An examination of introspective evidence of artists and scientists on their creative processes suggests that the transformation of material in thought is the key problem for understanding creativity. A similar problem underlies the transformational process of understanding a metaphor. Evidence for transformations in thought under the impact of experiential anomalies is provided by examples from scientific thought and from dreams. Such transformations are guided by or express affective states or attitudes. Evidence for the productive role of affect in thought is presented from several sources, including research on the frontal regions of the brain and on the affective correlates of response to metaphor. It is suggested that an adequate theory of creativity must await further research on the anticipatory properties of affect and that a useful place to begin such research is with the response to metaphor. (David Miall)