Although we are principally interested in highly symmetrical collaborative systems, the degree of symmetry is in fact a continuous variable: Designers have to decide whether they provide to artificial and human agents a more or less equivalent a range of interface actions and interaction possibilities (i.e. both in action mode and discussion mode - dimension 1). The particular choice along this continuous axis may also vary along dimension 2 (what is negotiable). It also depends on the rights and obligations inherent in agents' social-institutional status, even when transferred to the human-machine case. For example, in a 'traditional' teacher-student interaction, the teacher may conventionally have the right to make the dialogue move "NEGATIVE-EVALUATION", with respect to a previous move of the student, whereas the student may not have the social right to make such a move. In practice, however, the degree of symmetry is also influenced by technical constraints. For instance, although in certain cases both 'teacher' and 'student' should have the social right to make an EXPLANATION move, often this is excluded for the student simply because the system will lack sufficient natural language understanding competence.
