Assessing capacity means determining whether a person can understand, process, and communicate a specific decision at a specific point in time. It is not a general judgment about someone’s intelligence or mental health. Instead, it focuses on four core abilities: understanding relevant information, appreciating how that information applies to their situation, reasoning through the options, and expressing a choice. If a person can demonstrate all four, they have capacity for that decision, regardless of whether others agree with what they choose.
The Four Abilities You’re Testing
Every capacity assessment comes down to four questions. These form the accepted clinical standard across most jurisdictions, and tools like the MacArthur Competence Assessment Tool for Treatment (MacCAT-T) are built around them.
- Understanding: Can the person grasp the key facts about their situation, including what’s being proposed, what the risks and benefits are, and what alternatives exist? This isn’t about memorizing medical jargon. It’s about whether they can take in the information when it’s explained in plain terms and repeat it back in their own words.
- Appreciation: Can the person recognize how this information applies to them personally? Someone might understand what surgery involves in the abstract but deny they have the condition that requires it. That gap between understanding the facts and connecting them to their own life is what appreciation captures.
- Reasoning: Can the person weigh the options? This means comparing potential outcomes, considering what matters to them, and thinking through consequences. You’re not looking for a “correct” answer. You’re looking for a logical process, even if their values lead them to a choice you wouldn’t make.
- Communicating a choice: Can the person clearly state what they want? This doesn’t require verbal speech. Writing, gesturing, or using assistive devices all count. The key is consistency: a person who gives a different answer every few minutes may not be able to reliably communicate a decision.
A structured interview using the MacCAT-T takes roughly 15 to 20 minutes. The clinician first gathers the relevant clinical details, then walks through a semi-structured conversation tailored to that specific patient and decision, and finally scores each of the four domains. It’s individualized, not a generic questionnaire.
Capacity Is Decision-Specific
One of the most commonly misunderstood aspects of capacity is that it applies to a particular decision, not to a person as a whole. Someone can have the capacity to agree to a blood draw but lack the capacity to consent to a complex surgical procedure. The threshold rises with the stakes. This is sometimes called the “sliding scale” concept: more stringent requirements apply to more consequential decisions.
This means you cannot label someone as globally “lacking capacity” based on a single assessment. Each new decision, especially one with different risks or complexity, requires its own evaluation. A person with mild dementia might manage everyday choices perfectly well while struggling with decisions that involve weighing multiple long-term outcomes.
Capacity vs. Competence
These terms get used interchangeably, but they mean different things. Capacity is a clinical determination made by a treating physician or other qualified health professional. Competence is a legal status that only a court can grant or remove. A clinician can document that a patient lacks the clinical capacity to make a specific healthcare decision, but that finding doesn’t strip the person of their legal rights. People remain legally competent until a judge declares otherwise through a guardianship or conservatorship proceeding.
This distinction matters in practice. If a physician determines a patient lacks clinical capacity but the patient objects to that finding, the physician often cannot simply override the patient’s stated preference. The courts get involved when the clinical determination is challenged, or when decisions about finances, property, or long-term care arrangements are at stake.
When Capacity Fluctuates
Capacity is not always stable. It can shift with the time of day, medication effects, pain levels, infections, or emotional state. Delirium is a common cause of fluctuating capacity, particularly in older adults. It involves sudden changes in attention, awareness, and thinking that tend to come and go over the course of a day.
When someone’s capacity fluctuates, the assessment should be timed carefully. If a person with delirium has lucid intervals where their thinking clears, those windows may be the right moment to have a conversation about their care preferences. The Confusion Assessment Method (CAM) can help identify whether delirium is present by looking for acute onset, fluctuating course, inattention, and disorganized thinking. Ongoing reassessment is essential rather than relying on a single snapshot.
If a decision can wait until the person regains capacity, it should. This is a core principle: the least restrictive option always takes priority. Temporary impairment from anesthesia, an infection, or a medication side effect does not justify permanent decisions about someone’s autonomy.
How to Structure the Assessment
Start by identifying the specific decision that needs to be made. Then provide the person with all the relevant information in language they can understand, adapting for hearing loss, language barriers, learning disabilities, or anxiety. The assessment itself is a conversation, not a test. You’re creating the best possible conditions for the person to demonstrate their abilities.
Walk through each of the four domains in order. Ask the person to explain back what they understand about their condition and the proposed treatment. Ask them what they think will happen if they agree or refuse. Ask how they arrived at their preference. Listen for whether their reasoning connects logically, even if it reflects values different from your own. A person who refuses a blood transfusion on religious grounds is not lacking capacity. They are weighing the decision through a framework that matters to them.
The UK Supreme Court has clarified a useful sequence for the overall process. First, determine whether the person can make the decision in question at the time it needs to be made. If they cannot, identify whether there is an impairment or disturbance in the functioning of their mind or brain. Then establish whether that impairment is the reason they cannot make the decision. This sequence prevents the common mistake of assuming that a diagnosis alone (dementia, psychosis, brain injury) equals incapacity. The diagnosis must be the cause of the inability, not just present alongside it.
Documenting Your Findings
Good documentation protects the patient and the assessor. Record the specific decision being assessed, not just “capacity assessment performed.” Note when the assessment took place, since timing matters for someone whose abilities fluctuate. Describe the information you provided to the patient and how you adapted it for their needs.
For each of the four domains, document what the person said or did that demonstrated their ability or inability. Use their own words where possible. If you determine the person lacks capacity, record the specific impairment and explain how it connects to their inability to meet the threshold. If the person later regains capacity, document that too. A finding of incapacity is not permanent unless the underlying condition is.
What Happens When Someone Lacks Capacity
When a person cannot make a particular decision, someone else must make it on their behalf, and that decision must be made in the person’s best interests. The “decision-maker” is typically whoever is responsible for the relevant area of care: a doctor for treatment decisions, a social worker for care arrangements, or a family carer for everyday matters.
Best interests is not simply what the decision-maker thinks is medically optimal. It requires considering the person’s past and present wishes, their values and beliefs, and any preferences they expressed when they did have capacity. The person should still be involved as much as possible. Consulting family members, friends, and anyone else who knows the person well is part of the process.
A practical approach for difficult decisions is the “balance sheet” method: listing the benefits and burdens of each option side by side, weighted by what matters to the individual rather than by clinical convention alone. Assumptions based on someone’s age, appearance, diagnosis, or behavior are explicitly prohibited. A person with severe physical disabilities, for example, may place a very different value on quality of life than an outside observer would predict.