Under the tripartite structure of the U.S. federal government (See: Separation of powers), it is the authority of courts to construe what the law is, as Chief Justice John Marshall affirmed in the milestone case Marbury v. Madison (See also: Judicial Review). When the court decides what the law means, the prevailing view is that it is not the judge's responsibility to make the law, but to interpret the law. The two dominant theories of legal interpretation - purposivism and textualism - take different positions on how judges can best adhere to this ideal of legislative supremacy. The problem is particularly acute in situations where Congress is unlikely to anticipate and legislate for the particular circumstances at issue in the courts. Purposivists argue that courts should prioritize interpretations that advance the purpose of a statute, while textualists argue that judges' concerns should be limited primarily to the text of the statute.
Regardless of their different theories of interpretation, judges may use many similar tools to gather evidence of statutory meaning. First, judges usually begin by looking for the plain meaning of a legal text. Second, courts interpret specific provisions by looking at their broader legal context. Third, judges may turn to the canons of construction, which are inferences about how courts typically read statutes. Fourth, a court may look to the legislative history of a particular provision. Finally, judges may consider how a statute has been or will be enforced. Although both purposivists and textualists may use any of these tools, a judge's theory of legal interpretation may influence the order in which they are applied and the weight to be given to each tool.
[Last updated in July of 2021 by the Wex Definitions Team]