Although the name and nature of these roles varies from group to group, the most common are the facilitator, a timekeeper, an empath and a secretary or notes taker. Not all decision-making bodies use all of these roles, although the facilitator position is almost always filled, and some groups use supplementary roles, such as a Devil's advocate or greeter. Some decision-making bodies opt to rotate these roles through the group members in order to build the experience and skills of the participants, and prevent any perceived concentration of power.[25]