The only way of obtaining a comprehensible world-theory therefore is by construing the material universe after the analogy of the spiritual. In which case we construe both the elements (centers of force) and the primary substance as spiritual realities, the former representing an infinite variety of states of development, the latter as an infinite personality.
Lotze's psychology is likewise affected by his metaphysics. According to him the relation of soul and body is but a single example of interaction in general. Just as atoms can transmit impulses from one to another, so can the soul and an atom of the nervous system likewise transmit impulses from one to the other. Lotze sees no ground therefore in the principle of the conservation of energy for surrendering the common (Cartesian) conception of the interaction of soul and body. He makes a thorough study of the difficult problem of distinguishing between such mental phenomena as find their causes within the soul itself, and such as have their causes in the influences of the nervous system. Among the former are memory, reflection, the aesthetic and moral feelings, etc.; among the latter, sensations, which merely furnish the materials of thought.—Of Lotze's more specifically psychological theories we must first of all mention his ingenious doctrine of "local signs" (i.e. the specific sensations which furnish the basis of the construction of the theory of space), and then also his fine description and analysis of the relation of feeling and idea.
Although Lotze means to defend the common (Cartesian) theory of the interaction of soul and body, in his metaphysics, based on analogy, he has nevertheless made some important modifications. The interaction of soul and body is no longer (as in Descartes) an interaction of
