Sources of Law

No single author

American law has no single author. Four institutions write it at once, each in its own way: the people ratify a constitution, legislatures vote statutes into force, agencies issue regulations, and courts decide cases and publish opinions. Those four are the primary sources, the law itself rather than anyone’s report of it. A textbook, an encyclopedia entry, or an AI summary is a secondary source, useful for orientation and never the authority. This reading is the map the activity assumes. It sets out what each source is, who makes it, how the four rank when they collide, and why you read a source yourself instead of trusting a summary of it. The activity then puts the map to work: an AI sketches how all four bear on one real issue, and you go find each source and test whether the sketch holds.

Four sources, four makers

Each primary source has a different maker, and three of the four line up with the branches of government. Legislatures write statutes. Executive-branch agencies issue the regulations that carry statutes into operation. Courts make case law when they decide disputes. The Constitution stands over all three, because it created them.

Start at the top. The Constitution builds the government, hands it its powers, and marks where those powers stop. Everything below it holds only while it stays inside those marks, so a statute that violates the Constitution is void however many votes it drew. Cornell’s Legal Information Institute (opens in a new tab) carries the text and all twenty-seven amendments. Each state has its own constitution, which does the same work inside that state and still answers to the federal one.

A statute is a law a legislature enacts, either Congress or a state legislature. Statutes are the written choices of elected lawmakers, and they are filed by subject into codes so the law on one topic sits in one place. Federal statutes live in the United States Code (opens in a new tab). A statute can override conflicting common law, and it still has to stay inside the constitution.

A regulation comes from an administrative agency instead of from a legislature. A statute rarely spells out every operating detail, so it hands an agency, such as the EPA or the SEC, authority to fill the gap with binding rules. The agency has to follow the procedures in the Administrative Procedure Act to use that authority. Final rules are compiled in the Code of Federal Regulations, and the current text sits on eCFR (opens in a new tab). One catch runs under all of it: a regulation is only as strong as the statute behind it. A rule that reaches past what its statute authorized can be struck down, so when you find a regulation, ask which statute lets the agency issue it.

The fourth source is case law, made in the written opinions courts issue when they decide real disputes. Courts create law two ways. They interpret the other three sources, and that reading becomes part of what each source means. Where the legislature has not spoken, they also build common law, doctrine worked out one decision at a time. A court does not only apply the law. It makes some of it.

How a decision becomes law

Case law behaves differently from a statute, and the difference is stare decisis, Latin for standing by things decided. A court follows the reasoning of earlier decisions when a later case raises the same question. The practice buys the system two things it needs: people can plan around settled rules, and like parties get like treatment.

Precedent does not bind every court the same way. A decision binds the courts under it in the same jurisdiction, and that is mandatory precedent. A decision from another jurisdiction, or from a lower court, may persuade and is worth weighing, though it controls nothing. A federal judge in Orlando has to follow the Eleventh Circuit, and may read a Ninth Circuit opinion on the same question, admire it, and rule the other way. So reading a case means asking who decided it, and whether that court’s word binds the court you care about.

The habit of reasoning from past decisions is inherited. It comes from the English common law, and the classic account is William Blackstone’s Commentaries (opens in a new tab), published in 1765 and assigned in the activity. Blackstone called judges the “living oracles” of the law, sworn to decide every doubtful case by the law of the land. American courts still work that way. Seeing where the habit began makes the case law you read less strange.

When sources disagree

Four sources make law at the same time, so sooner or later two of them point different ways. Supremacy and hierarchy of authority is the rule that settles which one wins. Inside a single system the order runs from the top down: the constitution, then the statutes passed under it, then the regulations issued under those. A statute that violates the constitution falls. A regulation that exceeds its statute falls. Each level answers to the one above it.

Picture a statute that tells an agency to set safety standards for ladders, and an agency that issues a rule on scaffolding. The rule may be sensible, and a court can still strike it down, because the statute never reached scaffolding. Good policy is not the test. Authority is.

Case law occupies no rung of its own. Its weight tracks whatever it interprets. A court’s reading of a statute carries that statute’s force, so the legislature can undo the reading by amending the statute. A court’s reading of the constitution carries constitutional force, which only the court itself or a constitutional amendment can change. That is why a Supreme Court decision about the Constitution is so hard to reverse.

A second axis crosses the first: federal law against state law. The Supremacy Clause settles that collision in favor of valid federal law, inside the areas the federal government properly governs. It does not make federal power unlimited. Within a state, the same top-down order repeats, from state constitution to state statute to state regulation, all of it still under federal law where federal law reaches.

Why you read the source yourself

Knowing the four sources and their order is half the skill. The other half is refusing to take anyone’s word for what a source says, and four sources give a careless summary four ways to go wrong. It can name a statute the legislature repealed years ago. It can quote a regulation as though the rule settled a question its statute answers differently. It can cite one trial judge’s decision as if it bound an entire state. It can invent the authority outright, pairing a real case name with a holding no court ever reached.

Language models fail in these ways in particular, because they are built to produce text that looks right. A plausible code section arrives attached to a rule it does not contain. That is a fact about the tool, and the inference for you is short: a citation you have not opened is a claim, not authority.

So the activity ends in verification. You will build a research map with an AI, then run every source it named to ground. Read the constitutional provision at Cornell, find the statute in the United States Code, and pull up the regulation on eCFR. For the case, pull the full opinion through Westlaw Campus (opens in a new tab) with your DSC login, or search Google Scholar (opens in a new tab) for free. Source triangulation is the name for that discipline, and training it is what the whole activity is for. Open the activity once the four sources feel steady. Expect the map to have a hole in it.