PARIS Pope Benedict would not be the meticulous theologian he has always been if he didn't make sure even his shocking resignation - the first by a pontiff in over 700 years - was fully in line with Roman Catholic doctrine.
His announcement was so stunning that many Catholics will have instinctively asked if a pope is allowed to step down. For many of them, Pope John Paul's long and very public agony before he died in 2005 is the iconic image of the end of a papacy.
But the Code of Canon Law, the legal corpus governing the Church, clearly provides for a papal resignation in its Canon 332. John Paul mentioned it in a detailed 1996 document that laid down the procedure for electing a new pope.
Benedict's reputation as an orthodox and self-effacing pope ensures there will be few questions about the legality of the move and will reduce speculation that he plans to continue to play a decisive role behind the scenes.
"This is a very surprising move from a very traditional pope," said Christopher Bellitto, a Church historian at Kean University in New Jersey. "It's quite heroic."
Benedict's deep respect for the papacy insures he will avoid the problems that could arise, he said: "He's a company man - he's not going to do anything to harm the institution."
By citing health reasons for his decision, Benedict has also helped the Church by setting a modern precedent for resigning at a time when medical progress means the elderly can live far beyond their active years.
"There will be more and more medical issues, like what to do if a pope is incapacitated, and this will make it easier for future popes to resign," Bellitto said.
THE EMPTY SEAT
The main threat to the papacy that a retired pope poses is what the Church calls "sedevacantism," or the belief that the new pope is not the valid pontiff and the See of Saint Peter - the papal throne - is actually vacant.
A tiny group of ultra-conservative Catholics say the papacy has actually been vacant since the death of Pius XII in 1958 because his successor, John XXIII, called the Second Vatican Council (1962-1965) that brought in sweeping reforms.
Any statement or action by a former pope could give arguments to supporters of this theory, which is one reason why Benedict will live in a cloistered convent inside the Vatican walls and probably appear rarely if ever in public.
"Inevitably there will be a group that follows him and sets up a website about it," Bellitto said. But Benedict, who wanted to retire to write books even before John Paul died, will probably turn down any request to speak in public.
"He'll probably lead the kind of life he expected to lead before he became pope," the historian added.
While Benedict is the first pope to resign since Celestine V in 1294, he is far from being the first to consider it.
John Paul prepared letters of resignation in 1989 and 1994 in case he was incapacitated. Pius XII is believed to have done the same during the Second World War in case he was captured by the Nazis, but his archives have not yet been opened to confirm this.
AUTHORITY ANOTHER ISSUE
Another issue is whether a retired pope would retain the spiritual authority he had while in office. One might assume this because a retired bishop remains a bishop in the eyes of the Church, even without his administrative authority.
But the Catholic priesthood has only three ministerial orders - bishop, priest and deacon. The posts above them, such as archbishop, cardinal and pope, are Church offices.
So on his resignation, Benedict will lose not only the office of pope but also several titles that go with it including Vicar of Jesus Christ, Bishop of Rome, Sovereign of the Vatican City State and Servant of the Servants of God.
"If he resigns the office, he no longer has the authority of Saint Peter de facto," said Bellitto.
The link to Saint Peter is essential because he was the first pope, chosen by Jesus, and the Church traces its hierarchy back to his authority being passed down through the centuries to the present pope and bishops.
The Vatican has a detailed plan for dealing with a papal interregnum. In the absence of a pope, the College of Cardinals, made up of the senior-most prelates, runs the daily government of the Church and organizes the closed-door conclave to elect the next pope, but cannot make major policy decisions.
The Vatican said the new pope should be in office before Easter, which falls on March 31 this year, but has not given any further details.
Under the rules from 1996, a conclave must start between 15 and 20 days after the death of a pope. However, that includes nine days for mourning and a funeral. If the Vatican subtracts the mourning and funeral period, the conclave could start between six and 11 days after Benedict resigns on Feb 28.
(Reporting By Tom Heneghan; Editing by Peter Graff)