Ratio decidendi is a phrase derived from Latin, which means the reason or rationale for the decision. Primarily used in legal terminology, ratio decidendi refers to the rationale that a judge or court uses to support a decision or judgment in a court case. There may be legal, social, ethical, or moral principles underlying a court decision, and it is these principles that collectively form the ratio decidendi. For various reasons, it may be difficult to determine the ratio decidendi of a particular case, but the best way to do so is to read the court opinion carefully to discern the reasons for the ruling on the case.
Some helpful techniques for determining ratio decidendi include isolating the facts that are material, relevant to the court ruling, and identifying legal precedent that the court relied on in reaching its decision. Under common law principles, the applicable laws, as applied to the facts of a specific case, directly determine the correct outcome or holding of a case. Material facts and previous decisions of the courts often make up the rationale behind a ruling on a certain case. Like these previous decisions, the legal grounds for the court judgment generally are binding on courts when they make decisions in the future.
Identifying the holding of a case is important because it forms the basis for other court rulings. Being able to recognize the stated rationale of a court that supports a judgment is an essential legal skill taught almost universally to law students who are training to become lawyers. In the practice of law, lawyers can use the ratio decidendi of a case ruling to make arguments in similar cases in the future. Since courts typically must follow precedent or the rationales of previous case rulings, ratio decidendi of one case can be determinative of other cases with like facts or circumstances. Therefore, despite difficulties in doing so, discovering the holding of a court case is necessary.
Further complicating the analysis of a case ruling for its ratio decidendi is that the majority of court opinions contain extraneous information that may cloud the true rationale of the case. The court ruling may include facts that are not always pertinent to the main issues in the case and statements on the law that are not directly relevant to the main point of the ruling. This additional information can distract the reader from the main point of the court ruling and may confuse the point of law that the court is trying to make. Legal scholars call these additional fact orbiter dicta.