Law schools and courts divide the law into fields. One of the oldest divisions, going back to Roman law, is between public law and private law. It helps you guess who the parties will be and what kind of rules apply. It builds on the sources of law.
Key idea
Public law governs the relation between the government and people: constitutional, administrative and criminal law. Private law governs relations among people and organizations: contracts, torts, property, family law and business law.
| Public law | What it covers | Private law | What it covers |
|---|---|---|---|
| Constitutional law | the structure of government and the rights it must respect | Contracts | enforceable promises |
| Administrative law | how agencies make rules and decisions | Torts | civil wrongs that cause harm, such as negligence |
| Criminal law | offenses against the public, prosecuted by the government | Property | ownership and use of land and things |
| Tax law | what people owe the government | Family law | marriage, divorce, custody, adoption |
Why it works
The line follows whose interest is at stake and who may bring the case. In public law, the government acts as the government: it prosecutes, regulates or taxes, and it is limited by the Constitution. In private law, the government acts as a referee: its courts settle disputes between private parties, and the injured party decides whether to sue. That is why a crime is prosecuted by "the State" or "the People" even though one person was harmed: the law treats a crime as a wrong against the whole community.
Worked example: One event, two fields
Dana shoves Lee in a parking lot and breaks Lee's glasses. Which body of law applies?
- Criminal law (public): the state may charge Dana with assault or battery. The prosecutor decides, not Lee.
- Tort law (private): Lee may sue Dana for battery to get money for the glasses and any injury.
- The two cases are separate, with different parties and different rules.
Answer: Both: a public criminal case (State v. Dana) and a private tort suit (Lee v. Dana).
Worked example: The government as a private party
A city signs a contract to buy fire trucks and then refuses to pay. Public or private law?
- The dispute is over a contract, a private-law subject.
- The city is acting much like any buyer, so contract law mostly governs, though special rules may apply to suits against governments.
Answer: Mainly private law (contracts), even though a government is a party.
Common mistake
Placing criminal law in private law because a person was harmed. A crime is an offense against the public, prosecuted by the government; the victim does not control the case and cannot drop the charges. The victim's own claim for money is a separate, private case. Check: who is the party bringing the case? If it is the government enforcing a criminal law, it is public law.
This is an educational course, not legal advice.