Decision-making capacity: the four abilities

Capacity isn't a verdict on the person — it's whether, for this decision, right now, they can do four specific things.

The idea

Capacity is presumed until there's reason to doubt it, and it's assessed against a functional model, not a diagnosis. A patient has capacity for a decision when they can do four things: understand the relevant information, appreciate that it applies to them, reason with it to weigh the options, and express a choice.

Two properties change everything. Capacity is decision-specific and the bar scales with the stakes — the same person can have capacity to pick a meal but need a clearer demonstration of reasoning to refuse a life-saving treatment. And it can fluctuate, so when you assess matters as much as how.

Vignette. Mr. Alvarez, 68, is deciding about a recommended procedure. He is lucid right now. Ask probing questions to see which abilities he can demonstrate — the dials fill only when a question actually establishes that ability.

Ask a probing question

Stakes of the decision: a moderate decision — higher stakes raise the bar the dials must clear

an elective procedure with real but recoverable risk

Capacity is presumed. Ask questions to establish each of the four abilities for this decision.

Pick an open probe above. Notice that closed or leading questions don't fill a dial — a nod isn't evidence.

How it works

Assess each ability functionally, then read all four against a bar set by the stakes:

the four abilities (assess against THIS decision):
    understand   restate the situation, options, risks, benefits
    appreciate   grasp that it applies to ME, not in the abstract
    reason       compare options against my own values and goals
    express      communicate a stable, consistent choice

has capacity  =  clears the bar on ALL FOUR
bar height    scales with stakes  (low-risk choice -> lower bar,
                                    grave, hard-to-reverse -> higher bar)

capacity is:  decision-specific . fluctuating . presumed until shown
              otherwise . distinct from legal competence

Capacity vs competence. Capacity is a clinical judgment about a specific decision at a specific time. Competence is a legal status determined by a court. A clinician assesses the former; only a court rules on the latter.

When to use it

Situation	How the model guides you
A patient refuses a recommended treatment	Assess capacity for that decision — a refusal isn't itself evidence of incapacity
Fluctuating states (delirium, intoxication, post-op)	Time the assessment to a lucid interval; reassess rather than deciding once
High-stakes, hard-to-reverse choice	Demand a clearer demonstration of reasoning; document it carefully
Trade-off	It's a judgment, not a score; two skilled assessors can disagree at the margin

Watch out for

Confusing an unwise choice with incapacity. A patient may refuse what you'd choose and still have full capacity. Rate the four abilities, not the answer.
Judging the whole person. Capacity is decision-specific. Someone can lack it for a complex financial choice yet retain it for a simple medical one.
Assessing at the wrong moment. A single snapshot during delirium or peak pain misses a lucid interval. Capacity fluctuates; so should your reassessment.
Mistaking a signature or a nod for understanding. “Understand” means they can restate it. Ask open questions and listen for their words, not yours.
Applying one fixed bar. The threshold should scale with the consequences — but “higher stakes” means probe and document more, never override a capacity the patient actually demonstrates.

Worked example

An interviewer says: “A post-op patient, still drowsy, waves off your explanation and refuses further treatment. Walk me through your assessment.” A strong answer resists a snap verdict. You'd note capacity is presumed but this is a fluctuating state, so you time the assessment to a lucid window. Then you probe each ability functionally — can he restate the plan, appreciate that it's his situation, reason through the alternatives, and voice a stable choice? Because refusing treatment is high-stakes, you hold reasoning to a clearer bar and document it — and if he clears all four, you respect the refusal rather than treating incapacity as the convenient conclusion.

Check yourself

A patient understands his diagnosis and options and voices a clear choice, but insists the cancer “isn't really mine — the scans got mixed up,” against clear evidence. Which ability is in question?