A judicial precedent in England has authority of law it is not merely evidence of law but is its source and the courts must follow it when established. Neither Roman law nor any other modern system of law allows such importance or authority to precedent.
Professor Kecton observes that the following of precedent is easier in England than in many other countries, firstly, because the system of justice is centralized and there is a comparatively small number of reported cases; secondly, because there is no written constitution which could be made unworkable if cases deciding its interpretation where made binding; and, thirdly, because the legislature has absolute power to remedy any particular defect.
The radio decidedness of a decision contains the principle of law formulated by a judge. It has to be distinguished from an orbiter dictate which is not essential for the decision of a case and may even be answers to hypothetical questions and as such has not the force of law. The underlying principle of a judicial decision, which is only authoritative, is termed the ratio decided.
As Salmond observes, the concrete decision is binding between the parties to, it but it is the abstract ratio decides which alone has the force of law as regards the world at large.
The courts while deciding questions on principle have either to follow an already existing rule of law, or if there is no authority, to formulate some general rule and to act upon it. In so formulating the rule they must contain themselves to the requirements of the case in hand.
“The only judicial principles which are authoritative” to quote Salmond again, ‘are those which are thus relevant in their subject-matter and limited to their scope. All others, at the best, are of merely persuasive efficacy. They are not true rationes decidendi and are distinguished from them under the name of dicta or obiter dicta, things said by the way.”