Christians constituted Islam as a Christian heresy, not a foreign religion

Evidence

Reversing this Muslim attitude to themselves, Christians in their turn found a place for Islam as a deviation from the Church, that is, as a heresy. Heresy is in a familiar and identifiable relation to the whole truth which the Church represents; there is a’most a family of Christian error in which Islam may be found a place. The great proportion of Christian truth contained in Islamic belief made this possible, although, as a heresy, Islam would always remain peculiarly formidable and, in fact, unique. — Norman Daniel, Islam and the West, 1020

Categorization

• XREF: Closely matches the vault’s existing claim that ‘Islam’ is constructed as the West’s constitutive internal outside — placing Islam as heresy (internal deviation) rather than alien religion frames it as a Christian self-problem, echoing how Anidjar/Aziz show Islam functioning as the West’s constitutive other.
• DEEPTHINKING: The mechanism — that Islam’s high proportion of shared Christian truth made it MORE formidable as heresy than as pure alien religion — is theologically generative and non-obvious; same-family error is threatening precisely because it is near-identical.