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Legal capacity has two components – age and decisional capacity.


The age component of legal capacity is determined by legislation – ie, the age at which the law confers certain rights and obligations on individuals at different stages in their lives.

The age of full legal capacity in South Africa is 18.1 In terms of consent to clinical treatment, this means that people of 18 and older should be assumed to have the decisional capacity to make choices on their own behalf, unless there is good reason to believe that they have a mental impairment that compromises their ability to make specific decisions.

Children of 12 or older who have the maturity to understand the implications of a proposed treatment may consent on their own behalf. If a surgical procedure is being proposed, the child's consent must be accompanied by a parent or guardian's written assent (see "Children and young people" for more information).2 There are other circumscribed situations (for example, HIV testing or termination of pregnancy) in which the law sets out who may give consent, depending on the circumstances. These are covered later in this booklet.

Decisional capacity

There are two overriding principles to bear in mind regarding a person’s capacity to consent to treatment:

  • Adults are presumed to be competent to make decisions. You must therefore be satisfied that they lack the capacity to make a particular decision before intervening without their consent.
  • Minors are generally presumed to lack decisional capacity. You must therefore be satisfied that they have the capacity (maturity) to make a particular decision before intervening with their consent.

Decisional capacity (also referred to as “mental capacity”) is variously defined as the capacity to make decisions in light of information about the relevant risks, benefits and consequences of the proposed intervention, specifically being able to:

  • Understand relevant information
  • Appreciate the consequences of the situation
  • Reason about treatment.3

Decisional capacity is not an “all or nothing” concept. A patient might, for example, be perfectly capable of grasping the implications of minor surgery to remove a sebaceous cyst, but be unable to comprehend all the risks and benefits associated with a bowel resection. The capacity to consent to treatment is, therefore, decision-specific.

A patient’s decisional capacity might also fluctuate over time – even in the course of a day – so the time at which consent is sought may be crucial.

Box 1: Defining incapacity

The following extract is from a proposed Bill. It has not been tabled in Parliament yet, and is unlikely to be in the near future, but the principles it contains can nevertheless be followed as a matter of good practice.

Adult with incapacity

4. (1) An adult is an adult with incapacity if at the time a decision needs to be made he or she is unable, temporarily or permanently and irrespective of the cause – (a) to make the decision for him or herself on the matter in question; or (b) to communicate his or her decision on that matter.

4. (2) An adult is unable to make a decision for him or herself as contemplated in subsection (1a) if he or she is unable (a) to understand or retain the information relevant to the decision; or (b) to make an informed, rational decision based on that information.

4. (3) An adult must not be regarded as unable to understand the information referred to in subsection (2a) if he or she is able to understand an explanation of the information in broad terms and in simple language.

4. (4) An adult must not be regarded as unable to make a decision referred to in subsection (2b) merely because he or she makes a decision which would not be made by a person of ordinary prudence.

4. (5) An adult must not be regarded as unable to communicate his or her decision referred to in subsection (1)(b) unless all practicable steps to enable communication of the decision has been taken without success.

Source: South African Law Reform Commission, Discussion Paper 105, Assisted Decision-making: Adults with Impaired Decision-making Capacity (January 2004).