Until now, Lange's criticism has touched Wolffian cosmology: Lange explicitly indicated that he would ignore ontology, because Daniel Strähler had earlier reviewed it thoroughly enough. Next in Lange's line of investigation is then psychology or the study of human soul. Lange's general line of attack is again to claim that Wolff tries to combine idealism and materialism with disastrous results. It takes no genius to guess that Lange is speaking of the topic of pre-established harmony between souls and bodies.
The idealistic feature of pre-established harmony lies in the complete independence of soul from body – bodies cannot affect soul in any manner. Lange points out some obvious incredulities in this notion: for instance, if nothing outside couldn't have affected me, I can't have learnt anything, but instead all my knowledge has mysteriously awakened within my soul.
The idealistic side of the pre-established harmony is only ridiculous in Lange's eyes, and it is the materialistic or deterministic side that Lange finds truly worrisome. Even though bodies cannot literally affect soul, the order of bodily events is mirrored in all details by the order of mental events. Now, because the bodily events occur in the deterministic material world, it appears that the changes in the soul must also be deterministic. True, soul would not be determined by external events, but it would still be internally determined by its own states.
Lange suggests that the determinism of soul is implicit already in Wolff's notion of the soul. Wolff thinks that the central element of soul is its force of representing external reality. Here Wolff clearly emphasizes the cognitive side of soul and especially mere passive cognition of the deterministic world outside human influence. What is then ignored is the volitional side of humans – there are no real choices, because human soul just follows automatically the course which has the weightiest motives. Human mind is just like a computer that has been programmed to strive for certain things, and given the situation, the mind will act in a way that will be beneficial for achieving those goals.
Similar faults Lange finds also in Wolff's notion of the infinite spirit or God, as we shall see next time.