Empirical research and theoretical treatments of conceptual change have paid little attention to the distinction between knowledge and belief. The distinction implies that conceptual change involves both knowledge acquisition and belief revision, and highlights the need to consider the reasons that beliefs are held. We argue that the effects of prior beliefs on conceptual learning depends upon whether a given belief is held for its coherence with a network of supporting knowledge, or held for the affective goals that it serves. We also contend that the nature of prior beliefs will determine the relationship between the knowledge acquisition and the belief revision stages of the conceptual change process. Preliminary data suggests that prior beliefs vary in whether they are held for knowledge or affect-based reasons, and that this variability may predict whether a change in knowledge will result in belief revision.