The first volume of the Logische Untersuchungen, published in 1900, had approached the problems of logic from a strictly objective point of view. The colossal project of a Mannigfaltigkeitslehre in which all forms of possible theories would be deduced in a systematic manner, returned to the old dream of a Mathesis Universalis. The mathematical education of the author,¹ who once had been an assistant to Weierstrass, seemed to destine him to a brilliant career as a logician. The publication of the second volume, in 1901, was a surprise. The problem of the theory of knowledge, discreetly announced in the first volume,² was developed by a return to subjectivity.