What is a writ of habeas corpus used for?

A writ of habeas corpus is a fundamental legal instrument used to protect individual freedom against unlawful detention. Specifically, it serves to bring a prisoner before a court or judge to determine whether their imprisonment is lawful. This legal safeguard ensures that no individual can be held in custody without just cause, allowing the court to assess the legality of the detention and to uphold the principle of due process.

In contrast, announcing a formal charge against a defendant pertains more to the charging documents necessary in criminal proceedings, which is a different legal process. Convicting criminals in absentia refers to trials conducted in the absence of the defendant, which is not related to habeas corpus. Granting clemency involves the reduction of a punishment or the granting of a pardon by a governing authority, again unrelated to the protective function of habeas corpus. The primary focus of a writ of habeas corpus is on the individual's right to not be unlawfully detained, making the correct answer the one that reflects this purpose.