see it applies to them? |
| Reason | How a clinician might check it: "How did you weigh the risks against the benefits?" Is the choice tied to their own values? |
Decision-specific, and on a sliding scale
- Presumed. All adults are presumed to have decision-making capacity, regardless of diagnosis (Vermont Ethics Network).
- Decision-specific. Capacity should be assessed relative to a specific decision, at a particular time, in a particular context (SEP).
- Changeable. Sleep, illness and medications all affect it, so a patient can have capacity some of the time.
- Sliding scale. Simple, low-risk decisions need less capacity. Complex decisions or ones with grave consequences need more (Vermont Ethics Network).
- Disagreement is not incapacity. A refusal the team dislikes is not evidence of incapacity by itself. What matters is the four abilities (our summary).
Capacity is also the gate to consent. Only adults with decision-making capacity can give informed consent.
When a patient lacks capacity
The AMA Code asks physicians to identify a surrogate: first anyone the patient named through a durable power of attorney for health care, otherwise a family member or other intimate associate in keeping with law and policy. It also asks physicians to involve the patient as far as their capacity allows (AMA Code). The AMA recommends advance care planning for everyone, regardless of age or health, partly so people can name who would decide for them (AMA Code). Resuscitation is the decision that most often comes up this way: see DNR vs DNI vs full code.
Capacity examples
| Case | How to read it |
|---|---|
| A man with mild dementia chooses between two blood pressure pills. | How to read it: Likely has capacity for this low-risk choice even if he lacks it for complex financial decisions. |
| A woman with delirium after surgery refuses a CT scan at 3 a.m. and is lucid by noon. | How to read it: Capacity changes over time. Reassess when the delirium clears, unless it is an emergency. |
| A capable adult refuses chemotherapy because she prefers time at home. | How to read it: Disagreeing with the team is not lack of capacity. Her reasons fit her values. |
| A patient under court guardianship asks to stop a medication. | How to read it: If the guardianship covers medical decisions, the guardian decides, but he should still be involved as far as he can be. |
In interviews, capacity sits inside refusal, consent and family-conflict stations. See ethical dilemmas in medicine and MMI ethics questions for more to practice on, and try the question-bank scenario of a pregnant patient with Down syndrome.
Practice question: a son wants to sign for his mother
The mistake most answers make
Treating the dementia diagnosis as the answer. The station is testing whether you know that capacity is about this decision, and that a capable patient's refusal stands even when the family disagrees.
“An 82-year-old patient with early dementia refuses a hip operation that her doctors recommend. Her son says she is confused and asks to sign the consent form for her. What do you do?”
A capacity station. A strong answer separates a diagnosis from capacity, checks this decision specifically, and knows who decides if she cannot.
Example answer written by Confetto (the applicant is invented)
First, a dementia diagnosis does not by itself mean she lacks capacity. Capacity is about this decision, at this time, so the question is whether she can make this particular choice.
I would ask the team to assess it properly. Can she tell us her choice and stay with it? Can she explain in her own words what the operation is for, what happens if she does not have it, and why she is refusing? If her reason is that she is afraid of never walking again after surgery, that is a real, values-based reason, even if the team disagrees.
If she has capacity, her refusal stands. We would make sure she has the information she wants, address her fears, and check she can change her mind. I would also talk with her son, because his worry is real, and explain that we cannot sign for her while she can decide for herself.
If she lacks capacity for this decision, the son or another surrogate would decide based on what she would have wanted, and she should still be involved as much as she can be. If the family disagreed or there was any doubt, I would ask for an ethics consult. Either way, a son signing for a capable mother is not an option.
Sources: the Stanford Encyclopedia of Philosophy, the Vermont Ethics Network and the AMA Code of Medical Ethics, linked throughout and checked October 31, 2026.
Frequently asked questions
What is the difference between capacity and competence?
In US usage, capacity is a clinical judgment about whether a patient can make a specific decision, and competence is a legal term for a person's authority to make their own decisions. Only a judge can rule that someone is incompetent. In Britain, capacity is usually the legal term. See the Vermont Ethics Network.
What are the four elements of decision-making capacity?
The ability to communicate a choice, to understand the information, to appreciate how it applies to you and to reason about the options. This is Grisso and Appelbaum's model, the most influential theory of competence, and the basis of the MacCAT-T, the most widely used assessment tool. See the Stanford Encyclopedia of Philosophy.
Who determines decision-making capacity?
The treating clinician, for the decision at hand. Adults are presumed to have capacity regardless of diagnosis, and higher-risk decisions call for a higher level of capacity.
What happens if a patient lacks capacity?
The AMA Code says the physician should identify a surrogate, starting with anyone the patient named through a durable power of attorney for health care, and still involve the patient as much as possible. Read the AMA opinion.
Can a patient with dementia have capacity?
Yes, for some decisions. Capacity is decision-specific and can change over time, so a diagnosis alone does not settle it.