During the canonisation process, the promoter of the faith, popularly known as the devil’s advocate, was a canon lawyer appointed by church authorities to argue against the canonisation of a candidate. It was this person’s job to take a sceptical view of the candidate’s character, to look for holes in the evidence, to argue that any miracles attributed to the candidate were fraudulent and so on. The devil’s advocate opposed God’s advocate (in Latin, advocatus Dei, also known as the promoter of the cause), whose task was to make the argument in favour of canonisation. The first formal mention of such an officer is found in the canonisation of St Lawrence Justinian under Pope Leo X (1513–1521), the first office was established in 1587 during the reign of Pope Sixtus V. In 1983, Pope John Paul II reduced the power and changed the role of the office.
Today, in common language, the phrase “playing devil’s advocate” describes a situation where someone, given a certain point of view, takes a position they do not necessarily agree with (or simply an alternative position from the accepted norm) for the sake of debate or to explore the thought further using valid reasoning that both disagrees with the subject at hand and proves their own point valid.