De Haro and Elizalde (2026) argue Einstein's 1907–1916 route to geometric GR needed two separate heuristics because he read the invariant ds as a Gaussian geometric 'line element' rather than operationally as proper time

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As a historiographical companion to their operational reconstruction (claim-de-haro-elizalde-2026-reconstruct-linearized-gr-from-conatus-and-potentia), de Haro and Elizalde argue that Einstein's historical path to the geometric formulation of general relativity was "convoluted" for a specific conceptual reason. On their account, Einstein's 1912 use of the elevator Equivalence Principle fixed only the temporal component g₀₀ of ds² — predicting, they say, just half the observed light deflection — so he then needed a second, separate heuristic, the rotating-disk / Ehrenfest-paradox argument, to motivate the spatial sector. The paper names the cause: "Why did Einstein feel compelled to proceed in this convoluted manner? … Throughout this crucial period, unlike Minkowski, Einstein did not make the operational interpretation of ds as the differential of proper time the central organizing principle of his construction. Instead, heavily influenced by Marcel Grossmann and the legacy of 19th-century mathematics, he viewed ds through the lens of Gaussian surface geometry." The two heuristics — "using the elevator to motivate the temporal sector and the rotating disc to motivate the spatial sector" — "eventually led Einstein toward a fully geometric formulation of gravitation," whereas (the authors argue) starting from Minkowski's 1908 operational reading of ds as elapsed clock time collapses the two steps into one.

This is interpretive and load-bearing for the paper's narrative, not a settled textbook fact: it records what de Haro and Elizalde argue about Einstein's conceptual development, not independently confirmed history of his reasoning. The claim connects to the vault's history-of-GR material — the renaissance of general relativity and the philosophy-of-physics cluster around Lehmkuhl and Curiel — and would need a dedicated Einstein-historiography source to carry weight beyond this paper's framing. A specific internal tension is noted in the frontmatter watch_flag: the paper's own spatial-sector argument is contested by a source it cites (Tartaglia 1999).