Cannon of Construction
Also known as canons of construction, canons give common sense guidance to courts in interpreting the meaning of statutes. Most canons emerge from the common law process through the choices of judges. Proponents of the use of canons argue that the canons constrain judges and limit the ability of the courts to legislate from the bench. Critics argue that a judge always has a choice between competing canons that lead to different results, so judicial discretion is only hidden through the use of canons, not reduced.
Textual canons are rules of thumb for understanding the words of the text. Some of the canons are still known by their traditional Latin names.
When writing statutes, the legislature intends to use ordinary English words in their ordinary senses. The United States Supreme Court discussed the plain meaning rule in Caminetti v. United States, 242 U.S. 470 (1917), reasoning
"[i]t is elementary that the meaning of a statute must, in the first instance, be sought in the language in which the act is framed, and if that is plain... the sole function of the courts is to enforce it according to its terms." And if a statute's language is plain and clear, the Court further warned that "the duty of interpretation does not arise, and the rules which are to aid doubtful meanings need no discussion."
Ejusdem generis (Of the same kinds, class, or nature)
When a list of two or more specific descriptors is followed by more general descriptors, the otherwise wide meaning of the general descriptors must be restricted to the same class, if any, of the specific words that precede them. For example, where "cars, motor bikes, motor powered vehicles" are mentioned, the word "vehicles" would be interpreted in a limited sense (therefore vehicles cannot be interpreted as including airplanes).
Expressio unius est exclusio alterius' (The express mention of one thing excludes all others) : Items not on the list are assumed not to be covered by the statute. However, sometimes a list in a statute is illustrative, not exclusionary. This is usually indicated by a word such as "includes" or "such as."
In pari materia (Upon the same matter or subject)
When a statute is ambiguous, its meaning may be determined in light of other statutes on the same subject matter.
Noscitur a sociis (A word is known by the company it keeps)
When a word is ambiguous, its meaning may be determined by reference to the rest of the statute.
Reddendo singula singulis (Refers only to the last)
When a list of words has a modifying phrase at the end, the phrase refers only to the last, e.g., firemen, policemen, and doctors in a hospital.
Generalia specialibus non derogant
Described in The Vera Cruz (1884) 10 App. Cas. 59 as: "Now if anything be certain it is this, that where there are general words in a later Act capable of reasonable and sensible application without extending them to subjects specially dealt with by earlier legislation, you are not to hold that earlier legislation indirectly repealed, altered, or derogated from merely by force of such general words, without any evidence of a particular intention to do so." This means that if a later law and an earlier law are potentially - but not necessarily - in conflict, courts will adopt the reading that does not result in an implied repeal of the earlier statute. Lawmaking bodies usually need to be explicit if they intend to repeal an earlier law.
Substantive canons instruct the court to favor interpretations that promote certain values or policy results.
"Charming Betsy" Canon
National statute must be construed so as not to conflict with international law. See Murray v. The Charming Betsy, 6 U.S. (2 Cranch) 64 (1804): "It has also been observed that an act of Congress ought never to be construed to violate the law of nations if any other possible construction remains..."
Interpretation in Light of Fundamental Values