Mediaeval Christian polemicists treated useful falsehood as probable truth

Evidence

Theological standards did not supersede, but they helped to identify, the truth. Authors with didactic and moral intentions formed the belief that some ‘facts’ were true, because those ‘facts’ served the meritorious purpose of exposing error. Other authors whose intentions were a little less lofty, in histories and treatises composed to amuse and instruct, naturally took it that a more instructive and more amusing alternative was true, or at least was not certainly untrue; and the version that was more discreditable to Muhammad or to Islam was the more edifying, instructive and amusing; in fact, the more probably true. It would be anachronistic to say that such an attitude showed indifference to abstract truth; it was a question of finding the best means to recognise what was true. It seemed more reasonable to decide that what suited the author’s purpose was true, provided his purpose was a sufficiently laudable one, than to decide according to the abstract reliability of his sources of information. — Norman Daniel, Islam and the West, 1385

Categorization

• XREF: Connects to how any polemic or advocacy epistemology treats usefulness as a truth criterion — parallels colonial-era historiography and modern motivated reasoning. — connects to: The praised Christian ideal of self-denial is built on a falsehood; Some political falsehoods aim at affirmation of authority, not belief — Russell Muirhead and Nancy L. Rosenblum, A Lot of People Are Saying: The New…, 164
• DEEPTHINKING: The insight that truth-criteria were reversed — that a claim’s usefulness validated it rather than its reliability — is a dense, non-obvious epistemic point worth sitting with.