How did Psychology of World Views prepare the way for Karl Jaspers’s later philosophy?

Psychologie der Weltanschauungen (“Psychology of World Views”), published in 1919, served as a foundational text that foreshadowed the core themes of Karl Jaspers’s later philosophical system.1

Although Jaspers originally intended the work to define the limits of psychological understanding regarding humanity, it effectively bridged the gap between his background in psychology and his transition into formal philosophy. The work prepared his later thought in several key ways:1

• Demarcation of Knowledge: It investigated the boundaries between science—which provides universally valid, apodictic knowledge of facts—and philosophy, which Jaspers came to view as a subjective interpretation of Being.1
• Focus on Existence: It introduced the concept of illuminating the totality of human existence, moving beyond mere "being-in-the-world" toward the realization of an individual's "freedom of being".1
• Methodological Development: By attempting to clarify the relationship between philosophy and science, the book helped Jaspers refine his goal of creating a philosophy that remained independent of science without attempting to replace religious belief.1

These germinal ideas were subsequently elaborated upon throughout the 1920s, culminating in his major systematic works published in the early 1930s.1