Medieval Christian polemicists knew Islamic Christology but falsely assumed Muslims accepted the Old Testament

Evidence

Oliver notes that al-Kâmil already believes in Jesus’ conception and virgin birth, his ascension into heaven, and his role as judge in the Final Judgment. Oliver seeks to convince him of the truth of the rest of Christian doctrine: the Trinity and the Incarnation, the divinity and death of Christ. You call us infidels, he says, because we worship the Trinity; you yourself unwittingly acknowledge it, he argues, when you recite David’s Psalm praising God’s name three times. Oliver has a fairly accurate knowledge of Islamic Christology, though he (like Alan of Lille) erroneously supposes that Muslims accept the text of the Old Testament, and that an argument based on the wording of a Psalm would carry weight with a Muslim opponent. — John V. Tolan, Saracens, 1034

Categorization

• XREF: Connects to the study of interfaith polemic and the failure of proof-texting across scriptural canons — echoes modern interfaith debates that assume shared text. — connects to: Some Christian thinkers knew arguments must rest on reason yet assumed Muslim premises; Medieval Christians weaponized accurate Islamic learning for polemics
• QUESTION: Worth chasing: did any Muslim scholar ever respond in writing to Oliver’s Old-Testament-based arguments, and how did that shape the crusade-era missionary literature?