Advocatus Diaboli: Reconstructing the Lost Adversarial Function of the Promotor Fidei for Modern Document Governance

This paper reconstructs the adversarial evidentiary method of the Promotor Fidei, the Catholic Church's formal Devil's Advocate - and demonstrates its application to modern document governance. The Promotor Fidei was required to object to every piece of evidence, not a sample; to propose mundane explanations before extraordinary ones; to surface self-interested motives behind conduct framed as principled; and to see objections answered under a hard gate before any process could advance. In 1983, the formal adversarial mechanic was dismantled while the office survived in reduced form. No secular equivalent exists today in contracts, AI regulation, or corporate governance. The paper formalizes the method as the Advocatus Diaboli Protocol (ADP), a seven-check instrument for structural document review, and reports the results of two demonstrations: a self-test against the author's own prior published work, and an independent pass against the actual legal text of the EU AI Act's systemic-risk provisions (Articles 51–56), as amended by Regulation (EU) 2026/1744. The empirical finding is reported honestly: most of what the protocol catches, careful generic skepticism also catches. The protocol's demonstrated non-redundant contribution is concentrated in one check, the seven-part extraordinary-claim admissibility gate drawn from Lambertini's criteria, which surfaced a gap that plain skeptical review missed even when deliberately looking for it. The same test also exposed a gap in the protocol's own design: none of its seven checks question a document's selective disclosure of its own findings. The complete protocol is included as an addendum, self-contained and ready for use.