Pope Francis on Monday opened the most highly anticipated meeting of Catholic Church leaders since the Second Vatican Council half a century ago, saying they should air their differences on controversial issues.
"As I said, the synod is not a parliament where, in order to reach a consensus or a common accord we resort to negotiation, pacts or compromise," Francis said.
He urged delegates at the synod to "courageously engage in pharresia" - meaning open, frank debate - and warned them against political bargaining
He was addressing around 270 Church leaders gathered at the Vatican for the three-week summit likely to be dominated by the fraught issues of divorce and homosexuality.
The most divisive issue at stake at the meeting is whether to drop a longstanding ban on divorcees who remarry taking communion.
Several cardinals on both sides of the debate have warned that the Catholic Church risks a schism over the controversy.
Other flashpoint issues include the Church's treatment of Catholics who are gay, and how to approach couples who live together without being married.
Many campaigners and more liberal Catholics would like to see a change in Catholic doctrine on issues ranging from homosexuality to contraception - a topic also expected to be debated at the synod.
But observers say the meeting is not likely to change Catholic doctrine on the family but will focus instead on how the Church's teachings can be adapted to modern lifestyles.
Church attitudes towards same-sex couples is another controversial issue facing the synod.
The run-up to the summit was dominated by a row over a Catholic priest who was dismissed from his post at the Vatican after he publicly announced on Saturday that he was in a gay relationship.
A Vatican spokesman called Polish-born Krysztof Charasma's coming out a "very serious and irresponsible" move because it placed synod participants under "undue media pressure."
Charasma, who held a post in the Vatican's office in charge of guarding Roman Catholic doctrine, said in an interview with Italian daily Corriere della Sera that he was a homosexual and was living with another man.
"It's time the Church opened its eyes and realised that offering gay believers total abstinence from a life of love is inhuman," Charasma told the daily.
During a formal mass at St Peter's basilica on Sunday, Francis defended marriage as an unbreakable bond between man and woman and said the church should not be influenced by "passing fads or popular opinions."
But the pontiff also said that a "closed doors" church "betrays herself and her mission, and, instead of being a bridge, becomes a roadblock."
The issue of homosexuality was also highlighted during the Pope's trip to the US last month, where he had a private meeting with a gay former student of his and his boyfriend at the Vatican mission in Washington.
During his visit to Washington, Francis also met Kim Davis, a Kentucky local official who recently gained attention for refusing to issue marriage licences to same-sex couples.
After his election in 2013, Pope Francis reaffirmed the Catholic Church's position that homosexual acts were sinful, but said homosexual orientation was not.
"If a person is gay and seeks God and has good will, who am I to judge?" he said.
