Authority in legal research and writing is a description of the need for legal arguments to reference key sources that will support their writing.
Authority is driven from two categories of resource, primary and secondary. Usually called statutes in legal terminology, the laws referenced as primary research come from the text of the statute as approved by a legislature. In essence, when the research references a particular law, rule, or code as written, then it is a primary source.
Secondary sources refer to any material that has been written in reference to the written word of law, as a means of interpretation. Therefore, secondary sources can be fairly tricky when examining them for the purposes of authority, because some secondary sources hold greater legal merit that others.
As a general rule, secondary sources that hold the greatest authority in legal writing are those that represent official actions of the court, such as opinions and precedents. When opinions come from higher courts, where decisions are rendered by a panel of justices (judges), there is a high frequency for there to be dissenting, minority opinions, which are usually also written down in the form of a minority opinion.
Precedents are usually opinions where a decision rendered upon a law sets a standard interpretation of a statute that dictates how that law should be followed. If a higher court examines a case that set the precedent an reinterprets the law or renders that law invalid (unconstitutional), then that precedent returns to being a majority opinion of a lower court.
Other elements of authority can be used in legal argument, such as treatises or articles by reputable scholars and authorities in the field of the law, but they will always hold a lower authority than written rule of the law or judicial opinion.