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Jurisprudence

PLA 1003Activity 2·11 min read

Why it Matters

Every time someone says a law is “unfair,” they are importing a claim from moral philosophy into a legal dispute, whether or not they know it. This activity puts that instinct on the table by examining three foundational schools of legal theory — natural law, legal positivism, and legal realism — through a single vehicle: Fuller’s The Case of the Speluncean Explorers, where five fictional judges read the same murder statute, face the same facts, and reach different verdicts based on different theories of what law is and where it gets its authority. By the end, you should be able to recognize those frameworks in real legal arguments and use them to construct and criticize your own.

Current Context

On June 30, 2026, the Supreme Court decided Trump v. Barbara, holding that the Fourteenth Amendment’s Citizenship Clause guarantees citizenship to nearly all children born on U.S. soil and that Executive Order 14160 could not narrow it. The Court split 6-3 on the executive order and 5-4 on the constitutional question, across six opinions and 194 pages. Chief Justice Roberts traced the rule through English common law and early American practice, while Justice Alito answered that the majority had misread the original meaning of the Citizenship Clause and Justice Thomas argued that much of the governing 1898 precedent was dicta rather than binding law. Nine justices read one clause against one set of facts, and their disagreement runs on what makes a legal text binding rather than on what happened. That is the structure of Fuller’s Speluncean Explorers, running live in a case decided this summer.

Key Concepts

Jurisprudence

The philosophical study of what law is, where it derives its authority, and how it relates to morality and justice. It sits beneath every doctrinal debate: when lawyers argue about statutory interpretation or constitutional meaning, they are making jurisprudential moves, usually without saying so. This activity focuses on three schools — natural law, legal positivism, and legal realism — that give competing answers to the foundational question.

Natural Law

The theory that law derives its authority from universal moral principles discoverable through reason, not from human enactment alone. On this view, an unjust law is not merely a bad law — it is not truly law at all. Aquinas is the tradition’s most systematic expositor in the Western philosophical canon; MLK’s Letter from Birmingham Jail is its most powerful modern application.

The theory that law is valid because it was enacted by a legitimate authority through proper procedures, separate from any moral judgment about its content. A positivist judge applies the law as written — the alternative, they argue, invites judges to substitute personal moral preferences for the law’s clear commands. This is the dominant framework in most modern legal systems and the one most directly challenged by natural law claims.

The theory that law is best understood not as a formal system of rules but as a prediction of what courts will actually do, shaped by social, economic, and personal factors. On this view, the formal rules matter less than the judge, the facts, and the context. Holmes’s “bad man” thought experiment is legal realism’s most memorable formulation.

The “Bad Man” Theory

Holmes’s thought experiment in The Path of the Law: to understand what the law actually is, think from the perspective of a purely self-interested person who cares only about practical consequences, not about duty or morality. The bad man wants to know what courts will do to him — nothing more. The framing strips away moral language and defines law in entirely predictive, empirical terms.

Civil Disobedience

The deliberate, open violation of a law regarded as unjust, accepted without resistance, as a form of moral protest grounded in appeal to a higher principle. MLK’s Letter from Birmingham Jail offers its most rigorous modern argument: one has not only the right but the moral responsibility to refuse compliance with unjust laws. The concept is the pivot between legal theory and moral obligation in this activity.

Resources

What to Do

This activity uses one of the most famous exercises in legal education to develop a skill that applies in every course: the ability to identify the theory of law underlying an argument, not just the argument itself. Fuller’s The Case of the Speluncean Explorers places five fictional judges before the same murder statute and the same facts, and each reaches a different outcome. The reason is not the statute — it is each judge’s theory of what law is and how it should be read. Your job is to see those theories clearly, trace them to the primary texts, and then write as one of those judges.

Part 1: Read and Map the Philosophies

Begin with Fuller’s The Case of the Speluncean Explorers. As you read each opinion, note the reasoning structure each judge uses — you are not looking for the right answer, but for the logic each judge follows to reach his conclusion. Pay attention to what each judge treats as the source of law’s authority: the text of the statute, natural justice, or the practical consequences of the ruling. Use the Philosophy Mapper prompt to work through the connections between the judges’ arguments and the three schools of thought. The table it produces is a starting framework; verify it against the actual text before you rely on it.

Part 2: Connect to the Primary Sources

Trace the philosophical frameworks back to the sources on the resource list. The natural law judge echoes Aquinas’s claim that human law derives its force from natural law, and MLK’s distinction between just and unjust laws. The positivist judge applies the statute strictly, consistent with the tradition that validity comes from enactment, not moral content. The realist judge asks what outcome a sensible person in the real world could accept — the approach Holmes defends in The Path of the Law. Use the Opinion Architect prompt to develop these connections before you draft, working through how specific arguments in the primary texts support the judge’s position you intend to adopt.

Part 3: Write Your Judicial Opinion

Choose the judge you most agree with and write a judicial opinion of 400–600 words defending a decision to convict or acquit the explorers. The opinion must state your ruling and identify the legal philosophy it represents; defend your position by drawing on at least two of the primary texts from the resource list; and address the strongest argument against your position and explain why your view is still more compelling. Before you finalize, use the Counterargument Generator prompt to stress-test your reasoning. Treat the critique it returns as genuine pushback and revise your argument where the objection holds, and distinguish it where it does not.

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.

Philosophy Mapper

You are a jurisprudence professor analyzing The Case of the Speluncean Explorers by Lon L. Fuller (1949). Produce a table with three columns — Judge Name, Legal Philosophy (Natural Law / Legal Positivism / Legal Realism / Other, with specification), and Key Reasoning (two sentences on the main argument each judge uses to reach his conclusion) — for all five judges: Truepenny, Foster, Tatting, Keen, and Handy. After the table, identify the two judges most directly in conflict and explain in three sentences what their disagreement reveals about the fundamental divide between natural law and legal positivism. Base your analysis on Fuller’s text as written; do not import interpretations from secondary sources.

This prompt uses role assignment, structured output (the table), and a source-grounding constraint. The table format forces the model to address all five judges systematically rather than emphasizing whichever one seems most interesting. The follow-up synthesis question — which two judges are most in conflict? — shifts the exercise from description to analysis. You can build on the output in Part 2 by asking the AI to map each judge’s reasoning to a specific passage in one of the primary texts; that handoff is itself a basic chaining technique used in more complex AI workflows.

Opinion Architect

I am writing a judicial opinion in The Case of the Speluncean Explorers, siding with [name the judge] and his position that the explorers should be [convicted / acquitted]. Walk me through building my argument step by step. First, state the central legal principle my chosen judge relies on and explain in plain terms what it means. Second, identify the single strongest argument from [choose: MLK’s Letter from Birmingham Jail / Holmes’s The Path of the Law / Bastiat’s The Law / Aquinas’s Summa Theologica, Q.90–114 / William Blackstone, Commentaries on the Laws of England, vol. 1, Introduction, § 2 “On the Nature of Laws in General”] that supports that principle — describe the argument without quoting at length. Third, identify the strongest opposing argument I will need to address and suggest how my judge would respond to it. After completing all three steps, ask me one clarifying question about my position before we continue.

This prompt uses step-by-step decomposition to break a complex writing task into manageable parts. The Socratic move at the end — asking the student a clarifying question before proceeding — models a prompting technique worth reusing: instructing the AI to elicit information before generating output produces better-calibrated responses than asking it to produce a complete answer from sparse input. Notice that the bracket in the second step requires you to choose a primary source; that choice is part of your intellectual work, not the AI’s.

Counterargument Generator

I have drafted a judicial opinion in The Case of the Speluncean Explorers that argues [briefly state your ruling and the main reason]. Act as the judge in the case who most strongly disagrees with my position. Identify my weakest logical point, the specific primary text I am using in a way that could be questioned, and the one factual or legal consideration I appear to be ignoring. Be direct. I do not want a balanced assessment; I want the best possible case against my argument so I can strengthen it before I submit. Here is my draft: [paste your opinion here].

Red-teaming — asking the AI to argue against your position rather than evaluate it — consistently produces sharper, more useful output than a neutral review. Models default toward validation; the adversarial framing works against that tendency. Pay attention to which objections hold and which you can answer: the ones you cannot answer easily are the ones worth revising before submission. The judgment about which objections matter is yours to make.

Primary Source Navigator

I am about to read [choose one: Thomas Aquinas’s Summa Theologica, Q.90–114 / Oliver Wendell Holmes’s “The Path of the Law” / Frédéric Bastiat’s The Law / Martin Luther King Jr.’s “Letter from Birmingham Jail” / William Blackstone, Commentaries on the Laws of England, vol. 1, Introduction, § 2 “On the Nature of Laws in General”]. Give me a brief orientation in four parts: (1) who the author was and the historical moment that shaped this text, (2) the central argument I should watch for as I read, (3) the one section or passage most directly relevant to the debate in The Case of the Speluncean Explorers, and (4) one question I should hold in mind while reading to connect this text to Fuller’s case. After I read, I will return and tell you what I found — at that point, I want you to check my reading against what the text actually says and flag anything I may have overstated or missed.

This prompt works as a reusable template: you can run it for any of the four primary texts in this activity simply by changing the bracket. The closing instruction — asking the AI to check your reading against the source — builds verification into the workflow rather than treating the AI as an authority. That habit matters: AI tools regularly produce confident paraphrases of philosophical texts that subtly distort the original argument. Reading the text yourself and returning with your own interpretation before asking the AI to critique it is the right sequence, not the reverse.

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