Latin (plural rationes decidendi)) for “reasons or rationale for the decision.” In other words, it is the legal principle or rationale on which a decision (e.g., judicial) is based and issued. It constitutes a key factual point or chain of reasoning, in a case, on which the final judgment or verdict is determined. The ratio decidendi of a case does not constitute the actual decision, order, or judgment.

The ratio decidendi establishes a precedent, which is the legal principle used by the court in issuing a verdict on the legal case defined by the available facts. This legal principle is an abstraction from such facts in the context of the proceedings. A court may use earlier cases as precedent, stipulating that the parties to the case clearly interpret the ratio decidendi of the earlier case.