when did the doctrine of precedent begin to emerge in english common law
Common law The doctrine of precedent developed during the 12th and 13th centuries,[73] as the collective judicial decisions that were based in tradition, custom and precedent.[74]
Ex post facto law Some common-law jurisdictions do not permit retroactive criminal legislation, though new precedent generally applies to events that occurred before the judicial decision. Ex post facto laws are expressly forbidden by the United States Constitution in Article 1, Section 9, Clause 3 (with respect to federal laws) and Article 1, Section 10 (with respect to state laws). In some nations that follow the Westminster system of government, such as the United Kingdom, ex post facto laws are technically possible, because the doctrine of parliamentary supremacy allows Parliament to pass any law it wishes. In a nation with an entrenched bill of rights or a written constitution, ex post facto legislation may be prohibited.