Note: I do not use Grok or AI to cheat or write for me, but only as a tool for research and assistance, summaries, and so on. Here is the summary of a Grok discussion I had trying to clarify some issues, so asked it to prepare the summary in the form of a blog post.
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A few days ago at the Libertarian National Committee event (LNC 2026) in https://www.lnc2026.com/, I was having a lively discussion with two fellow libertarian lawyers. The conversation started with a practical question: Could the Libertarian Party amend its bylaws to prohibit certain behaviors, and would applying those new prohibitions to past actions (or ongoing situations) potentially violate ex post facto principles?
That initial discussion about internal party rules and fairness quickly evolved into a much deeper exploration of U.S. constitutional law, common law crimes, the Ex Post Facto Clause, historical legal development, and broader libertarian theory about legislation, malum in se vs. malum prohibitum offenses, and anarcho-capitalist systems. One of my friends brought up the Ex Post Facto Clause and argued that it effectively requires all crimes (or prohibitions) to be created by clear, prospective legislation or rules. He believed allowing non-statutory or judge-made rules would violate constitutional protections against retroactive punishment. He thought pure common law crimes only really existed in pre-U.S. England, and that modern American law had moved past that.
He was wrong on the strict constitutional point, but his instincts were largely right—especially from a consistent libertarian perspective. Here’s a detailed, comprehensive recap of the full conversation.
The Starting Point: Libertarian Party Bylaws and Ex Post Facto Concerns
We began by debating whether a private organization like the LP could amend its bylaws to add new prohibitions and enforce them against members for prior conduct. This raised natural questions about fairness, notice, and retroactivity—concepts that mirror the Ex Post Facto Clause in the U.S. Constitution. From there, we moved into how these ideas apply in actual state criminal law.
The Constitutional Framework: Ex Post Facto and Due Process
The Ex Post Facto Clause (U.S. Constitution, Article I, Section 9, applied to the states via the Fourteenth Amendment) prohibits government laws that criminalize conduct after it has occurred or that retroactively increase punishment. However, this clause does not require every crime to be defined by a legislative statute.
It is constitutionally permissible for a state to enforce longstanding common law crimes—offenses developed through judicial precedent rather than statutes—as long as the conduct was clearly recognized as criminal under established common law at the time it occurred.
Current Real-World Example: North Carolina
A strong modern example is North Carolina, which still recognizes and actively enforces several common law crimes not fully defined by statute. These include:
- Common law obstruction of justice (actions that prevent, obstruct, impede, or hinder public or legal justice; can be misdemeanor or felony).
- Common law robbery.
- Affray (fighting in public that disturbs the peace).
- Going armed to the terror of the people.
North Carolina’s General Statutes explicitly receive the common law of England as it existed in 1776, unless modified or repealed by statute. Courts apply these based on case law. Other states like Maryland retain some common law offenses as well.
This proves it is not unconstitutional for a state to punish certain crimes without a specific legislative statute defining every element.
Key limit: If a court announced an entirely new crime never before recognized and applied it to the defendant, that would violate the Due Process Clause (fair notice requirement). Defining brand-new offenses on the fly fails the principle of legality and raises separation-of-powers issues.
Historical Development: How Common Law Crimes Evolved
We briefly touched on The Paquete Habana (1900) as an entry point into international/customary law, but the core discussion focused on common law evolution.
In early English common law, there was no ex post facto prohibition like ours. Courts extended general principles gradually to new situations involving conduct widely understood as inherently wrongful. They did not typically invent brand-new crimes in single decisions.
The classic felonies (murder, rape, robbery, arson, theft) are malum in se — wrong in themselves, natural rights violations (aggression against person or property) recognized across time and cultures. Reasonable people have always known these were wrongful.
This contrasts with malum prohibitum offenses (wrong only because a statute or rule says so), such as most regulatory crimes. These demand clear, advance notice.
The Libertarian Takeaway
As libertarians who generally oppose legislation and favor minimal or stateless systems:
- We don’t actually need statutes (or detailed bylaws) to define legitimate rules against aggression. The core prohibitions were already recognized in the common law tradition.
- True crimes are malum in se violations of person and property. Expansive rules created via legislation or after-the-fact amendments are often problematic.
- In a pure anarcho-capitalist society (no state, no legislation, private law and arbitration), the concept of “ex post facto law” would largely disappear. Private courts would apply natural law principles focused on restitution. There would be no central body capable of suddenly inventing new prohibitions.
Regarding the original LP bylaws question: Private organizations have more flexibility than governments, but principles of fair notice and avoiding retroactive punishment remain good practices for voluntary associations.
Why My Friend’s Instincts Were Right
My friend correctly sensed the danger of retroactive rules and the importance of predictability. In a mature system, we should avoid both legislative overreach and novel judicial inventions. Most states have shifted to comprehensive statutory criminal codes for this reason.
His error was assuming the Constitution mandates full statutory codification. It doesn’t — but strong libertarian principles and modern practice both favor clear, prospective rules, especially beyond the ancient malum in se core.
This discussion at LNC 2026 helped clarify an important nuance for libertarians: the Constitution allows more flexibility for historical common law than many assume, yet our philosophy pushes us toward minimizing coercive rule-making of any kind, whether by legislatures, judges, or even party bylaws.
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From Alessandro Fusillo:
Common sense principles like the “prohibition of ex post facto laws” often trace back to ancient Roman law. The origin of this principle, enshrined in the US Constitution, can be found in Ulpian:
D 50.16.131, Ulpianus, libro tertio ad legem Iuliam et Papiam, De verborum significatione: “No penalty shall be imposed except that which is specifically prescribed for a given offence by some law or other legal provision.” (“Poena non irrogatur, nisi quae quaque lege vel quo alio iure specialiter huic delicto imposita est”).
The reference to “other legal provision” mirrors the rationale underlying common law crimes: criminal conduct may be punishable even without a specific statute expressly defining it as such, provided it violates well-established legal principles.
This also carries a deeper implication: legislators are not above the law. A statute that formally permits conduct which nevertheless violates fundamental legal principles does not shield that conduct from criminal liability — legality on paper is not always legality in substance.
