Early Christian writers framed Islam as one more heresy, not a new religion

Evidence

Near the end of his life, in 743, as a monk of Mar Sabbas, John completed his Fount of Knowledge, a vast theological compendium consisting of three parts: the first on philosophical ideas, the second on heresies, and the third on the orthodox faith. Part 2, On the heresies, in some manuscripts is an independent text: it describes one hundred heresies in as many chapters. Of these, the first ninety-seven are largely derivative, copied with little change from earlier compendia; only the last three chapters, on iconoclasm, the Aposchites, and Islam, seem to be the original work of John of Damascus. The place of his description of Islam should be kept in mind: Islam is the last of one hundred heresies that have plagued the church. John will deploy against Islam the Trinitarian arguments habitually leveled against Jacobites and Nestorians, arguments for free will deployed against the Manicheans, and arguments in defense of crucifixes and icons from the iconoclastic dispute. From John’s perspective, Islam is not a new religion but the last in a long line of deviant Christianities. — John V. Tolan, Saracens, 343

Categorization

• DEFINE: Explains the conceptual lens: Islam was categorized as a heresy (deviant Christianity), the 100th in a list, not as a separate religion — which shaped how its tenets were attacked.
• XREF: Connects to the broader theme in Tolan’s Saracens about medieval Christian framing of Islam, and to how doctrinal box-fitting determines which arguments get deployed.