“There is at least one exception to the rule of stare decisis. I refer to judgments rendered per incuriam. A judgment per incuriam is one which has been rendered inadvertently. Two examples come to mind: first, where the judge has forgotten to take account of a previous decision to which the doctrine of stare decisis applies. For all the care with which attorneys and judges may comb the case law, errare humanum est, and sometimes a judgment which clarifies a point to be settled is somehow not indexed, and is forgotten. It is in cases such as these that a judgment rendered in contradiction to a previous judgment that should have been considered binding, and in ignorance of that judgment, with no mention of it, must be deemed rendered per incuriam; thus, it has no authority…. The same applies to judgments rendered in ignorance of legislation of which they should have taken account. For a judgment to be deemed per incuriam, that judgment must show that the legislation was not invoked.” Louis-Philippe Pigeon, Drafting and Interpreting Legislation 60 (1988).
“As a general rule the only cases in which decisions should be held to have been given per incuriam are those of decisions given in ignorance or forgetfulness of some inconsistent statutory provision or of some authority binding on the court concerned, so that in such cases some features of the decision or some step in the reasoning on which it is based is found on that account to be demonstrably wrong. This definition is not necessarily exhaustive, but cases not strictly within it which can properly be held to have been decided per incuriam, must in our judgment, consistently with the stare decisis rule which is an essential part of our law, be of the rarest occurrence.” Rupert Cross & J.W. Harris, Precedent in English Law 149 (4th ed. 1991).
