There have been very few papal resignations in the history of the Catholic Church. The last to do so was Pope Gregory XII, in 1415 as part of a deal to end the Great Western Schism in which two rivals had separately declared themselves pope. The dispute had threatened to tear the church apart.

Perhaps better known is the resignation of Celestine V in 1294, who had only been in the position for less than six months. The then 89-year-old Celestine had paved the way for himself to step down by issuing a decree that made it possible for a pope to resign.

His successor, Pope Boniface VII prevented his attempt to spend his final days in solitude, having him captured and holding him prisoner in a castle outside of Rome until his death 18 months later.

No clear rules for change of power

In the 20th century, three popes are reported to have written letters of resignation.

Pius XII, who was pope from 1939 to 1958, wrote his after the Nazi regime of Adolf Hitler came to power in Germany. Pius is reported to have signed a letter that stated that should he be kidnapped by the Nazis, he should be considered as having resigned his as pope.

In the cases of Pope Paul VI (1963-1978) and Pope John Paul II (1978-2005), there were concerns about the possibility of the church finding itself left with a pontiff who had become incapacitated due to failing health.

During the last few months of his life, there was considerable public speculation that John Paul II would step down. Such rumors were repeatedly rejected by the Vatican right up until his death in 2005.

Technically, a papal resignation leaves the church in the same state as it is after a pope has died: The post is vacant until a successor can be chosen. There are no precise rules as to how a new pope is to take over.

Under Canon 332 of the Code of Canon Law, the only conditions that need to be fulfilled for a pope to resign are that the decision be made freely and that it be manifested properly.

"If it happens that the Roman Pontiff resigns his office, it is required for validity that the resignation is made freely and properly manifested but not that it is accepted by anyone," states the new edition of Church Law, which was implemented in1983.

There is no clear provision for what is to be done if a pope becomes incapacitated while in office. According to Canon 335, this case is to be treated as if it were a vacncy, however it does not state who or on what basis would determine that the pope is "incapacitated."

pfd/mkg (epd, dpa, AP)