ABSTRACT
This chapter explains what experts are and what distinguishes them from a special kind of non-expert: Laypeople. It discusses structural features of experts' and laypeople's knowledge. The chapter addresses the common ground model of communication, as it has been suggested by Clark. It allows for modeling the impact of knowledge on mutual understanding. The chapter describes how problems in expert–laypeople communication might be characterized ascollateral damage of developing expertise. It illustrates three challenges confronting experts: Building common ground on technical concepts, being polite as well as clear, and establishing and maintaining trust. The quality of estimation is influenced by the expert's experience with laypeople and the type of professional vocabulary. The quality of these estimations then impacts their adaptation in discourse with laypeople. The needs related to the social balance between communication partners might counteract the cognitive need of laypeople to gain, for example, a clear, direct explanation.
