This may be discussed taking into consideration:

• Overruling a Precedent
• Refusal to Follow a Precedent
• Impugning a Precedent
• Abrogated Decisions
• Decisions of Equally Divided Courts
• Incorrect Decisions

Overruling a Precedent

If a precedent is overruled, it becomes null and void, and is deprived of all its authority. It is substituted by a new principle. Only a superior jurisdiction can overrule a precedent.

Refusal to Follow a Precedent

The act of refusing to follow a precedent is an act of co-ordinate jurisdiction. Two courts of equal authority are under no obligation to follow precedents established by each other. They do not have the authority to overrule the other’s precedents but hey can refuse to follow them. When this happens, the two conflicting decisions have to wait for a Court superior to both of them to resolve the conflict by choosing to apply one of the precedents.

Impugning a Precedent

If a point of law has not been argued at all or a precedent has been passed sub silentio, no precedent is created in regard to it. However, if a point is badly argued, the inadequacy of the precedent is a ground for having an authoritative and binding precedent impugned.

Abrogated Decisions

Abrogated Decisions include:
1. Decisions which have been overruled or reversed by a higher Court
2. Decisions which lose their authority because a statute which conflicts with them is enacted later.

It is not entirely clear what happens when a decision is overruled or reversed on a point other than that on which it had been previously decided, although the general view appears to be that the point which the later judgment does not speak of is not overruled or reversed but that it loses some of its authority as a precedent.

Decisions of Equally Divided Courts

Courts are rarely, if ever, equally divided – the general practice is for a Court to sit with an uneven number of members. However, an appeal is usually dismissed if the Appellate Court is equally divided following the maxim omnia praesumitur pro negante.

Incorrect Decisions

Decisions which are incorrect may be based on an incorrect understanding of the principles of law. Logically, they should not be binding but they may be allowed to stand on practical considerations if they have stood the test of time.

Court practice varies considerably. It appears that if people have entered into contracts relying on an incorrect decision, or if the decision affects proprietary rights, the courts will not overrule it although they are likely to overrule a decision which does such things as affect citizens’ rights.

Reference: Salmond on Jurisprudence