In a multi-agent environment, where selfmotivated (selfish) agents try to pursue their own goals, cooperation can not be taken for granted. Cooperation must be planned for and achieved through communication and negotiation. We look at argumentation as a mechanism for achieving cooperation and agreement. Using categories identified from human multiagent negotiation, we present a basis for an axiomatization for argument formulation and evaluation. We offer a logical model of the mental states of the agents based on a representation of their beliefs, desires, intentions and goals. We present argumentation as an iterative process emerging from exchanges among agents to persuade each other and bring about a change in intentions.