 The next central question directly concerns gnoseology, for Kepler gives a psychological account of the path followed by sensible things into the mind. He resumes the scholastic species theory: immaterial species radiate from the sensible things and affect the sense organs by acting firstly on the “forecourts” and then on the internal functions (for the notion of ‘species’ in Kepler see Rabin 2005, which has found both favorable and critical reception in the literature). They arrive at the imagination and from there go over to the sensus communis, so that, according to the traditional teaching, the sensible information received is now able to be processed and used in statements. From here onwards, the sensible things are “preserved in the memory, brought forth by recollection, [and] distinguished by the higher faculty of the soul” (Caspar 1993, p. 269, cf. KGW 6, p. 214, lines 18–23; Engl. trans., p. 293). While harmony arises as an activity of the soul/mind consisting in relating quantitatively, Kepler adds, taking over the Aristotelian doctrine of categories, that harmony is a “qualitative relation” as well, involving the “quality of shape, being formed from the regular figures”, which provides the grounds for comparison (KGW 6, p. 216, lines 37–41; Engl. trans., p. 296). If this is how “things”, i.e., sensible entities, find their way into the soul in order to be compared, it by no means represents—as Kepler admitted—a sufficient explanation of how non-sensible things, i.e., mathematical entities, find their way into the mind. How do they come into the soul? Kepler accepted Aristotle’s criticism of Pythagorean philosophy concerning numbers: both Kepler and Aristotle are convinced that numbers constitute ontologically a lower class within mathematical entities (for Kepler, they are derived from geometrical entities). Nevertheless, Aristotle’s philosophy is insufficient to grasp the essence of mathematics. By aligning himself with Proclus, from whom he quotes a long passage of his Commentary on Euclides, Kepler defends Plato’s theory of anamnêsis against Aristotle’s doctrine of the tabula rasa. His discussion lies at the origin of the classical debate between empiricism and rationalism which was to dominate the philosophical scene for generations to come. A connection with idealism is, of course, apparent (see, for instance, Caspar 1993, Engl. trans., p. 269), and it is a fact that Kepler was positively received within German Idealism of the 19th century (Schwaetzer 2016, esp. 217–19). Historically, however, it seems to be more accurate to link his position with the philosophical tradition of St. Augustine.