Heresy began as the Greek word for making a choice
Today heresy sounds like a crime against faith. The Greek root, haíresis, simply meant a choice, then the school of thought a person chose, even the process of a young person weighing philosophies to decide how to live. How a word for choosing became grounds for execution is a story of church and empire merging.
A heresy is a belief sharply at odds with the accepted teaching of a religious body. It differs from apostasy, which means abandoning a faith outright, and from blasphemy, an irreverent word or act about the sacred. The term gained its hostile edge in the second century, when Irenaeus wrote Against Heresies to discredit the Gnostics, labelling his own community's teaching orthodox, from Greek words for straight belief. Early Christian writers also called a sound doctrine healthy and treated divisive teachers as sources of infection.
Power turned the label into law. Constantine the Great, who with Licinius had granted Christianity toleration, called the first ecumenical council to settle the dispute stirred up by Arius and then enforced its verdict with imperial authority. In 380 the Edict of Thessalonica under Theodosius I made Christianity the state religion, and with it heresy became a legal category. Within six years a Spanish bishop, Priscillian, was executed by secular officials, and prominent churchmen including Ambrose of Milan and Pope Siricius condemned his accusers. Yet in the roughly 700 years after Rome fell, according to historian David Collins, only one execution of heretics is known.
The picture changed in the eleventh and twelfth centuries, when organised movements such as the Waldensians and Cathars spread through northern Italy, southern France and Flanders. The church answered with the Cathar Crusade and later the Inquisition, whose Latin title meant an inquiry into heretical depravity. Its most famous defendant, Galileo, was found vehemently suspect of heresy for teaching that Earth moves around the Sun, recanted, and spent the rest of his life under house arrest; most historians treat his case as an exception in the relationship between science and Christianity.
Protestants prosecuted heresy too. Michael Servetus was condemned by both Reformed and Catholic authorities for rejecting the Trinity, and under Mary I around 290 people were burned in England between 1555 and 1558. England's last execution for heresy came in 1612, and the Catholic Church's last, of a Spanish schoolmaster named Cayetano Ripoll, in 1826. Modern Catholic doctrine officials tend to criticise writings for ambiguities and errors without using the word at all.
Source: Heresy
