Kepler, the father of modern physical astronomy, believed that the world is ordered by Archetypes . As quaint as this may seem, I argue that Kepler's archetypes provided methodological and epistemological solutions to problems in physical astronomy acknowledged during his time. ;Kepler used the assumption of a harmony between the archetypal and physical world to argue for the legitimacy of certain methodological innovations. The main difficulty facing astronomers at that time was the availability of observationally equivalent competing astronomical hypotheses. Kepler's (...) solution was to argue that the hypotheses could be distinguished between by proper testing and by bringing in considerations from other disciplines, especially physics. Kepler's account of the proper testing of hypotheses, though modern in appearance, was grounded in his archetypal cosmology. The use of physics in astronomy, also a modern innovation, was not considered to be methodologically sound during Kepler's time unless certain conditions were met. Under Kepler's archetypal cosmology these conditions were met, thereby legitimating the use of physics in astronomy. ;Kepler's archetypes play another role in his physical astronomy. The Aristotelian account of physics still dominant was qualitative in character. The use of mathematical physics was acceptable if it was grounded in qualitative theory, which Kepler was unable to fully provide. I argue that Kepler's archetypal cosmology enabled him to overcome this conceptual barrier. While Kepler agreed with Aristotle that mathematics is unable to reveal anything about physical causes, he believed that the archetypes are not limited in this manner. For Kepler, God's only reason for creating physical powers was to instantiate the archetypes; hence a study of archetypes can provide information about physical causes. When Kepler was unable to attach mathematical models to qualitative physical theory, he attached them to archetypal models, thereby legitimating their use in physics. ;Kepler's archetypes are no longer scientifically significant. At the time, however, they functioned to break down some of the conceptual barriers to his new physical astronomy. As a result, understanding Kepler's archetypes is of paramount importance for understanding his role in the scientific revolution of the sixteenth and seventeenth centuries. (shrink)