Medieval Christian polemic began treating Judaism and Islam as parallel irrational faiths

Evidence

This linkage of anti-Jewish and anti-Muslim argumentation and this insistence on the irrationality of both rival faiths represents a crucial turning point in the portrayal of both Islam and Judaism in medieval Europe. — John V. Tolan, Saracens, 833

Categorization

• SEED: Article angle: how the ‘rational vs irrational religion’ binary was first assembled in the 12th century as a twinned argument against Jews and Muslims, and how that framing persists in modern atheist polemic.
• XREF: connects to: By 1250 the unity-of-God doctrine was common Christian knowledge about Islam; Medieval polemicists placed Islam midway between Jewish and pagan error; Protestant-Catholic-Islamic parallels in polemic relied on incredibly thin points