Catholicism is one of the three major branches of Christianity, along with Protestantism and Orthodox Christianity. The Catholic Church is the largest denomination in Christianity. Its head is the Pope. The church has a long history and its position has evolved on many issues over the centuries.
Christianity grew out the churches established by missionaries, such as Paul, in the countries surrounding the Mediterranean Sea. During this time, much of the Mediterranean region was under Roman control. The Roman empire split into a Western and Byzantine empires in 395 CE. This political separation allowed Christianity to develop along separate lines, with different traditions and liturgy. The Western empire collapsed in 476 CE although the papacy continued in Rome. The relationship between the western Latin and eastern Greek churches gradually declined, particularly when the Franks gained sufficient influence with the papacy to cause their king to be crowned Holy Roman Emperor in 800 CE. This action was taken as a snub to the Eastern emperor and the Byzantine empire. Political and theological differences finally resulted in the East–West Schism which separated the empires and churches in 1054 CE. The Western church, lead by the Pope in Rome, became the Catholic Church, generally located in western Europe. The Eastern church became known as the Orthodox Church and was generally located in the Eastern Mediterranean.
The official sacred text is the Latin Vulgate translation of the Bible. The church maintains lists of approved translations, which usually differ from Protestant versions. Throughout the Middle Ages, the Bible was only available in the Latin Vulgate translation in the Western church.  However, most lay Christians were illiterate or could not read Latin. In 1199, the Catholic Church banned any further unauthorised translations of the Bible.
- "[...] the Catholic Church resisted the idea of bible translations, not only into modern languages currently, but even when the Latin Vulgate was written about 1000 years earlier. Catholics wanted their interpretation to be the only interpretation. It wasn't a conspiracy, just a firm belief that their interpretation was the right one. "
The papacy has been based in the Vatican during the early church and on a continual basis since 1378. The Vatican is now a small independent state within Rome. For this reason, the senior leadership of the Catholic Church is sometimes referred to as "the Vatican" or simply "Rome".
In 1517, Martin Luther sent his Ninety-Five Theses to several bishops. In it, he criticised Catholic theology and practices, including the sale of indulgences. He also emphasised personal Bible reading and translations into local languages. This eventually caused a schism in the church and lead to the protestant movement.
The English king Henry VIII was involved in a divorce dispute with the Catholic Church. In 1534, the king declared himself the head of the Church of England, causing a schism with Rome and the king to be excommunicated. The Church of England was later reunited with the Catholic Church in 1555. The Church of England again schismed in 1558 under Elizabeth I.
Since 2013, Pope Francis was selected lead the church.
The contemporary Catholic Church is characterised by:
- Opposition to contraception
- Opposition to abortion
- Opposition to homosexual acts and homosexual marriage
- Opposition to fornication and adultery
- Remarriage after divorce is forbidden
- Freedom of conscience
- Freedom of religion: people are not forced to believe or stay within Catholicism.
Many of these policies are also used by some other denominations. Although contraception is officially banned by the church, this teaching is largely ignored in many cultures.
In a break with the inaction of previous leaders, Francis has spoken on a range of social and environmental issues. Francis criticised the senior leaders of the Catholic church as being narcissistic, hardened, excessively active, uncoordinated, non-spiritual, boastful bureaucrats. 
Dogma and practices
While most Christian apologetics are common to Catholicism, there are some doctrines, practices and related apologetics that are strongly emphasised or uniquely Catholic:
- Apostolic succession
- Transubstantiation and Eucharistic miracles
- Veneration of Mary and Marian apparitions
- Opposition to women priests
- Celibacy of priests
- Papal infallibility (which only applies in some circumstances)
- Usually a non-literal interpretation of the Bible
- Catholics believers do not have such an emphasis on interpreting the Bible for themselves. This was probably motivated by the desire to exercise control on how the Bible was interpreted.
- The Bible is not the final authority (referred to as Sola scriptura). The church emphasises the role of apostolic tradition or oral teaching, as well as the Bible. 
- Hinted at potential salvation for non-believers: "those who, without fault, have not yet arrived at an express recognition of God" . Apostates are probably out of luck.
- A sin is either "moral" or "venal". 
- Venal sins have a finite "temporal punishment" inflicted before death or in Purgatory 
- Temporal punishments can be remitted by indulgences.
More Catholic doctrine
The Crusades were a series of military expeditions sent by various European kingdoms during the Middle Ages. They were directly initiated or sanctioned by the Catholic Church. They aimed to recapture Jerusalem from Islamic states, persecute heretics and Jews, and gain converts by force.
Initiated in 1250s, the Inquisition refers to various institutions in the Catholic church to promote orthodoxy and persecute heretics, potential apostates and Jews. During the Late Middle Ages and early Renaissance, these institutions were active in many questionable activities including torture to gain forced confessions (although less than other tribunals of the time), execution of thousands of people by burning people alive, confiscation of property, forced exile, imprisonment, anonymous denunciation and censorship. The last execution by the Inquisition was in 1826.
Historic opposition to science
Historically, the church has opposed scientific discoveries that were considered threatening to its theology. In 1633, the Inquisition tried and condemned Galileo Galilei over his astronomical observations that supported the heliocentric theory.
In recent times, the church has become more accepting of science. It reversed its position regarding Galileo in 1992 and has since praised Galileo's discoveries. The current view of the church is that science and faith cannot be in conflict:
- "methodical research in all branches of knowledge, provided it is carried out in a truly scientific manner and does not override moral laws, can never conflict with the faith, because the things of the world and the things of faith derive from the same God "
The Catholic Church generally (and unofficially) accepts both evolution and creationism but rejects young Earth creationism. Some Catholic organisations argue against evolution. Incidentally, Gregor Mendel was a Catholic friar and the founder of genetics.
Historic sale of indulgences
Indulgences are a remission of temporal punishment for venal sins that have already been confessed. They are granted by the clergy for various works, such building churches visiting shrines, charity or pious conduct. The specific actions that qualify have been revised from time to time. During the Middle Ages, indulgences were available for monetary payment and became extremely popular. They were used to fund large building projects, such as cathedrals, hospitals, schools and to pay for costly appointments. Many indulgences were sold that were contrary to official church doctrine; accusations were made against Johann Tetzel that he told an indulgence for full forgiveness for all future sins. The sale of indulgences were a means of defrauding credulous believers and gaining immense wealth for the church. Apologists argue that the sale of indulgences was never official church policy.  However, Pope Leo X himself gave indulgences for payment. In the contemporary church, payments are no longer an acceptable means of gaining indulgences.
Although technically banned, the buying and selling of religious offices became widespread in the 9th and 10th centuries. This is referred to as simony. The practice reduced after reforms were introduced. These positions were often funded by the sale of indulgences or relics.
Christians have persecuted Jews since the early church. Many of first writers within the early Christian organisations that became the Catholic church were explicitly anti-Semitic (e.g. St. Augustine). It took until 1965 for the Catholic church to declare that contemporary Jews were not to he held responsible for the death of Jesus. 
Child sex abuse
Since around 2000, the world media has been reporting on widespread child sexual abuse committed by priests. The abuse mostly occurred between 1950 and 1980. At the time of abuse, the age of the victims was typically between 11 and 14  but was as low as 3 years old. The Catholic church, being the largest denomination in Christianity, is the church of a significant proportion of abusers. The Catholic church's response to abusive priests was often to cover up the abuse, using a "code of silence" and transferring the priests into new areas where they sometimes continued to abuse children. Information concerning criminal acts was not passed to the police. The U.N. Committee on the Rights of the Child said: 
- "[The Vatican] has not acknowledged the extent of the crimes committed, has not taken the necessary measures to address cases of child sexual abuse and to protect children, and has adopted policies and practices which have led to the continuation of the abuse by, and the impunity of, the perpetrators"
Current attitude to atheists and apostasy
The Catholic Church regards secularism as a threat:
"it is imperative that the entire Catholic community in the United States come to realize the grave threats to the Church’s public moral witness presented by a radical secularism which finds increasing expression in the political and cultural spheres."
- — Benedict XVI 
Some Catholic leaders claim that atheists are not fully human. 
- "Man is by nature and vocation a religious being. Coming from God, going toward God, man lives a fully human life only if he freely lives by his bond with God. "
"There is something not totally human if you leave out transcendent [God] and you [atheists] are not fully human. They have an impoverished understanding to what it is to be human. We are all made by God."
- — Cardinal Cormac Murphy O’Connor 
Leaving the church
Since the church does not impose any material punishment for leaving the church, the main adverse consequence is the potential disapproval from family and society. The penalty of apostasy in the Catholic Church is automatic excommunication.  Excommunication is said to be Latae sententiae because the sentence is automatically imposed, if the apostasy is a wilful act carried out by an informed person.  An excommunicated person is forbidden to receive the sacraments (communion, weddings, etc) but is still allowed to attend church events. 
Between 2006 and 2009, act of actus formalis defectionis ab Ecclesia catholica was a way to inform the church of defection. It is unclear if this is required for an apostasy to be considered "formal", rather than "material". This act required notification of a competent ecclesiastical authority.  After 2009, changes to canon law abolished this procedure and inquiries to find an replacement have not been answered. 
- ↑ 
- ↑ Darren Roberts, Where Did We Get A Bible?, 2012
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- ↑ 6.0 6.1 
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- ↑ A Report on the Crisis in the Catholic Church in the United States (John Jay Report), 2004
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- ↑ Address Of His Holiness Benedict XVI To The Bishops Of The United States Of America On Their "AD Limina" Visit, Thursday, 19 January 2012
- ↑ 13.0 13.1 
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- ↑ Code of Canon Law, Book 4, Part 2, Title 1, 1364 
- ↑ 16.0 16.1 Colin B. Donovan, "Heresy, Schism and Apostasy" 
- ↑ Actus Formalis Defectionis Ab Ecclesia Catholica, 13 March 2006
- ↑ Church Continues to Block Formal Cessation of Membership, 20/07/2011