Husserl originally assumed that logic should expect the clarification of its own foundations from psychology. However, questions and doubts about how the undeniable objectivity and strict universality of logical truths can be understood psychologically led him out of the sphere of such foundational attempts: In his "Prolegomena to Pure Logic," the first volume of the "Logical Investigations," Husserl presented a critical assessment of logical psychologism in 1900, the results of which remain undisputed to this day. In the six detailed studies of the second volume (1901), the broadly outlined program of the "Logical Investigations" receives its first positive treatment. They also provide the fundamental lines of Husserl's phenomenological method, which will always be associated with his name.