In an interview about his recent book, Know the Heretics, professor and priest Justin Holcomb lays out a definition for the term:
A heretic is someone who has compromised an essential doctrine and lost sight of who God really is, usually by oversimplification. Literally, heresy means “choice”—that is, a choice to deviate from traditional teaching in favor of one’s own insights.
For Christianity, the Nicene Creed is a historic, globally accepted creed that encapsulates the Christian faith in a short and rich summary. If someone holds to the Nicene Creed, we should not call them a heretic. Not even if we believe they are in error on the details or on other doctrines. I think a good shorthand for heresy, is to ask, “Can they say the Nicene Creed and mean it without their fingers crossed?”
His take on the heresies most prevalent today:
I think many of the old heresies are repackaged today. For example, there is plenty Sabellian Modalism—the belief that God is one actor wearing three hats—floating around today. Also, I think a repackaged version of Pelagianism is most “live” today. (My summary of Pelagius’ heresy is “God has already given us the tools we need.”)
Pelagius correctly saw human nature as something good created by God, and there is no such thing as original sin. Adam’s sin in no way makes humans guilty or corrupt. Humans by nature have a clean slate — a state of neutrality — according to Pelagius. Potentially, then, one could live a sinless life and merit heaven, for there is nothing intrinsically sinful about humans. To me, this sounds like lots of the gobbledygook that is passed around today in popular Christian TV, radio, and publishing.
The Dish 