The call to the bar is a legal term of art in most common law jurisdictions where persons must be qualified to be allowed to argue in court on behalf of another party and are then said to have been "called to the bar" or to have received "call to the bar". "The bar" is now used as a collective noun for barristers, but literally referred to the wooden barrier in old courtrooms, which separated the often crowded public area at the rear from the space near the judges reserved for those having business with the court. Barristers would sit or stand immediately behind it, facing the judge, and could use it as a table for their briefs.
Like many other common law terms, the term originated in England in the Middle Ages, and the call to the bar refers to the summons issued to one found fit to speak at the "bar" of the royal courts. In time, English judges allowed only legally qualified men to address them on the law and later delegated the qualification and admission of barristers to the four Inns of Court. Once an inn calls one of its members to its bar, they are thereafter a barrister. They may not, however, practise as a barrister until they have completed (or been exempted from) an apprenticeship called pupillage. After completing pupillage, they are considered to be a practising barrister with a right of audience before all courts.
