The work of Johannes Kepler offers clear examples of conceptual change. In this paper, using Kepler's work as a case study, we will argue that analogical reasoning facilitates change in knowledge in four ways: highlighting, projection, re-representation, and restructuring. We present these four mechanisms within the context of Structure-mapping theory and its computational implementation, the Structure-mapping Engine. We exemplify these mechanisms using the extended analogies Kepler used in developing a causal theory of planetary motion.