Conceptual change or multiple representations?

Several of the contributions to this issue take a common position in central questions. Conceptual change is discussed as a process, which leads from one coherent mental structure to another, which represents the world more adequately. Radical deep rooted transformations are hypothesized. In the commentary this view is compared with competing notions of knowledge completion and revision, the knowledge in pieces hypothesis, the multiple mental representations theory, etc. The necessity to develop formalized simulation models of the process of conceptual change is emphasized. Relevant work in the field of AI on belief revision is addressed.