Ever since its first publication in 1883, Hermann Cohen's text The Principle of the Infinitesimal Method and Its History: A Chapter on the Foundations of the Critique of Knowledge has formed a puzzle for all but close followers of the Marburg school. The text is widely considered to mark a shift in Cohen's thought and to establish the most influential direction of the school, and with it began the school's enormous influence in German philosophical, legal and scientific thought in the three decades before the First World War. Intended, however improbably, to form something of a “popularization” of Cohen's ideas, the text formed the germ of Cohen's own philosophy as initiated in the second edition of his Kant's Theory of Experience two years later and developed in his late System of Philosophy (1902–1912). It is true that the puzzle for many readers of Infinitesimal Method was simply its contents, for despite its purportedly approachable form, it was widely considered extremely difficult and occasionally accused of being needlessly opaque. The philosopher Friedrich Kuntze noted that “Cohen's book is generally considered to be one of the most difficult books of German philosophy, and one can hear from considerate people that the only thing they understood in the work were the citations from foreign authors.” Kuntze claimed that this difficulty stemmed from the challenging conceptual nature of the infinitesimal as much as it did from Cohen's style.