Ratio Decidendi

Definition

Ratio decidendi ("the reason for deciding") is the legal principle or reasoning that forms the basis for a court's decision. It is the essential rationale that, combined with the material facts, leads to the court's holding. Only the ratio decidendi of a case is binding on future courts — obiter dicta and broader statements of policy are not. Identifying the ratio decidendi requires careful analysis of which facts the court deemed material and what rule the court applied to reach its conclusion.

Example

The ratio decidendi of Donoghue v. Stevenson is that manufacturers owe a duty of care to the ultimate consumer of their products. This reasoning became binding precedent.