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Sources of Law

PLA 1003Activity 5

Why it Matters

A legal question has an address, and your first job is knowing which of four doors to knock on. American law comes from a constitution, from statutes the legislature passes, from regulations agencies issue, and from decisions courts hand down. Those four do not carry equal weight, so when they collide, one controls and the rest give way. Trace a rule to its source and you can say whether it is current, whether it says what someone claims it says, and whether a higher authority has already overridden it. Take the claim on faith and you are trading law for rumor, which is what an AI tool hands you when you stop reading the source yourself.

Current Context

On July 2, 2026, the U.S. Court of Federal Claims ruled that the Treasury Department never had the authority to issue Treasury Regulation Section 1.951A-2(c)(5) (opens in a new tab). Treasury had written the rule to patch a mismatch Congress built into the 2017 tax act’s global intangible low-taxed income provisions. The court read the statute itself rather than defer to the agency, the independent judgment the Supreme Court required when it discarded Chevron in 2024 (opens in a new tab). Read that way, the subsection never mentions the Secretary at all. A regulation is worth only as much as the statute behind it, and a court, not the agency, decides how far that statute reaches.

Key Concepts

Constitution

A founding document that creates a government, hands it its powers, and fences those powers in. The federal Constitution sits at the top of the American hierarchy, so every other source of law gives way to it. Each state has its own constitution, which plays that same role inside the state.

Statute

A law a legislature enacts, whether Congress or a state legislature. Statutes are gathered by subject into codes, such as the United States Code, so a researcher can find the law on one topic in one place. A statute overrides conflicting common law, and it still has to stay inside the constitution.

Regulation

A binding rule an agency issues under authority a statute delegates to it. Legislatures leave the operating detail open, and agencies fill it in by following the procedures the Administrative Procedure Act sets. Final regulations are compiled in the Code of Federal Regulations.

Case Law

Law made in the written opinions courts issue when they decide real disputes. When a court interprets a statute, a regulation, or the constitution, that reading becomes part of what everyone else must follow. Courts also build common law, the doctrine worked out decision by decision where the legislature has not spoken.

Stare Decisis

The principle that a court follows the reasoning of earlier decisions when a later case raises the same question. It makes the law predictable and treats like parties alike. Precedent from a higher court binds the courts under it in the same jurisdiction.

Supremacy and Hierarchy of Authority

The ordering rule that decides which source controls when sources conflict. The federal Constitution is supreme, then federal statutes and treaties, then federal regulations, with the case law interpreting each carrying that source’s weight. The Supremacy Clause settles a genuine conflict between federal and state law in favor of federal law, within the sphere the federal government properly governs.

Administrative Agency

A government body a statute creates and charges with one area of law, such as the EPA or the SEC. An agency issues regulations, enforces them, and decides disputes inside its own jurisdiction. It sits in the executive branch, and the work it does reaches into all three.

Resources

What to Do

This activity trains you to check a legal claim against the source it came from. You will have an AI map how the four primary sources bear on one real situation. Then you find the constitution, statute, regulation, and case behind that map and test whether the AI told the truth. The skill is source triangulation: you accept a legal claim, from an AI or from anyone else, only after tracing it to authority you can read for yourself.

Part 1: Build Your Foundation

Get the landscape straight in your own head before you test anything against it. Run Sources and Lawmaking Explainer for a plain account of the four primary sources, how they rank, and how a bill becomes a statute while an agency turns statutory authority into a binding rule. Then read Blackstone’s Section the Third, listed in Resources, and run Blackstone Translator on any passage that resists a modern reader. Blackstone is where the common law habit of reasoning from past decisions enters the tradition you are studying, so spend real time with his sentences rather than the AI’s gloss on them.

Part 2: Generate a Research Map

Pick a current legal issue that interests you. Run Case Study Mapper to produce a short account of how the Constitution, a statute, an agency regulation, and recent case law each bear on it. Treat what comes back as a map, not the territory. The AI will name specific provisions, statutes, regulations, and cases, so write each one down exactly as the AI states it. Part 3 checks every one of those claims against the source itself.

Part 3: Verify Against the Sources

This is the core of the activity. Take the map from Part 2 and find each primary source the AI named. Read the constitutional provision in the text at Cornell’s Legal Information Institute. Find the statute in the United States Code and read the section, not a summary of it. Locate the regulation in the eCFR. Pull the case through Westlaw Campus from the library, or use Google Scholar’s case law search, and read what the court actually held. Run Citation Auditor as you go, and keep a running log of what the AI got right and what it got wrong. Flag anything it invented outright, such as a statute that does not exist or a case that does not hold what the AI claimed. Note especially any place where reading the original changed your understanding of the issue.

Part 4: Write Your Findings (400 to 600 words)

Write up what you found. Open by naming the issue you investigated so a reader has context. Then give the body of the post to one comparison: the widest gap between the AI’s summary and the actual text of a statute, regulation, or opinion you read. Say which of the four sources was hardest to find or to understand, and why. Close by explaining how digging for the originals changed your sense of where law comes from, and state your single most important takeaway. Keep the post between 400 and 600 words.

Include one AI chat link with a 1–2 sentence explanation of what the conversation shows and why you chose to share it.

Suggested AI Prompts

Use these prompts as a starting point, then adjust them to fit your goal. Strong prompting develops through trial, revision, and testing. It’s a foundational skill that grows into more advanced AI work such as context engineering and agent-based workflows.

Sources and Lawmaking Explainer

You are explaining the U.S. legal system to a college student in an Introduction to Law course who is new to legal study. Write in full paragraphs, with no bullet points. First, explain the four primary sources of American law: constitutional law, statutory law, administrative regulations, and case law. For each, describe where it comes from, what authority it carries, and how it works in practice, and connect it to the branch of government that produces it. Define the terms statute, regulation, judicial precedent, and administrative agency as you use them. Then explain the hierarchy among them: why the Constitution is supreme, how statutes relate to regulations, and how courts interpret and apply both. Next, walk me through how Congress turns a bill into a statute: introduction, committee review, floor debate, voting, reconciliation between the chambers, and presidential action, defining terms like markup, conference committee, and veto override as they come up. Then explain how Congress delegates authority to an agency through enabling legislation, and how the agency uses that authority to make a binding rule through notice-and-comment rulemaking under the Administrative Procedure Act: proposed rule, publication in the Federal Register, public comment, and final rule. Finish by explaining where statutes end up (the United States Code) and where final regulations end up (the Code of Federal Regulations). Keep the language precise but accessible to someone encountering legal terminology for the first time.

Naming the four sources, the terms to define, and the stages of each process is decomposition: one large question broken into ordered parts the model answers in sequence. That sequencing is the same move behind multi-step AI workflows, where each stage feeds the next.

Blackstone Translator

I am reading William Blackstone’s Commentaries on the Laws of England, Volume 1, Introduction, Section the Third, titled “Of the Laws of England” (1765). I will paste passages from it. Rewrite each passage in plain modern English while keeping its legal precision and its reasoning intact. Do not flatten the distinctions Blackstone is drawing. Leave any Latin phrases or legal maxims as they appear, and explain them briefly only when needed for clarity. Keep the tone formal and the output in full paragraphs. After each rewrite, note in one sentence anything in the passage that connects to how American courts still reason from precedent today.

Pasting the passage and asking for a translation rather than a summary keeps Blackstone’s own text as the anchor. You can then hold the rewrite against his words, which is impossible with a paraphrase of a source you never read.

Case Study Mapper

You are helping a college student in an Introduction to Law course see how the four primary sources of American law interact in one real situation. Research a current legal or policy issue or court case from within the last twelve months in which the U.S. Constitution, a statute, an agency regulation, and recent case law all play a part. In full paragraphs, identify the issue, then explain the constitutional provision or right involved, the specific statute that applies, the specific agency regulation at issue, and how courts have recently interpreted or enforced the law. For every source, give the exact citation: the article or amendment, the United States Code title and section, the Code of Federal Regulations citation, and the case name with court and year, so each one can be looked up and verified.

Demanding an exact citation for every source turns a vague narrative into a set of checkable claims. That is deliberate, because Part 3 sends you to the primary source to verify each one.

Citation Auditor

I am going to give you a legal summary an AI produced, along with the citations it included: a constitutional provision, a United States Code section, a Code of Federal Regulations citation, and a case name. For each citation, tell me what to look for when I check it against the primary source, and what would tell me the AI got it wrong, fabricated it, or described it inaccurately. Do not confirm that any citation is correct on your own authority, and say plainly that the only way to know is for me to read the actual constitutional text, statute, regulation, and opinion myself. Give me a short checklist I can use as I verify each one.

The prompt treats the AI as a verification aid and blocks the model from vouching for its own citations. Models invent statutes and cases that look plausible, so checking every authority against the primary source is the safeguard that matters most in AI-assisted legal research.

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