Figure 1.3
The U.S. Constitution is known as the supreme law of the land. (Credit: lynn0101/ pixabay/
License: CC0)
American Common Law
As discussed in the previous section, the United States follows the common law legal tradition of English law.
Judges in the Common Law system help shape the law through their rulings and interpretations. This body of
past decisions is known as case law, which is used by judges to inform their own rulings. In fact, judges rely on
precedent, i.e., previous court rulings on similar cases, when determining the ruling in their own cases.
An example of how case law works is the case of the State v. Wayfair Inc. (2017 SD 56, 901 N.W.2d 754 (S.D.
2017), cert. granted, 138 S. Ct. 735 (2018)), in which the South Dakota Supreme Court held that a state law
requiring internet retailers without an in-state physical presence to remit sales tax was unconstitutional.
Unless this ruling is overruled by the United States Supreme Court, then it becomes part of the case law and
precedent set in that state, and it will be followed by subsequent rulings when similar cases are filed.
Federal Law
The Constitution empowers federal law making by giving Congress the power to enact statutes for certain
limited purposes, like regulating interstate commerce. Federal law preempts conflicting state and local laws.
However, federal preemption is not without limits, insofar as states each have their own constitution and are
considered sovereign. Therefore, federal law may only preempt state law if it is enacted within the limited
powers that are enumerated and granted to Congress in the Constitution.
Broad interpretations of the Constitution’s Commerce and Spending Clauses have expanded the reach of
federal law into many areas. Indeed, its reach in some areas, such as aviation and railroads, is now so broad
that it preempts virtually all state law. In others areas, such as family law, lawmaking continues to be left to the
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Chapter 1 American Law, Legal Reasoning, and the Legal System
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