Usury

When: About the 16th century

Original rule: “Lend freely, hoping nothing thereby,” the Bible teaches. Interpreted literally, this prohibition against profiting on loans played a major role in the creation of the European credit markets during the Middle Ages. Bankers had to devise methods of profiting from moneylending without directly charging interest.

How it changed: The rule simply faded away as European capitalism developed during the Renaissance. The charging of interest forms the basis of the modern financial system, so economic history might have turned out quite differently had the rule stayed in place. The Islamic banking system, where usury is still prohibited, gives a pretty good picture of how finance might have worked without interest.

Slavery

When: The mid- to late-19th century

Original rule: No less an authority than St. Augustine said that Jesus Christ “did not make men free from being slaves.” As late at 1860, the church taught that it was not a sin to own another human being so long as the slave was treated humanely.

How it changed: The church never really took a firm stance against slavery until the practice was already largely banished in the Western world. Pope Gregory XVI was the first to criticize slavery in 1839, though he left a good deal of room for interpretation. It wasn’t until Leo XIII, the first 20th-century pope, that the church took a firm stance against slavery as a moral outrage. Today, the Catholic Church is at the forefront of efforts to eliminate modern slavery.

Vatican II

When: 1962-1965

Original rule: Traditionally, Catholic Mass was celebrated in the original Latin, with priests facing away from congregants. More generally, the institutions of the church maintained a level of distance from both followers and the modern world as a whole.

How it changed: Few events in church history have done more to change the way Catholicism is lived by its followers than the Second Vatican Council. In addition to allowing Mass to be celebrated in local languages, the church undertook a number of initiatives including the promotion of lay ministries, greater dialogue with other faiths, and more decentralization of authority to dioceses.

Capital Punishment

When: 1995

Original rule: The church was not traditionally opposed to the death penalty for particularly egregious crimes. Catholic theologians, including Thomas Aquinas, wrote vigorous defenses of its use. Some popes even issued death sentences themselves in their capacity as civil rulers.

How it changed: Support for the death penalty had waned in the church over the years, but it wasn’t until John Paul II’s 1995 encyclical that the Vatican’s opposition was stated explicitly. He wrote that although the death penalty was permissible in extreme cases when society was at risk, improvements in the modern judicial system made such cases practically nonexistent. Benedict XVI, the current pontiff, is a vocal critic of the death penalty and even publicly opposed its use on Saddam Hussein.

Limbo

When: 2007

Original rule: In traditional Catholic theology, limbo is the halfway point between heaven and hell where the unbaptized, including infants, go after death. Even though they had committed no sins, such people had not been cleansed of the “original sin” through baptism.

How it changed: Limbo was never a particularly popular concept with parishioners, and modern priests rarely discussed it. In 2004, John Paul II formed a commission to come up with “a more coherent and enlightened way” of describing what happens to infants who die. In 2007, Benedict signed a report recommending the concept be dropped. Instead of going to limbo, unbaptized babies would enjoy eternal happiness after death, but would not achieve communion with God.