In the course of outlining his vision of a phenomenological psychology Husserl also discusses ontology and the method of free variation. The discussion of ontology, relevant because Husserl is considering relations between mental and physical phenomena, is second only to the discussion in Ideas II. The discussion of free variation, relevant because Husserl sees essences as central to the development of a phenomenological psychology, is more comprehensive than any other in the corpus, and in fact the relevant passages in Expereince and Judgement are edited versions of this discussion.

The Phenomenological Psychology was compiled from several lecture courses given between 1925 and 1928 at Freiburg. This is arguably the most detailed treatment Husserl gives of the relationship between phenomenology and empirical psychology. While Husserl acknowledges that psycic phenomena depend on physical (ie.e. neural) phenomena, he is an ardent critic of psycho-physical psychology as it was practiced in his day.