Russell reflected in 1914 on realizing the dream of empiricist epistemol-ogists: the explicit construction of the external world, or a reasonable facsimile, from sense impressions, hence from simple ideas. He adumbrated it in Our Knowledge of the External World, and a dozen years later Rudolf Carnap was undertaking to carry it out. Carnap’s effort found expression in Der Logische Aufbau der Welt. (Quine 1995, p. 10).