With others we distinguish different levels of communication involved in a negotiation process.  The most basic (which we call haggling) is an exchange of offers and requests of actions by the participants.  For example: "If you hold the door open, I will carry the box" or "Can anyone tell me where the nearest shop is, as we have run out of coffee". However in more formal negotiations such haggling actually takes up a very small amount of the time spent during negotiations.  It seems that a lot of time is spent discussing the participants goals and what the participants percieve as possible in the target domain.  Thus the next of the two levels we distinguish are the exchange of opinions of what the target domain is like, in particular how actions of the participants (and others) might change the state of the target domain, we call this viewpoint exchange.  For example: "If a flood plain was built, this would reduce the severity of any flooding", or "Even if we build higher dykes, this will not prevent all flooding".  The last level is the communication and reformulation of goals.  This is perhaps the most important but least understood aspect of negotiation, which we will call goal exchange.  In this paper I do not consider goal change or reformulation  but concentrate on what must be the case concerning the view points and goals for haggling to occur.

A simulation is shown where agents have different beliefs. The conditions when haggling occurs in this are explored. The differences often drive the dialogue. Signaling beliefs about possibilities can determine outcomes.