We consider a simple model of interacting agents asked to choose between 'yes' and 'no' to some given question. The agents are described in terms of spin variables, and they interact according to a mean field Heisenberg model. We discuss under which conditions the agents can come out with a common choice. This is made using, in a social context, the notion of KMS states and phase transitions. This article is part of the theme issue 'Thermodynamics 2.0: Bridging the natural and social sciences (Part 2)'.
Keywords: KMS states; decision making; phase transitions; social laser.