What is mental capacity?

Mental capacity is the ability of a person to make decisions. The Mental Capacity Act 2005 was passed by Parliament to protect the rights and dignity of vulnerable adults. Prior to that time, the common law was relied upon, with some court rulings deemed controversial.

Vulnerable individuals include those with learning disabilities, mental health issues, disorders of the brain due to infections and injuries, and people with dementia.

The Mental Capacity Act requires that certain criteria be fulfilled before a person is deemed as lacking capacity. These criteria include ensuring that the person being assessed is supported to make the decision in question. For example, if a person is hard of hearing, communication needs to be optimised.

The actual test of mental capacity as set out in the Mental Capacity Act requires that the person being assessed can understand, retain, weigh up and communicate the decision being assessed. In addition to these criteria, there has to be evidence of a disorder of the mind or brain causing the lack of capacity.

Mental capacity is decision and time specific which means that a person may have capacity for one decision but not for others. Mental capacity can even fluctuate on the same day. For example, people living with dementia often experience ‘sundowning’ which means they become more confused in the late afternoons and evenings. Undertaking a mental capacity assessment when an individual is experiencing 'sundowning’ is thus not appropriate as the Mental Capacity Act requires that individuals be supported when making the relevant decision.

Mental capacity may or may not return depending on the cause.