A state has enormous power: it can arrest, imprison and take property. Due process is the principle that government must follow fair, established procedures before depriving a person of life, liberty or property. These procedures protect the innocent, and they protect everyone from officials who might otherwise act on suspicion, prejudice or convenience.

Roots

Magna Carta (1215) promised that no free man would be imprisoned or punished except by the lawful judgment of his peers or by the law of the land. An English statute of 1354 used the phrase “due process of law,” and the idea passed into many later constitutions. In the US, for example, the Fifth and Fourteenth Amendments forbid depriving any person of life, liberty or property without due process of law.

Habeas corpus

The Latin phrase habeas corpus means “you shall have the body.” It names a court order requiring those holding a person to bring the prisoner before a court and show lawful grounds for the detention. If they cannot, the prisoner must be released. England strengthened the remedy in the Habeas Corpus Act of 1679. The writ is sometimes called the great writ of liberty, because without it every other right can be defeated by simply locking a person away. Governments have occasionally suspended it in wartime or rebellion, and such suspensions are always controversial.

The presumption of innocence

The presumption of innocence means that the prosecution must prove guilt; the accused does not have to prove innocence. It is protected in the Universal Declaration of Human Rights (1948) and in most constitutions. The English jurist William Blackstone, in the 1760s, gave it a famous moral arithmetic: “it is better that ten guilty persons escape, than that one innocent suffer.” The principle accepts that some guilty people will go free in order to protect the innocent from the far worse error of wrongful punishment.

Elements of a fair trial

International human rights treaties, such as the International Covenant on Civil and Political Rights (1966), list rights that most legal systems recognize in some form:

• to be told promptly, in a language one understands, what one is charged with;
• to have adequate time and means to prepare a defense, and to have a lawyer, provided free if one cannot pay and justice requires it;
• to examine the witnesses against oneself, and to have an interpreter if needed;
• not to be compelled to testify against oneself or confess guilt;
• to a public hearing, within a reasonable time, before an independent and impartial tribunal.

Two further principles are ancient. No crime without law (in Latin, nullum crimen sine lege) means that no one may be punished for an act that was not a crime when it was committed. Protection against double jeopardy means that a person finally acquitted or convicted cannot be tried again for the same offense, though some countries allow narrow exceptions, such as compelling new evidence.

US example. In Gideon v. Wainwright (1963), the Supreme Court held that states must provide a lawyer to defendants charged with serious crimes who cannot afford one. Clarence Gideon had written his petition by hand from prison; at his retrial, with a lawyer, he was acquitted.

Rights under pressure

Due process can feel like an obstacle when the public is frightened or a crime is shocking. Its defenders answer that the procedures exist precisely for those moments, since a rule that protects only popular defendants protects no one. The hard questions, such as how long a suspect may be held during a terrorism investigation, are about how to keep these protections meaningful under strain.

Worked example: held without charge

In an invented country, police detain a university student, Ilan, after a protest. Three days pass. He has not been charged, he has not seen a lawyer, and his family does not know where he is. What do the principles of this level require?

1. Habeas corpus. Ilan's family, or a lawyer acting for him, can ask a court for a writ. The court orders the police to produce Ilan and explain the legal basis for holding him. If they have none, he must be released.
2. Notice of charges. If the police do have grounds, Ilan must be told promptly, in a language he understands, what he is accused of.
3. A lawyer. He has a right to legal help to prepare his defense, provided free if he cannot pay and the charges are serious.
4. No forced confession. He cannot be compelled to testify against himself. A confession extracted after days of isolation would be suspect and, in many systems, inadmissible.
5. Presumption of innocence. At trial the prosecution must prove that he committed a specific offense. He does not have to prove that he did not.
6. No crime without law. If the police claim he broke a protest rule announced the day after the protest, that rule cannot be used to punish him.

None of these steps decides whether Ilan is guilty. They decide how the question will be answered: openly, before an impartial court, with a fair chance to respond. That is the whole point of due process.