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Mental Capacity – The Law

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Mental capacity has always been something of a problem area of the law. The aim of the Mental Capacity Act 2005, which became fully operational in October 2007, is to put the administration of the various areas of law in which mental capacity is in point on a sounder legal footing.


The Act is based on the concepts of ‘best interests’ and ‘capacity’. Under the Act, capacity is stated to be absent when the person is unable ‘at the material time…to make a decision for himself in relation to the matter because of an impairment of, or disturbance in the functioning of, the mind or brain’. Interestingly, the lack of capacity need not be absolute or permanent – it can be limited in both time and to the matter which is under consideration. A person may lack capacity at one time and not another and may lack capacity with regard to some sorts of decisions and not others.


Capacity is considered to be lacking in a person if he or she:


  • cannot understand the information relevant to the decision, including the consequences which flow from making or failing to make it;
  • cannot retain the information long enough to make the decision;
  • cannot use the information as part of their decision-making process; or
  • cannot communicate their decision by any means.

 Once it is decided that a person lacks the mental capacity to make a decision, those responsible for making decisions on their behalf are required to do so in whatever way is in that person’s best interests.


A person is assumed to have capacity unless it can be established that he or she does not. Before that is decided to be the case, all practical steps must have been attempted without success to facilitate their making a decision.


The fact that a person lacks capacity does not mean that their wishes should be ignored. An attorney appointed to make decisions on their behalf should consider their current and past wishes, the views of relevant others (such as family members) and any beliefs or values that the person who lacks capacity might hold which would affect a decision.