 Many of Kepler’s thoughts about epistemology can be found in his Defense of Tycho against Ursus or Contra Ursum (=CU), a work which emerged from a polemical framework, the plagiarism conflict between Nicolaus Raimarus Ursus (1551–1600) and Tycho Brahe: causality and physicalization of astronomical theories, the concept and status of astronomical hypotheses, the polemic “realism-instrumentalism”, his criticism of skepticism in general, the epistemological role of history, etc. It is one of the most significant works ever written on this subject and is sometimes compared with Bacon’s Novum organum and Descartes’ Discourse on Method (Jardine 1988, p. 5; for an excellent new edition and complete study of this work see Jardine / Segonds 2008).