Statutory interpretation

When a court needs to apply a law to a case, it often has to figure out what the law actually means. This process is called statutory interpretation. In common law systems, judges use this method for both laws passed by legislatures and for rules made by government agencies. Sometimes a statute’s wording is clear, but often there is ambiguity that the judge must resolve.

The need for formal statutory interpretation grew in common law countries, especially England. Unlike Roman or civil law systems, where a code guides a magistrate without creating binding precedent, English courts built the common law over time. Since Parliament did not create a complete legal code, judges made decisions that became binding on later courts. Once a particular interpretation of a statute became binding, a consistent framework was needed. The main goal was to carry out the "intention of Parliament," and English courts developed three main rules: the mischief rule, the literal rule, and the golden rule.

Courts also assume that statutes include certain elements, because Parliament is presumed to have intended them. For example, criminal offenses are presumed to require a guilty mind (*mens rea*), as in *Sweet v Parsley*. A statute is presumed not to change the common law, not to take away personal liberty, vested rights, or property, and not to apply to the Crown. It is also presumed not to allow someone to commit a crime, not to apply retroactively (the common law is "declaratory," as in *Shaw v DPP*), and to be interpreted in line with international treaties the UK has joined. Under EU law, any statute that contradicts the principle of EU supremacy is effectively void, as in *Factortame*. Words in a statute are to be read *ejusdem generis*—in sympathy with their immediate context. When legislation and case law conflict, legislation takes precedence, a principle known in the UK as parliamentary sovereignty. But while Parliament alone makes laws, the courts alone interpret them.

General principles of interpretation have developed over time. As Cross put it, interpretation is how courts determine a statute’s meaning for a specific case. Salmond called it the process of finding the legislature’s meaning through the authoritative forms in which it is expressed. How a statute is interpreted depends on how much creativity a judge applies. While the golden, mischief, and literal rules are often mentioned, Francis Bennion noted that there are no simple devices—instead, there are many interpretative criteria.

A statute is an edict from a legislature, and the usual way to interpret it is to seek the "intention" of its maker. Courts must act on the true intention of the legislature, or *mens sententiae legis*. If a provision has more than one meaning, the court must choose the one that reflects the legislature’s true intention. The court’s job is to explain the law, not to create it.

In federal systems, there can be conflicts between federal and local law. In Canada, when both levels of government have concurrent jurisdiction, federal law is paramount. But if the Canadian constitution is silent on an area, it must be interpreted as falling under either the federal residual power (the "Peace, Order and Good Government" clause in section 91) or the provincial residual power over "Property and Civil Rights" in section 92(13A) of the 1867 Constitution Act. This differs from the United States and Australia, where if federal legislation is not based on a specific constitutional provision, the states have authority over the matter, unless otherwise stated.