This essay examines the cometary theory of Johannes Kepler and his claim that an “ethereal spirit” could lead a comet to appear at a providential place and time. In his account of the comet of 1607, Kepler suggested that a spirit served as a navigational principle that steered the comet on a particular course. I argue that this principle was an extension of Kepler’s celestial physics and part of his larger conception of causes at work in the heavens. I also (...) explore the critical response Kepler received from the theological faculty at the University of Leipzig, where he planned to publish his account. I explain why Kepler turned to natural philosophy to resolve the opposition of his religious authorities and how this was received as a foreign incursion on Sacred Scripture. In my final analysis, I discuss whether Kepler ultimately abandoned spiritual principles in his cometary theory and arrived at a system of celestial physics that was fully free of animistic ideas. (shrink)