Why common law judges look backward before they decide
A judge in a common law country rarely starts from scratch. Earlier rulings on similar questions act as authority, and lower courts must follow those from above. Yet only the core reasoning binds; a judge's passing remarks can be quoted as persuasive, but nobody is obliged to obey them.
The principle is called stare decisis, shortened from a Latin phrase urging courts to stand by what has been decided and leave settled matters undisturbed. It works in two directions. Vertically, a lower court must follow rulings of higher courts in its jurisdiction, as a federal appeals court follows the US Supreme Court. Horizontally, a court sticks with its own past decisions. The modern Supreme Court departs from its earlier rulings only when there is a special justification, rejecting a rigid version that would preserve past mistakes regardless of consequences.
What binds is the ratio decidendi, the reasoning that actually carries the judgment. Obiter dicta, remarks said in passing, are not required to settle the dispute. A later court facing an old case can apply it, distinguish it because the facts differ materially, or overrule it as wrong or outdated. Decisions from neighbouring jurisdictions count only as persuasive; courts in Australia and Hong Kong, for instance, weigh rulings from Britain. When no earlier authority exists at all, the court faces a case of first impression.
The system depends on publication, because precedent only helps when lawyers can find it. Judges can choose not to publish some opinions, and settlements create no precedent, which is why the US Justice Department sometimes settles simply to avoid an unfavourable ruling. In American federalism, federal courts deciding state-law questions must follow state courts under the Erie doctrine.
Civil law countries follow a different logic, since only legislatures are supposed to make law. Their courts rely on jurisprudence constante: a consistent line of reasoned rulings is highly persuasive without being controlling. French judgments tend to be terse, leaving academics to explain the reasoning, while German courts cite earlier cases more freely. Mixed systems such as Scotland, South Africa, Quebec and Louisiana blend both approaches.
Source: Precedent
