Two American mechanisms for privatizing law enforcement — 695 AD qui tam and the 1970 citizen suit — converged on the same design from unrelated motives, a mirror image of the Chandler thesis

Two devices in US law let a private party sue to enforce public law, and they share a functional shape without sharing a lineage. Qui tam descends from a 695 AD Anglo-Saxon bounty decree and privatizes enforcement by making it profitable to report a violation. The 1970 Clean Air Act citizen suit was invented in living memory out of distrust of agencies — fear that industry would capture regulators — modeled on civil-rights litigation, and pays no bounty at all. Same output ("any citizen may sue to enforce the law"), opposite inputs: reward versus grievance, medieval versus modern, no documented transmission between them.

The pairing is valuable because it sits on the opposite side of the vault's central convergence debate from most of its cases. The standard multiple-discovery reading — reverse-mode differentiation reached separately across five fields — treats convergence as a real property of the object: any field reaching for gradients re-derives it. Chandler's transmissionist thesis is the rival: apparent independence is usually disguised shared descent. Qui tam and the citizen suit fit neither cleanly. They are not shared descent (no lineage links them), but they are also not one idea an object forces on every comer — they were built for unrelated reasons and merely coincide in structure. This is convergence-by-different-motive, the mirror image of Chandler: not "independent discovery is secretly repackaged prior work" but "independent invention can land on the same structure for completely unrelated reasons."

It joins the vault's other genuine cross-field convergences — observation-1981-convergence-testimony-wrong-in-detail-right-in-shape (testimony wrong in detail, right in shape) — as a case where the reason for convergence, not just its fact, is the finding.

The observation inherits the soft sourcing of its citizen-suit half and stays seedling until a primary is read — see question-verify-clean-air-act-citizen-suit-anti-capture-origin.