What Is Perjury? Lying Under Oath and Why Courts Punish It

Perjury in English law, under the Perjury Act 1911, is committed by a person lawfully sworn as a witness in a judicial proceeding who wilfully makes a statement material to the proceeding that they know to be false or do not believe to be true. Each part matters. The person must have taken an oath or affirmation; the statement must be in a court or tribunal, or in a sworn document such as an affidavit; it must be material, bearing on the case, so that a lie about an irrelevant detail is not perjury; and it must be knowing, so that a witness who is honestly mistaken, however badly, has committed no crime. The American federal offence is the same in substance, and both extend to written statements made under penalty of perjury, which is how a false tax return or a false declaration on a form becomes the crime.

The oath is what makes a lie perjury, and its history is the history of the courts' attempts to make people tell the truth. Medieval witnesses swore on the Gospels and were believed to risk damnation; the Quakers, who refused to swear because Jesus had forbidden it, won the right to affirm instead in 1695, and an affirmation, a solemn promise without religious content, has had the same legal force as an oath since 1888. The words in an English court are to tell the truth, the whole truth and nothing but the truth, and the oath's practical purpose today is not to frighten the witness with God but to fix the moment from which a lie becomes a crime and to remind the witness that it does. The elements a prosecutor must prove:

• •That the defendant was sworn or affirmed, in a proceeding that the law covers
• •That they made the statement alleged, which requires a transcript or a written declaration
• •That the statement was false in fact
• •That it was material to the proceeding
• •That the defendant knew it was false or did not believe it true, which is the element that defeats most cases, and which in England must be supported by more than one witness's word

Witnesses lie in court every day and almost none are charged, because proving that a person knew a statement was false is hard, because the lie is usually exposed only by the court's disbelieving it, which is not proof, and because a prosecution after a trial reopens the trial. The cases that are brought are the ones where the falsity is documented: the alibi contradicted by phone records, the sworn financial statement contradicted by the bank, the witness who admits the lie. Perjury is charged most often against people who were not the main defendants, the friend who gave the false alibi, the spouse who took the speeding points, and against the powerful when the lie is the story; Jonathan Aitken and Jeffrey Archer went to prison in Britain for perjury in libel actions they had brought themselves, and Bill Clinton's impeachment in 1998 was for perjury about an affair in a civil deposition, of which the Senate acquitted him.

Perjury is one of a family. Perverting the course of justice, in England, is the broader common-law offence of interfering with an investigation or trial by any means, from destroying evidence to intimidating a witness, and it carries life imprisonment; it is the charge used when the oath was not taken, as when a person lies to the police. Contempt of court covers lies and disobedience in the face of the court. Subornation of perjury is procuring another person to commit it, and false statements to officials, the American offence under which many high-profile prosecutions proceed, requires no oath at all. Together they say that the legal system's raw material is testimony, and that corrupting it is treated as an attack on the system rather than a wrong to a party.

The oath binds the accused too, if they choose to testify, and the choice is a hard one. A defendant who gives evidence and is disbelieved has, in principle, perjured themselves in addition to the offence charged, though prosecutions for that are vanishingly rare, since every convicted person who testified would otherwise face a second charge. The right to silence exists partly for that reason. In the United States the Fifth Amendment lets a witness refuse to answer any question whose truthful answer would incriminate them, and taking the Fifth is the lawful alternative to the lie; a witness who chooses instead to answer, and to answer falsely, has chosen the crime that the system reserves for those who break the one promise on which it runs.

Perjury is the crime of making, under oath or affirmation in a judicial proceeding or a sworn document, a statement that is material to the matter and that the maker knows to be false; honest mistakes and irrelevant lies do not count, and the knowledge element makes it hard to prove, so that it is charged mostly where documents expose the lie. It carries up to seven years in England and five in America, sits alongside perverting the course of justice and contempt, and exists because testimony is what courts are made of.