The rule of priestly celibacy has been called into question by Pope Francis, who says he believes that the rules requiring all priests to abstain from sex "can be changed."

The newly-appointed pope's views have come to light in a Spanish language book entitled Sobre el Cielo y la Tierra (On the Heavens and the Earth).

Francis's views on celibacy may be based on his own personal experiences. He has spoken about his early years in a seminary when he was "dazzled by a girl I met at an uncle's wedding."

"I was surprised by her beauty, her intellectual brilliance ... and, well, I was bowled over for quite a while. I kept thinking and thinking about her. When I returned to the seminary after the wedding, I could not pray for over a week because when I tried to do so, the girl appeared in my head. I had to rethink what I was doing."

In the journal, the pope spoke to Rabbi Abraham Skorka in the days before he was elected to the papacy and known as Cardinal Jorge Bergoglio. The English version of the book-length dialogue with the rabbi will be published in May.

Pope Francis says he eventually decided to stay in the priesthood and adhered to the rule of celibacy.

However, he went on to commend priests in other faiths such as the Byzantine, Ukrainian, Russian or Greek Catholic Church, who are allowed to marry.

"They are very good priests," he noted. "If, hypothetically, Western Catholicism were to review the issue of celibacy, I think it would do so for cultural reasons [as in the East], not so much as a universal option."

Nevertheless, the pope's views on changing the Catholic Church's rules on celibacy remain very much a theoretical debate.

"For the moment, I am in favour of maintaining celibacy, with all its pros and cons, because we have ten centuries of good experiences rather than failures," Francis said.

"What happens is that the scandals have an immediate impact. Tradition has weight and validity. Catholic ministers chose celibacy little by little. Up until 1100, some chose it and some did not. After, the East followed the tradition of non-celibacy as personal choice, while the West went the opposite way. It is a matter of discipline, not of faith. It can change."

The first-ever Argentine pope's views have raised eyebrows from some quarters. Thomas Reese, of the National Catholic Reporter, said that the papal leader's comments were surprising because "'For the moment' and 'for now' are not the kind of qualifications one normally hears when bishops and cardinals discuss celibacy."

The tradition in the Catholic Church has been for priests as well as bishops to take vows of celibacy, a rule that has been in place since the early Middle Ages.

The Catechism of the Catholic Church states: "All the ordained ministers of the Latin Church, with the exception of permanent deacons, are normally chosen from among men of faith who live a celibate life and who intend to remain celibate "for the sake of the kingdom of heaven."

Psychotherapist and former Benedictine priest Richard Sipe has conducted a study of celibate and sexual behaviour among Catholic clerics in the United States from 1960 to 1985, and found that half of all priests and Catholic brothers were sexually active at any particular time.

Masturbation was the most frequent sexual activity, followed by affairs with women, sex with male companions, and Internet pornography. He also believes that these numbers have not changed much today.

"Sex is really very close to an addiction. It's a drive that doesn't go away," Sipe told the New York Times. "If you're going to live without it, you can't live like a normal person. You can't just say one day, 'I'm celibate.' Celibacy is a process."

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