How to Reason Like a Natural Lawyer (Without Abandoning Rational Analysis)

You’ve got a memo due Thursday. The precedent your partner loves runs on a sentence like, “The law will not countenance an absurd result.” In this office, that phrase is a punchline. It sounds, they say, like natural law. So you have two problems: the memo, and a vague suspicion that the man you work for is right to snort.

Natural law has an image problem. Mention it at a bar exam review or a law-and-economics lunch and you get the same eyebrow. Someone asks if you’ve met Aquinas, in a tone that suggests you’d be friends and ride a donkey together.

Here’s the kicker: natural law theory is not a religious artifact. It is a rational discipline about law’s purpose, its moral limits and the point at which a “valid” statute stops being an obligation. And you already touch its edges every time you apply the plain meaning rule, weigh legislative purpose, or invoke constitutional morality.

Let’s walk through how to do it rigorously—without once appealing to a thunderstorm on Mount Sinai.

The Problem: Rationality Is Not the Enemy of the Question

Somewhere between Hobbes and the AmericanLegal Realists, law got an unhelpful haircut. The working assumption goes: a rule is law if it was made by the right institution, through the right procedure. Morality is an intervention, not an ingredient.

That view—legal positivism—does a lot of honest descriptive work. Hans Kelsen and H.L.A. Hart gave us clean tools to separate “law” from “rule of the gun.” We talk easier about validity, hierarchy and obligation because of them.

But then a problem shows up. Consider a statute that authorizes retroactive punishment. Or one that says judges may decide cases by flipping a coin. Nobody—including legal positivists—really wants to call that law without an asterisk.

Notice: you have just asked a rational question about the moral point of having law at all. Natural law asks that question first, not grudgingly.

To reason like a natural lawyer, you don’t discard positive law. You stop pretending that the statute book is the only map worth checking and ask one deceptively simple question:

If an act creates oppression but follows procedure, does it bind a judge’s conscience?

That’s the heart of the matter.

What Natural Law Theory Actually Claims (And What It Doesn’t)

There is no single natural law doctrine. Catholic writers, Kantians, contractarians and even some analytical folks have all held a version of this thought: unjust law is not true law in the most meaningful sense, and legal reasoning must include that background truth.

The modern realist of legal philosophy, John Finnis—who, wait for it, is also a professor of law and jurisprudence—distinguishes between the central case of law and its corrupt examples. A statute book utterly disconnected from human flourishing is like a “law” written by a tyrant to destroy the family. It has the external markers. It lacks the inner point.

That point, in classical natural law, is the common good. And by “good” you don’t need God to play the role—you only need to accept that humans have objective goods worth protecting: life, knowledge, friendship, practical reasonableness, aesthetic experience, and religion in a broad civic sense. Finnis calls these the basic forms of human flourishing.

Look, you don’t have to become Finnis. But if you want rational legal analysis that doesn’t reduce law to a slot machine, you need a framework that takes these goods seriously.

So let’s build you one.

A Step-by-Step Method for Natural-Law-Sensitive Rational Analysis

Start with a clean piece of paper in your head. Throw out the word “natural” for a moment—it makes lawyers twitch. Replace it with “ordinal purpose.”

Here’s the method, in four moves, no metaphysics required.

Move 1: Identify the Normative Commitments Inside Your Own Argument

Before you reason about whether a law is unjust, you should know what your legal language is already smuggling in. Every tool in the doctrinal toolkit has a moral weight.

Take the presumption of statutory meaning. Courts usually say, “We start with the plain text.” Why? Because of values like fairness, notice, separation of powers and predictability. Those are normative commitments—not cold clockwork.

Try it on a case about a tenancy eviction where the written lease gives the landlord the right to terminate “upon any breach” of a zoning clause by the tenant. The landlord wants to evict because the tenant once had a yard sale that violated a technically dormant ordinance. The judge looks at you and says, “The plain text is ‘any breach.’” But your instinct says enforcing the eviction here would be absurd, petty bad faith. Do you throw the instinct away? No—you unearth the normative commitments: the purpose of lease enforcement is to secure performance, not to punish contrived noncompliance.

Then you launch the second move.

Move 2: Name the Human Good at Stake (And Watch How the Law Already Protects It)

You don’t have to give a sermon on the divine architect. In rational practice, you name a concrete human good that the legal institution is meant to serve.

• In contract law, the good is mutually beneficial cooperation and reliance.
• In criminal law, the good is safety, dignity and restoration.
• In property law, the good is stable use, stewardship and home.

Notice what happened: you haven’t imported an external religious principle. You’re just being honest that law has a purpose. And to reason rationally, you need to articulate that purpose with precision.

Ask yourself: What human practice does this rule support? If enforcing a rule would undermine the very practice that gives it sense, that’s a natural-law argument. Courts call it “the absurdity doctrine” or “the presumption against unjust consequences.” Same animal, less intimidating outfit.

The Stanford Encyclopedia of Philosophy has a comprehensive overview of natural law theories that outlines these teleological foundations better than any one bar prep course ¹. What matters for your reasoning is that this account of purpose has nothing to do with religious dogma and everything to do with whether law is intelligible.

Move 3: Apply the Test of Practical Reasonableness

Finnis again, but don’t run away. He gives us a brilliant rational test: no human basic good should be arbitrarily excluded, and no practical principle should be merely instrumentalized. In plainer language:

• Does this law treat a human being as an object rather than as an actor capable of community?
• Does it single out a class for burden without a proportionate basis?
• Does it destroy any of the basic goods—like family integrity or freedom from being deceived—rather than merely regulate their coexistence?

Here’s a quick example from corporate law: judicial review of shareholder oppression. The “good” of a corporation is not to maximize profit at any cost—even Delaware’s doctrinal metaphors pretend the shareholders are principals, not prey. A court that throws out a merger that leaves minority shareholders with literal pennies does not do so by invoking heaven. It weighs purposes.

You can see the same in family law: courts protect custody decisions that serve the “best interests of the child.” Do you hear how much of that doctrine is natural law in street clothes? Absolutely.

By the way, notice one important discipline of this move: you cannot use natural law to justify any outcome you happen to like. The test is reciprocal. It forbids the tyranny of your own convenience as much as the legislature’s. Put another way—if you would not allow a judge to void a law just because she dislikes handguns, you also should not allow a judge to void a law because she imagines a cosmic rule hidden behind the clouds.

Practical reasonableness demands coherence. That’s its strength.

Move 4: Translate Your Natural Law Intuition Into the Institution’s Doctrine

Most judges get nervous if you mention Aquinas in a reply brief—doubly so in a footnote. Not because they’ve studied and rejected that man, but because they don’t want the opinion overturned on review. So your job is translation. Use doctrine as the vehicle; purpose as the engine.

Concrete move list:

• Attack the legislative history of purpose where proffered.
• Use canons of construction that defeat absurd results, like ejusdem generis or the presumption against violations of international law.
• Quote the statute’s findings of fact. Legislative findings are often disguised natural law arguments.
• In constitutional cases, invoke the traditions of ordered liberty or the due-process prohibition on outrageous state action.

Then watch what the other side does. They will say you’re legislating from the bench. Your answer: we are not. We are choosing the reading that keeps a human institution moored to its reason for existing. If that sounds soft, invoke James Madison: government is the greatest of all reflections on human nature, but “If men were angels, no government would be necessary” ². Even the dry pragmatist agrees that law’s premises about human fallibility and enterprise are morally loaded.

The Table: Three Jurisprudential Styles and Their Central Questions

To sharpen your rational legal analysis, it helps to map the field. Use this comparison when you’re trying to figure out which voice a judge is writing in:

The table below is worth keeping next to your desk:

Understand the table, and you become dangerous in the best way. You can shift registers.

First-year students treat those columns as warring parties. In practice, they are layers. The efficient legal analyst checks positive law first—then tests result patterns—then, before writing a single sentence, checks sense.

The difference between a hack and a good lawyer is the last check.

Common Objections (And Why They Aren’t the Hit You Think They Are)

“That’s just the naturalistic fallacy!”

Ah, Hume’s old saber. You cannot derive an “ought” from an “is”—we all know it. Natural law theory, at least in its sophisticated form, doesn’t try.

The claim is not “human nature is X, therefore everyone ought to do Y.” The claim is that law—a promise to coordinate human action through reason—has evaluative criteria built into its very concept. Compare it to a “knife.” If someone hands you a slab of rubber shaped like a blade, you don’t just say, “Well, that’s an unusual knife.” You say it’s a bad knife, or even no knife at all, because the point of a knife is cutting.

You haven’t committed a fallacy. You’ve reasoned evaluatively about a social artifact.

“If judges use natural law, tyrants use it too.”

This is the strongest objection, not the weakest. You’re right: in the mouths of ideologues, natural law can be a smokescreen for reaction, or a basis to declare “unconstitutional” anything that offends a particular sect.

But that is an argument for doing it better and more rationally, not an argument for pretending we don’t all have a deep intuition that a legal order built on torture or child abuse has a sickness that no chain of positive authorization can cure.

Think about the cosmopolitan human rights trials after the Second World War. Courts argued that certain acts were “so offensive to the conscience of humankind” that no statute of limitations, no state immunity, no command of the local Führer, could make them lawful. That reasoning has natural law written all over it—and it is one of the proudest moments of modern law.

“We already have rational utility tests.”

You’re thinking about cost-benefit analysis, law and economics. Good. But be careful: measuring efficiency does not answer whose good matters, nor does it weigh incommensurable values like respect and dignity. Natural law reasoning often does what a hand-wavy “we could optimize welfare” cannot do: it identifies non-negotiable limits on what legislatures may impose even when all sides admit that efficiency gains are large.

You can measure the social benefit of forced “confessions” very precisely. Yet you wouldn’t let the state do it. Notice what your body does before you rationalize away that yes? That’s a natural law intuition inside a trained mind. Trust but verify.

A Quick Practice Exercise (So You Don’t Just Nod and Leave)

Let’s do a 60-second drill. Imagine a city council passes an ordinance requiring all residential building owners to install a dangerous surveillance system, without warrants, and punish noncompliance with a fine of $5,000 per week. No judicial check, no basis for objection.

Run through the moves:

1. Move one: Identify normative language in the ordinance. You find the word “safety.”
2. Move two: Name the good. Human privacy, dignity and trust are also goods.
3. Move three: Test for rationality. Does balancing safety through blanket surveillance of private homes actually make citizens safer? Often yes, statistically—and crime does drop. But does the rule destroy another basic good in the process? Yes: you systematically destroy the sphere where family intimacy and friendship can exist.
4. Move four: Translate. You say: “The ordinance is arbitrary and disproportionate. It inflicts a burdensome scheme that fails to account for the purpose of ‘safety’ in community life, and is therefore beyond the police power, violating due process under the state constitution.”

Notice there’s no Bible in that paragraph, no “divine order,” and no name-calling. Just an argument about whether posited law aligns with the point of the institution. A rational legal analyst can receive that argument—and either accept it or beat it with evidence. That’s the kind of fight law was designed for.

Bring This Into Your Own Work Flow

So, practical checklist for the next time you draft an argument, write a bench memo or advise a client:

• Skim the statute for terms that encode moral judgments (“reasonable,” “public policy,” “good faith,” “conscience”). Those are entry points.
• Write two sentences: What is this rule trying to make flourish? and What would accepting it destroy?
• Keep the basic goods list on a sticky note: life, knowledge, play, aesthetic experience, sociability/community, practical reasonableness, and religion or transcendent concern of some form.
• Then translate the argument into precedent-friendly language.

If you want to go deeper into the theory without reading 800 pages of Latin, the Internet Encyclopedia of Philosophy offers a balanced introduction to natural law ethics and its modern defenders ³. Alternatively, pick up Lon Fuller’s The Morality of Law. Fuller, a pure procedural theorist, argued that even the devil’s legal system would fail to be law unless it respected internal principles of clarity, generality, publicity and non-contradiction. That is natural law as formalism—and it is neat enough to survive any positivist dinner party.

A Final Thought Before You Open the Memo

A good legal analyst cannot begin with a conclusion and work backwards. But neither should you pretend that law was invented as a value-free slot machine.

Every time you say “this is the right outcome,” you are doing natural law reasoning. The rational analyst just does it honestly, with the goods named, the test stated and the counterargument welcomed.

Consider this your invitation: don’t cede the language of purpose to people who want to weaponize it. Claim it for precision. It belongs to reason as much as to religiosity.

Now go write that memo. And if your partner scoffs at the “absurdity doctrine,” quote him Fuller and Finnis. Then make the winning argument anyway.