Langlois & Seignobos (1898) name diplomatics as the body of doctrine for authenticating charters, classing it among the auxiliary sciences feeding External Criticism

diplomaticshistorical-methodexternal-criticismmabillonlanglois-seignobosauxiliary-sciencessource-evaluation

In the "Auxiliary Sciences" chapter (pp. 49–50) of their Introduction to the Study of History — the founding methods manual of professionalized academic history — Charles-Victor Langlois and Charles Seignobos define the discipline Mabillon founded by name and by function. Verifying a document's genuineness, they write, requires "reasoning power and knowledge": a trained logician cannot tell a genuine charter from a spurious one without first learning, by comparing many securely genuine specimens, the features that distinguish the authentic from the forged. "This body of doctrines, observations, and results, calculated to assist the criticism of diplomas and charters, does exist; it is called Diplomatic."

This is a description of diplomatics as Mabillon founded it in 1681 — comparison of a document's own hard-to-fake features against dated exemplars to settle whether it is what it claims to be. The 1898 text groups Diplomatic with Palaeography, Epigraphy, and Philology as auxiliary sciences, all feeding the first of its two evaluative operations: External Criticism, which judges a document's authenticity, as distinct from Internal Criticism, which judges whether its content is believable.

This supplies the verbatim primary passage behind the vault's existing finding that diplomatics occupies the authenticity axis alone. That note reached the placement by structural inference from External Criticism's stated territory ("the writing, the language, the form, the source") and recorded that a directly-quoted version naming Diplomatic was not yet promoted; this is that quote. It locates the whole Gates/Mabillon diplomatics cluster on one of the two axes that the Admiralty Code and reliability-aware RAG later hold as a coupled pair.