Yes, a pope can resign. The number popes who may have resigned has been estimated as high as 10, but the historical evidence is limited. Most recently, during the Council of Constance in the 15th century, the Gregory XII resigned to bring about the end of the Western Schism and a new pope was elected in 1417. Pope Celestine V’s resignation in 1294 is the most famous because Dante placed him in hell for it.
Most modern popes have felt that resignation is unacceptable. As Paul VI said, paternity cannot be resigned. In addition, Paul feared setting a precedent that would encourage factions in the church to pressure future popes to resign for reasons other than health. Nevertheless, the code of canon law in 1917 provided for the resignation of a pope as do the regulations established by Paul VI in 1975 and John Paul II in 1996. However, a resignation induced through fear or fraud would be invalid. In addition, canonists argue that a person resigning from an office must be of sound mind (canon 187).
In 1989 and in 1994, John Paul II secretly prepared letters offering the College of Cardinals his resignation in case of an incurable disease or other condition that would prevent him from fulfilling his ministry, according to Msgr. Slawomir Oder, postulator of the late pope’s cause.
Catholic News Service reports:
The 1989 letter was brief and to the point; it says that in the case of an incurable illness that prevents him from “sufficiently carrying out the functions of my apostolic ministry” or because of some other serious and prolonged impediment, “I renounce my sacred and canonical office, both as bishop of Rome as well as head of the holy Catholic Church.”
In his 1994 letter the pope said he had spent years wondering whether a pope should resign at age 75, the normal retirement age for bishops. He also said that, two years earlier, when he thought he might have a malignant colon tumor, he thought God had already decided for him.
Then, he said, he decided to follow the example of Pope Paul VI who, in 1965, concluded that a pope “could not resign the apostolic mandate except in the presence of an incurable illness or an impediment that would prevent the exercise of the functions of the successor of Peter.”
“Outside of these hypotheses, I feel a serious obligation of conscience to continue to fulfill the task to which Christ the Lord has called me as long as, in the mysterious plan of his providence, he desires,” the letter said.
Historical evidence for papal resignations is limited, especially if one eliminates resignations that may have been forced.
1. Clement I (92?-101). Epiphanius asserted that Clement gave up the pontificate to Linus for the sake of peace and became pope again after the death of Cletus.
2. Pontian (230-235). Allegedly resigned after being exiled to the mines of Sardinia during persecution of Maximinus Thrax.
3. Cyriacus. A fictional character created in the Middle Ages who supposedly received a heavenly command to resign.
4. Marcellinus (296-304). Abdicated or was deposed after complying with Diocletian’s order to offer sacrifice to pagan gods.
5. Martin I (649-655). Exiled by Emperor Constans II to Crimea. Before he died, clergy of Rome elected a successor whom he appears to have approved.
6. Benedict V (964). After one month in office, he accepted deposition by Emperor Otto I.
7. Benedict IX (1032-45). Benedict resigned after selling the papacy to his godfather Gregory VI.
8. Gregory VI (1045-46). Deposed for simony by Henry III.
9. Celestine V (1294). A hermit, elected at age of 80 and overwhelmed by the office, resigned. He was imprisoned by his successor.
10. Gregory XII (1406-15). Resigned at request of Council of Constance to help end the Great Western Schism.
Source: Patrick Granfield, “Papal Resignation” (The Jurist, winter and spring 1978) and J. N. D. Kelly, The Oxford Dictionary of Popes (1986).
In Light of the World, Pope Benedict responded unambiguously to a question about whether a pope could resign: “Yes. If a Pope clearly realizes that he is no longer physically, psychologically, and spiritually capable of handling the duties of his office, then he has a right and, under some circumstances, also an obligation to resign.”
On the other hand, he did not favor resignation simply because the burden of the papacy is great. “When the danger is great one must not run away. For that reason, now is certainly not the time to resign. Precisely at a time like this one must stand fast and endure the situation. That is my view. One can resign at a peaceful moment or when one simply cannot go on. But one must not run away from danger and say someone else should do it.”