Both Christians and Muslims understood the other as a corruption of their own truth

Evidence

This is not an exhaustive list of examples, and it is hardly necessary to seek many. Islam was assimilated in practice to heresy, both by its measure of agreement with some classic heresies, and by the colloquial use of the word. Both these senses related it to Christian doctrine. Just as Muslims believed that the doctrines held by Christians were a corruption of those teachings of Islam which God had revealed to them through Jesus, so Christians could only see Islam as a corruption of Christian truth. — Norman Daniel, Islam and the West, 1039

Categorization

• XREF: Directly instantiates the vault’s Jew-Arab enemy genealogy — each monotheism reads the other as derivative corruption — a classic mechanism of producing the constitutive outside.
• DEFINE: Shows how the loose category ‘heresy’ functioned as the operative mechanism for assimilating a foreign religion to one’s own doctrinal frame.
• QUESTION: Worth chasing: does the symmetry described here (both sides calling the other ‘corruption’) disturb the asymmetry the modern vault claims — that only the West’s construction survives as hegemonic?