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The Mental Capacity Act 2005 provides a legal framework for assessing whether a person can make a specific decision about their care, finances, medical treatment, residence, or other personal matter. A capacity assessment is not a general judgment of someone’s intellect or competence; it is a practical, time-specific, decision-specific evaluation. Understanding how it is carried out and what should be recorded helps parents, carers, solicitors, and healthcare professionals ensure that the assessment is lawful, fair, and properly documented.
The five principles of the Mental Capacity Act
Before any capacity assessment takes place, the Mental Capacity Act 2005 establishes five core principles that guide the entire process. These apply to everyone—healthcare staff, social workers, solicitors, and family members—who must make decisions or assessments affecting someone who may lack capacity.
First, presume capacity: “A person must be assumed to have capacity unless it is established that he lacks capacity.” The burden of proof falls on the person asserting that capacity is absent; the starting point is always that the individual can decide for themselves.
Second, support decision-making: Before concluding someone lacks capacity, all practicable steps must be taken to help them make their own decision. This might include explaining information in simple language, using visual aids, involving someone they trust, choosing a better time when they are more alert, or finding an alternative form of communication.
Third, respect unwise decisions: Making an unwise or eccentric choice does not indicate lack of capacity. A person can decide something risky or contrary to medical advice. Capacity is about whether they understand and can weigh the information, not whether they choose wisely.
Fourth, act in best interests: If someone does lack capacity to make a decision, anyone acting on their behalf must do so in their best interests and consider their known wishes, beliefs, and values.
Fifth, use the least restrictive approach: Before restricting someone’s rights or making a decision for them, consider whether the aim could be achieved in a less restrictive way.
The two-stage test for lack of capacity
The Mental Capacity Act uses a two-stage functional test. Both stages must be satisfied to establish lack of capacity; satisfying only one is insufficient.
Stage 1: The impairment or disturbance test. The person must have an “impairment of, or a disturbance in the functioning of, the mind or brain.” This can result from illness, brain injury, dementia, mental health disorder, learning disability, the effects of drugs or alcohol, or physical illness affecting the brain. Importantly, whether the impairment is permanent or temporary makes no difference under the law. A temporary disturbance—delirium from an infection, intoxication, or medication side effect—can render someone incapable of making a decision at that moment, even if full capacity returns later.
Stage 2: The functional test. Because of that impairment or disturbance, the person is unable to make a decision about the specific matter in question. This is where the four functional elements come into play (see below).
The four functional elements
If Stage 1 is met, the assessment moves to Stage 2: can the person, as a result of their impairment, understand, retain, weigh, and communicate information about this decision? All four elements must be present for capacity; failure in any one means lack of capacity.
Understand: Can the person grasp the relevant information? Information should be provided in a form they can access—simple language, written and verbal, pictures, video, or whatever works. The person does not need to understand every detail or nuance; they must understand the material facts and the reasonably foreseeable consequences of deciding one way or another (or not deciding at all).
Retain: Can the person hold the information in mind long enough to make a decision? The law recognizes that retention can be brief; someone does not lack capacity simply because they forget information quickly, provided they can retain it for long enough to weigh it and make a choice.
Use or weigh: Can the person use or weigh the information as part of their decision-making process? This means comparing options, considering risks and benefits, and forming a reasoning based on their own values and wishes. Someone who cannot weigh information—because of confusion, denial, or cognitive impairment—lacks this element.
Communicate: Can the person communicate their decision by any means—speech, sign language, writing, pointing, blinking, or any other method that conveys their choice? A person who cannot communicate a decision, no matter how clear their thinking, fails this element.
The test is strictly decision-specific and time-specific. Someone may have capacity to decide where to live but lack capacity to manage complex finances. A person who lacks capacity today may regain it once treatment for delirium or depression takes effect. Capacity can fluctuate.
Recording a capacity assessment
A formal written record is essential, both for legal protection and for continuity of care. The record should be made contemporaneously—immediately after the assessment—and should document:
- Who was assessed and when: Date, time, and the specific decision in question.
- Who carried out the assessment: Their name, role, and qualifications.
- The information provided: What was explained to the person and in what form (verbal, written, visual aids, etc.).
- Evidence of support: What steps were taken to help the person make their own decision.
- The person’s responses: What the person said and did during the assessment; any communication difficulties or behaviour noted.
- The conclusion: Whether the person has capacity or lacks capacity.
- If lacking capacity, the reasoning: Which stage or functional element failed and why, with specific examples.
- Any actions taken: What decision was made, by whom, and on what basis (e.g., best interests).
Many healthcare settings and local authorities use standardized capacity assessment forms to ensure consistency and clarity. The form should be clear enough that a court or another professional could read it and understand the reasoning. Vague statements like “patient lacks capacity” without supporting detail are of little value.
When a formal assessment or report is needed
Not every capacity assessment requires a psychiatrist or formal report. Healthcare staff, social workers, and family members routinely assess capacity in everyday situations. A formal assessment by a mental health professional becomes necessary when:
- Capacity is genuinely unclear or disputed.
- The person’s presentation is complex—for example, they have dementia plus mental illness plus a recent physical illness.
- The decision is high-stakes—medical treatment, major financial matter, residence, or child-related decisions.
- The assessment will be disclosed to court or used in legal proceedings.
- A third party (a solicitor or local authority) has commissioned the assessment as part of litigation or formal safeguarding.
In such cases, an expert assessment by a psychiatrist or psychologist trained in capacity work, documented in a formal report that explains the functional test step-by-step, provides a thorough record and an independent professional opinion.
The causative nexus
A key principle, often called the “causative nexus,” requires that the inability to make the decision must be caused by the impairment. It is not enough to show that someone has an impairment and also happens to make an unwise decision. The link between the impairment and the inability to decide must be demonstrated. For example, if someone with mild depression makes a risky financial choice, the assessment must show how the depression (not just prudential judgment) has impaired their ability to understand, retain, weigh, or communicate about finances. This focus on causation prevents misuse of capacity assessment to override people’s autonomous choices simply because others disagree with them.
Key points
- Capacity is presumed; the burden of proof falls on those claiming it is absent.
- The test is functional, decision-specific, and time-specific—not a global judgment of intelligence.
- Stage 1 requires an impairment or disturbance of mind or brain (permanent or temporary).
- Stage 2 requires failure in understanding, retention, weighing, or communication of information about that specific decision.
- Support and alternatives must be explored before concluding capacity is absent.
- A written record documenting the assessment, the evidence, and the reasoning is essential for both protection and clarity.
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