"The principle or principles of law on which the court reaches its decision" Dictionary of Law, OUP, 1997

In common law systems, which follow a system of Legal precedent, case law, along with statute, evolves the law. Generally speaking, a court's decision in one case is binding in future cases of similar fact. Exceptions to this are (in English law):

  • Where the original decision was made per incuriam (in error) or was too obscure
  • Where the original decision was made in a lower court
  • In the House of Lords, which can overturn any existing precedent from lower courts, or from a previous case in the House of Lords itself.
In order to establish a case's authority over a later case, it is crucial in these systems to establish its ratio decidendi (decidendi often drops off in casual usage, abbreviating the term to ratio).

So, how do you go about finding the ratio?

The easiest way for the layman will be to look at newspaper law reports of a case. Although newspaper reports do not hold quite the same status as official reports, they may be cited in a court, and are a good deal shorter than the official publications. The report will generally break down into1:

  1. Identifying the case
  2. Establishing the facts of the case
  3. Arguing the case
  4. History of the case
  5. Argument
  6. Ratio Decidendi
  7. Judgment
So at least that narrows down where you need to look to find the ratio. It won't always be clear which particular sentence or statement contains the ratio. If you are reading a newspaper law report, however, you will often find the ratio introduced by the name of the Judge and the words 'said that', or something similar.

If you have a little more time on your hands, and convenient access, you could always read through the full text in one of the official Law reports. However, you'll need to read through a great deal of establishing, arguing, and history, including extensive earlier case law, before you reach the crucial ratio statement.

To take a real case, and one which will be familiar to any students of English Law, in Donoghue v Stevenson (1932), the facts of the case were these: that Mrs Donoghue's friend had bought for her a bottle of ginger beer at a café, and that said bottle contained a dead snail. Mrs D was not overjoyed about this, but unfortunately as she had not bought the ginger beer herself she could not pursue a case under Contract Law against the café owner. So she sued Stevenson, the manufacturer of the ginger beer. The ratio of the case, was thus that:

'...a manufacturer of products, which he sells in such a form as to show that he intends them to reach the ultimate consumer in the form in which they left him with no reasonable possibility of intermediate examination and with the knowledge that the absence of reasonable care in the preparation or putting up of the products will result in an injury to the consumer's life or property, owes a duty to the consumer to take that reasonable care', per Lord Atkin 1932 AC 562, 599.

The Lords held three to two that the manufacturer was indeed liable, and established a precedent binding on all English courts. Note the narrowness of the ratio in this case: this decision is only strictly binding on cases where the ratio can be similarly distilled. If the ratio of a future case differs sufficiently from an earlier ratio, the ratio from the earlier case has persuasive authority only (it's a good argument, and should be considered), just as obiter dicta do.

Although the ratio in Donoghue v Stevenson was narrowly defined, the Law Lords allowed themselves the chance to establish, obiter dictum, what has since become known as 'the neighbour principle'2. Remember, though, that the neighbour principle was not the ratio of the case. It was, however, a very good argument, and has found widespread application.

  1. Bhatia, V. K. (1993): Analysing Genre: Language Use in Professional Settings. Applied Linguistics and Language Study. London: Longman.
  2. "The rule that you are to love your neighbour becomes in law, you must not injure your neighbour; and the lawyer's question, Who is my neighbour? receives a restricted reply. You must take reasonable care to avoid acts or omission which you can reasonably foresee would be likely to injure your neighbour. Who then, in law, is my neighbour? The answer seems to be - persons who are so closely and directly affected by my act that I ought reasonably to have them in contemplation as being so affected when I am directing my mind to the acts or omissions which are called in question.", per Lord Atkin 1932 AC 562, 580.

    In other words, if I'm careless and you get hurt, you can claim compensation, but at the same time, I won't be expected to compensate absolutely everyone who was injured as a consequence of my carelessness.

You might be interested in:

  • http://www.lawscot.org.uk/whatis/case5.html
  • http://www.leeds.ac.uk/law/hamlyn/donoghue.htm - the full text of the case
  • http://www.celt.stir.ac.uk/staff/Badger/RATIO.HTM - "a preliminary investigation of the identification of the ratio decidendi in law reports"

Please /msg me regarding any mistakes, omissions, oversights, or ambiguities.

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