Arguments commonly used in discussions about design, planning, policy-making issues have not been adequately analyzed in the literature. The structure of such ‘planning arguments’ is discussed. Based on the conceptual framework of the ‘argumentative model of planning’ proposed by H. Rittel, an approach for their systematic and transparent evaluation by discourse participants is presented. Procedural implications for its application in the planning process are discussed, and the potential for information technology support for such processes explored.