Good article from the late Father Harden.
Father Hardon was wonderful. When I asked him for advice, he was blunt, compassionate, and so very wise. A great man and priest.
It is always useful to define the term. If a had a quarter for each time the distinction between the schism, which we technically have with the Orthodox (although it is discouraged to use such harsh a term), and heresy, of which we accuse the Reformers, is muddled up, I'd be a rich man.
This looks like a good one!