Technologies that electronically mediate conversation, such as text-based chat or desktop video conferencing, draw on theories of human human interaction to make predictions about the effects of design decisions. This lecture reviews the theory that has been most influential in this area: Clark's theory of language use. The key concept in Clark's theory is that of common ground. Language is viewed as a collaborative activity that uses existing common ground to develop further common ground and, hence, to communicate efficiently. The theory (a) defines different kinds of common ground, (b)...