Per incuriam

Per incuriam identifies a legal decision made in ignorance of a binding authority or a directly applicable statutory provision. The doctrine operates chiefly as a limited exception to the principle of stare decisis, under which courts generally follow applicable earlier decisions. English appellate courts have treated the exception cautiously because an expansive use of the label would weaken the predictability and hierarchical discipline of precedent.¹

The mistake must normally concern a proposition of law that the earlier court was bound to apply. A judgment is not per incuriam simply because the later court thinks the earlier court misunderstood the facts, adopted an unpersuasive interpretation, or failed to discuss every authority cited by the parties. The doctrine therefore addresses an exceptional defect in the decision-making process, rather than ordinary legal error.

In England and Wales, the leading statement is Young v Bristol Aeroplane Co Ltd, which set out the general rule that the Court of Appeal is bound by its own previous decisions subject to limited exceptions, including a decision given per incuriam.¹ The exception is intended to prevent an overlooked binding rule from becoming entrenched through repetition.

The Court of Appeal has also emphasized that the omission must be genuine and material. In Morelle v Wakeling, the court rejected an attempt to treat an earlier decision as per incuriam where the alleged oversight amounted, at most, to an arguable failure in reasoning rather than ignorance of a binding authority.² The doctrine is consequently narrower than the power to distinguish a precedent on its facts or to identify it as wrongly decided.

Per incuriam does not give every court a general licence to disregard higher authority. A lower court remains bound by a decision of a superior court even if it considers that decision mistaken; its usual options are to apply it, distinguish it, or invite appellate reconsideration. The Court of Appeal’s limited ability to depart from its own decisions must be read alongside the wider rules governing the Supreme Court and the former House of Lords.

The Practice Statement of 1966 authorized the House of Lords to depart from its previous decisions when appropriate, while warning that precedent remained an indispensable foundation of legal decision-making. Modern courts therefore distinguish per incuriam from ordinary overruling: the former concerns an overlooked controlling rule, whereas the latter is an authoritative decision that an earlier rule should no longer govern.

The doctrine can arise from overlooked legislation as well as overlooked case law. A court may also examine whether the supposed authority was truly binding: an observation made obiter, a decision from a nonbinding jurisdiction, or a materially different statutory regime will not ordinarily support a per incuriam argument. The question is one of legal status and materiality, not merely whether the earlier judgment was brief.

Its practical use is often defensive. Lawyers may argue that a later court should avoid mechanically applying a precedent that conflicts with an authoritative statutory rule, while opposing counsel may respond that the alleged omission was debated, immaterial, or compatible with the result. Because the label can affect the reliability of reported law, courts usually identify the precise overlooked authority and explain why it would have altered the legal analysis. The doctrine does not erase the earlier judgment from legal history or automatically invalidate orders already made.

Stare decisis

The principle that courts should follow applicable judicial precedents.

Ratio decidendi

The legal principle necessary to the decision, as distinct from incidental observations.

Obiter dictum

A judicial observation that is not necessary to the decision and is generally not binding.

Per incuriam

A decision made through oversight of a binding authority or applicable law.