In this paper, we propose a flexible dialogue mechanism through which a set of agents can establish a coherent set of public beliefs. Flexibility and coherence are achieved by decomposing the dialogue mechanism into two parts, a backbone protocol and a set of conversation policies. The backbone protocol maintains the set of arguments put forward by the agents, and each agent uses a preagreed argumentation theory to extract the set of public beliefs from the context. The flexibility is achieved by distributing the other functions of the dialogue mechanism among a set of conversation policies, some of which are public and some of which are private to each agent.