What sort of democracies should open agent societies be? We present three normative models of democracy from political philosophy and consider their relevance for the engineering of open multi-agent systems: democracy as wise rule by an elite; democracy as the exercise of rational consumer choices by voters; and democracy as deliberative decision-making by citizens. We consider the implications of these different models for the design of open systems, in terms of the communications language, the interaction protocol, and the conflictresolution mechanism used by the agents involved. We also consider the issue of verifiability of the internal semantics of communications languages, and argue that a model of agent democracy based on deliberative democracy provides the basis for a form of verifiability which is stronger than a social semantics.