Ratio vs obiter
Only part of a judgment binds later courts: the ratio decidendi — the reason for the decision, meaning the material facts plus the decision on them. Everything else is obiter dictum, "a saying by the way," which is persuasive but not binding. There is no mechanical test for extracting the ratio, and in a multi-judge court it may have to be distilled from several judgments by finding the common denominator the court agreed was essential.
Vertical vs horizontal precedent
The doctrine has two dimensions, and the difference is crucial:
- Vertical stare decisis is a binding rule: a lower court must follow the ratio of a superior court — the Circuit Court follows the High Court, Court of Appeal and Supreme Court, and so on. A lower court remains bound even if the superior court has hinted its decision may be wrong; it must wait for the superior court to overrule itself.
- Horizontal stare decisis is a policy, not an absolute rule: it asks whether a court is bound by its own past decisions. In The State (Quinn) v Ryan [1965] IR 70 Binding (IE) the Supreme Court held it is not absolutely bound by itself — stare decisis is "a policy and not a binding, unalterable rule" (Walsh J).
The threshold for a court to depart from itself is demanding. In Mogul of Ireland v Tipperary (NR) CC [1976] IR 260 the Supreme Court held it is not enough to prefer a different result; the later court must be clearly of opinion the earlier decision was erroneous. That high bar was met in The People (DPP) v JC [2017] 1 IR 417, which overruled DPP v Kenny as wrong in principle.
Escaping a precedent
Three distinct mechanisms loosen a precedent's grip — and confusing them loses marks:
- Distinguishing — a later court finds the material facts meaningfully different, so the precedent does not apply.
- Overruling — a superior court (or a court departing from itself) declares an earlier decision wrong for the future (e.g. JC overruling Kenny).
- Reversing — an appeal court changes the outcome of the same case on appeal.
A decision may also cease to bind if it was per incuriam — reached in ignorance of a relevant statute or authority (Brown v Donegal County Council [1980] IR 132) — though a court may only use this against equal or inferior courts, never a superior one.
The full, exam-ready version
Precedent and stare decisis: ratio vs obiter, the full hierarchy, the departure threshold (Quinn → Ryan's Car Hire → Mogul → JC), and every escape route — with a case table, decision-tree and model-answer skeleton. Checked against the primary sources.
or browse all modules →Frequently asked questions
What is the difference between ratio and obiter?
The ratio decidendi is the reason for the decision (material facts plus the decision on them) and it binds later courts. Obiter dicta are remarks "by the way" and are only persuasive.
Is the Supreme Court bound by its own decisions?
No — The State (Quinn) v Ryan [1965] held stare decisis is a policy, not an unalterable rule. But it will depart only where the earlier decision is clearly wrong (Mogul; applied in JC).
What is the difference between overruling and distinguishing?
Distinguishing avoids a precedent on materially different facts; overruling is a higher court (or a court departing from itself) declaring an earlier decision wrong for the future.