“What is a heresy, and what is the historical importance of such a thing?
“Like most modern words, “Heresy” is used both vaguely and diversely. It is used vaguely because the modern mind is as averse to precision in ideas as it is enamored of precision in measurement. It is used diversely because, according to the man who uses it, it may represent any one of fifty things.
“Today, with most people (of those who use the English language), the word “Heresy” connotes bygone and forgotten quarrels, an old prejudice against rational examination. Heresy is therefore thought to be of no contemporary interest. Interest in it is dead, because it deals with matter no one now takes seriously. It is understood that a man may interest himself in a heresy from archaeological curiosity, but if he affirm that it has been of great effect on history and still is, today, of living contemporary moment, he will be hardly understood. Yet the subject of heresy in general is of the highest importance to the individual and to society. We must begin by a definition, although definition involves a mental effort and therefore repels.
“Heresy is the dislocation of some complete and self-supporting scheme by the introduction of a novel denial of some essential part therein.” -Hilaire Belloc, The Great Heresies
The Great Heresies, by Hilaire Belloc