Ratio decidendi
Ratio 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
A court is a form of tribunal, often a governmental institution, with the authority to adjudicate legal disputes between parties and carry out the administration of justice in civil, criminal, and administrative matters in accordance with the rule of law...

 to compose the rationale of a particular judgment. Unlike obiter dicta
Obiter dictum
Obiter dictum is Latin for a statement "said in passing". An obiter dictum is a remark or observation made by a judge that, although included in the body of the court's opinion, does not form a necessary part of the court's decision...

, the ratio decidendi is, as a general rule, binding
Binding precedent
In law, a binding precedent is a precedent which must be followed by all lower courts under common law legal systems. In English law it is usually created by the decision of a higher court, such as the Supreme Court of the United Kingdom, which took over the judicial functions of the House of...

 on courts of lower and later jurisdiction—through the doctrine of stare decisis
Stare decisis
Stare decisis is a legal principle by which judges are obliged to respect the precedents established by prior decisions...

. Certain courts are able to overrule decisions of a court of co-ordinate jurisdiction—however out of interests of judicial comity
In law, comity specifically refers to legal reciprocity—the principle that one jurisdiction will extend certain courtesies to other nations , particularly by recognizing the validity and effect of their executive, legislative, and judicial acts...

 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
A lawyer, according to Black's Law Dictionary, is "a person learned in the law; as an attorney, counsel or solicitor; a person who is practicing law." Law is the system of rules of conduct established by the sovereign government of a society to correct wrongs, maintain the stability of political...

. With a proper understanding of the ratio of a precedent
In common law legal systems, a precedent or authority is a principle or rule established in a legal case that a court or other judicial body may apply when deciding subsequent cases with similar issues or facts...

, 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 fact
A fact is something that has really occurred or is actually the case. The usual test for a statement of fact is verifiability, that is whether it can be shown to correspond to experience. Standard reference works are often used to check facts...

s of the case.

The search for the ratio of a case is a process of elucidation; one searches the judgment for the abstract
Abstraction is a process by which higher concepts are derived from the usage and classification of literal concepts, first principles, or other methods....

 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
Donoghue v. Stevenson
Donoghue v Stevenson [1932] UKHL 100 was a decision of the House of Lords that established the modern concept of negligence in Scots law and English law, by setting out general principles whereby one person would owe another person a duty of care...

would be that a person owes a duty of care
Duty of care
In tort law, a duty of care is a legal obligation imposed on an individual requiring that they adhere to a standard of reasonable care while performing any acts that could foreseeably harm others. It is the first element that must be established to proceed with an action in negligence. The claimant...

 to those who he can reasonably foresee will be affected by his actions.

All decisions are, in the common law
Common law
Common law is law developed by judges through decisions of courts and similar tribunals rather than through legislative statutes or executive branch action...

 system, decisions on the law as applied to the facts of the case. Academic or theoretical points of law
Law is a system of rules and guidelines which are enforced through social institutions to govern behavior, wherever possible. It shapes politics, economics and society in numerous ways and serves as a social mediator of relations between people. Contract law regulates everything from buying a bus...

 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
In common law legal systems, a precedent or authority is a principle or rule established in a legal case that a court or other judicial body may apply when deciding subsequent cases with similar issues or facts...

, but is instead called an obiter dictum
Obiter dictum
Obiter dictum is Latin for a statement "said in passing". An obiter dictum is a remark or observation made by a judge that, although included in the body of the court's opinion, does not form a necessary part of the court's decision...


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
    Supreme court
    A supreme court is the highest court within the hierarchy of many legal jurisdictions. Other descriptions for such courts include court of last resort, instance court, judgment court, high court, or apex court...

     versus an appellate court
    Appellate court
    An appellate court, commonly called an appeals court or court of appeals or appeal court , is any court of law that is empowered to hear an appeal of a trial court or other lower tribunal...

  • 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.


The difficulty in the search for the ratio becomes acute when, as is never the case in the decisions of the Court of Appeal or the House of Lords
House of Lords
The House of Lords is the upper house of the Parliament of the United Kingdom. Like the House of Commons, it meets in the Palace of Westminster....

, more than one judgment is promulgated. A dissenting judgment on the point is not binding, and cannot be the ratio. However, one will sometimes find decisions in which, for example, five judges are sitting the House of Lords, all of whom purport to agree with one another but in each of whose opinion
In general, an opinion is a subjective belief, and is the result of emotion or interpretation of facts. An opinion may be supported by an argument, although people may draw opposing opinions from the same set of facts. Opinions rarely change without new arguments being presented...

s one is able to discern subtly different ratios. An example is the case of Kay v. Lambeth LBC
Kay v. Lambeth LBC
Kay v Lambeth London Borough Council was a case in the House of Lords relevant for English property law, UK human rights and English tort law case involving claims for possession by Lambeth London Borough Council against a "group of former short-life occupiers".-Judgment:In the House of Lords it...

, on which a panel of seven of their Lordships sat, and from whose opinions emerged a number of competing ratios, some made express by their Lordships and others implicit in the decision.

Another problem may arise in older cases where the ratio and obiter are not explicitly separated, as they are today. In such a case, it may be difficult to locate the ratio, and on occasion, the courts have been unable to do so.

Such interpretative ambiguity is inevitable in any word-bound system. Codification of the law, such as has occurred in many systems based on Roman law
Roman law
Roman law is the legal system of ancient Rome, and the legal developments which occurred before the 7th century AD — when the Roman–Byzantine state adopted Greek as the language of government. The development of Roman law comprises more than a thousand years of jurisprudence — from the Twelve...

, may assist to some extent in clarification of principle, but is considered by some common lawyers anathema to the robust, pragmatic and fact-bound system of English law
English law
English law is the legal system of England and Wales, and is the basis of common law legal systems used in most Commonwealth countries and the United States except Louisiana...


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