Ehrenfels himself assigns an important biographical role to his last major work in the philosophy of mathematics, while its actual philosophical and mathematical significance is much more modest, as we will see. Ehrenfels states in the preface to Das Primzahlengesetz that, after a long depression following WWI, the contemplation of the “field of numbers and their eternal, necessary connections” soothed his agonized spirit (“Weltangst”) (Ehrenfels 1922, III). In the preface to the work he retraces the development of the core idea of the book, describing very poetically how in April 1919 the idea “blossomed” in his mind about the distribution of prime numbers (Ehrenfels 1922, IV: “An einem warmen Aprilvormittag 1919 ist mir – in der Sonne gelagert neben der Gruft meines Vaters – „der Knopf aufgegangen” für das Wesentliche der Lösung.”) Ehrenfels himself at first took it only as a rediscovery of already well-established mathematical insights, but having been informed by his friend and colleague the mathematician Gerhard Kowalewski that the matter of the distribution of primes was far from settled, Ehrenfels tried to work out his idea in a more systematic fashion, convinced to have hit on something new and worthwhile.