Perjury, the crime of lying under oath, is a serious offense because it can derail the basic goal of the justice system—discovering the truth. Even the famous and the powerful have faced the consequences of perjury, which include prosecution, prison, and impeachment.

What Is Perjury?

“I swear to tell the truth, the whole truth, and nothing but the truth.” It’s an oath so familiar that its significance can be overlooked. But, when sworn in a court or other official proceeding, it makes everything said afterward either the truth or perjury.

Historically, perjury was defined as lying while testifying in court. The law now defines the crime to cover not just trials but also many other proceedings, including grand juries, family law court, bail hearings, Congressional committee hearings, and depositions in civil lawsuits. Sworn statements made to governmental agencies such as the Social Security Administration or in financial affidavits (such as loan applications) are also covered.

It’s also a criminal offense to cause another to commit perjury, called suborning perjury.

How Is Perjury Proven in Court?

To convict on perjury charges, a prosecutor must prove a person knowingly made a false statement of material fact under oath. All parts of this definition are important, so let’s take a closer look at each and some examples of perjury.

Statement Made Under Oath or Affirmation

Perjury can take the form of oral or written statements made under oath or affirmation. For instance, a witness giving testimony at trial makes an oral statement under oath. Statements made outside of court can also be subject to perjury charges. For instance, a person might provide testimony under oath at a deposition or Congressional hearing. Someone who intentionally lies about their assets on a written loan application may also sign under penalty of perjury.

Knowingly Give a False Statement

The witness must know that the testimony is false. False testimony that results from confusion, memory lapse, or mistake is not perjury. Conflicts in testimony may be perjury if one of the conflicting statements is necessarily false. (In such a case, prosecutors can prove perjury without proving which one is false).

Let’s say one witness testifies the get-away car was black but another witness says blue. Neither has committed perjury if their memories are simply unclear. But if one of those witnesses purposely states the wrong color in hopes to mislead the jury, that witness commits perjury.

Statement Must Be Material to the Proceeding or Issue in Question

The false statement must be capable of influencing the proceeding or issue in question—that is, it must have a relationship to whatever issue is being decided. A lie, even under oath, about a subject that is not material to the proceeding is not perjury. For example, falsely bragging that “I never update my Instagram page at work,” while testifying in a case having nothing to do with social networking at work, would not be a likely candidate for a perjury charge.

What Is the Punishment for Perjury?

A person convicted of perjury under federal law may face up to five years in prison and fines. (18 U.S.C. § 1621.) The punishment for perjury under state law varies from state to state but is typically a felony. Felonies carry a possible prison sentence of at least one year, plus fines and probation.

If a witness commits perjury in an attempt to hide or assist another in a crime, the prosecutor might skip the perjury charges and file charges for conspiracy or aiding and abetting a crime. This situation might occur if these charges carry a greater penalty than perjury.