Medieval courts used ordeals of hot iron, boiling water, and cold water where evidence was lacking. The premise: God protects the innocent, so the water rejects the guilty and wounds heal clean on the righteous. The Church ended clerical participation in 1215, and the practice collapsed.
Economist Peter Leeson argues ordeals functioned rationally: guilty defendants, believing God would expose them, often confessed or settled rather than risk the ordeal, while the innocent, trusting divine protection, went through with it, and priests, knowing only believers would comply, could rig the water temperature. The system sorted guilt through belief itself.
The belief as it was lived: the ordeal was not a ritual but a technology, and it worked because God actually judged. Chroniclers record acquittals as miracles. Some modern scholars have argued, half seriously, that belief made it work: the innocent, trusting God, plunged willingly and healed faster.
If a system only works on believers, was it justice, theater, or applied psychology?