bers in a group decision situation is used in a prototype of a group decision support tool that explicitly computes and presents the differences between the individual positions held by each group member to help the group describe and define the parameters of the decision problem. A collaboration model based on two stages, one of group structuring (communication), and one of individual discrimina- tion (appropriation) is proposed. These stages alternate as each individual learns about other group members preferences, to ac- commodate other inputs and preferences, or to explore the problem. Information regarding the sources of disagreement between group members' positions and the changes that would be needed to achieve equal results are provided by the system, to help achieve a common solution (if possible).