Legal Dictionary

ratio decidendi

Legal Definition of ratio decidendi

Related terms

Definition of ratio decidendi


    Latin ratio (“reckoning, method, reasoning”) + decidendi, genitive singular of decidendus, gerund of decidere (“to settle”)


ratio decidendi (plural rationes decidendi)

  1. (law) The legal principle or rationale on which a judicial decision is based.

Further reading

Ratio decidendi (Latin plural rationes decidendi) is a Latin phrase meaning "the reason" or "the rationale for the decision." The ratio decidendi is "[t]he point in a case which determines the judgment" or "the principle which the case establishes."

In other words, ratio decidendi - legal rule derived from, and consistent with, those parts of legal reasoning within a judgement on which the outcome of the case depends.

It is a legal phrase which refers to the legal, moral, political, and social principles used by a court to compose the rationale of a particular judgment. Unlike obiter dicta, the ratio decidendi is, as a general rule, binding on courts of lower and later jurisdiction - through the doctrine of stare decisis. Certain courts are able to overrule decisions of a court of co-ordinate jurisdiction - however out of interests of judicial comity they generally try to follow co-ordinate rationes.

The process of determining the ratio decidendi is a correctly thought analysis of what the court actually decided - essentially, based on the legal points about which the parties in the case actually fought. All other statements about the law in the text of a court opinion - all pronouncements that do not form a part of the court's rulings on the issues actually decided in that particular case (whether they are correct statements of law or not) - are obiter dicta, and are not rules for which that particular case stands.


The ratio decidendi is one of the most powerful tools available to a lawyer. With a proper understanding of the ratio of a precedent, the advocate can in effect force a lower court to come to a decision which that court may otherwise be unwilling to make, considering the facts of the case.

The search for the ratio of a case is a process of elucidation; one searches the judgment for the abstract principles of law which have led to the decision and which have been applied to the facts before the court. As an example, the ratio in Donoghue v. Stevenson would be that a person owes a duty of care to those who he can reasonably foresee will be affected by his actions.

All decisions are, in the common law system, decisions on the law as applied to the facts of the case. Academic or theoretical points of law are not usually determined. Occasionally, a court is faced with an issue of such overwhelming public importance that the court will pronounce upon it without deciding it. Such a pronouncement will not amount to a binding precedent, but is instead called an obiter dictum.

Ratio decidendi also involves the holding of a particular case, thereby allowing future cases to build upon such cases by citing precedent. However, not all holdings are given equal merit; factors that can strengthen or weaken the strength of the holding include:

  • Rank of the court (Supreme Court versus an appellate court).
  • Number of issues decided in the case (multiple issues may result in so called, multi-legged holdings)
  • Authority or respect of the judge(s)
  • Number of concurring and dissenting judges
  • New applicable statutes
  • Similarity of the environment as opposed to the age of the holding.

The ability to isolate the abstract principle of law in the vehemently pragmatic application of that abstraction to the facts of a case is one of the most highly prized legal skills in the common law system. The lawyer is searching for the principles which underlined and underlay the court's decision.


  1. Wiktionary. Published under the Creative Commons Attribution/Share-Alike License.


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