The aims of this paper are (A) to clarify what deliberative democracy is and how it is new compared to conventional democratic theories, and (B)  to explain the affinity between deliberative democracy and environmental politics. The arguments here unfold in three stages: first, in reflecting  back on the deliberative turn in democratic theory, I will characterize deliberative democracy as a process of "the transformation of preferences."
Deliberative democracy that has become an active research topic since the 1990s is new compared to conventional democratic theories in the  sense that it focuses on the function not so much of representing citizens' preferences as of transforming them. Secondly, I will explain why the  practice of deliberation leads to the transformation of preferences from the viewpoint of "the inclusion of the other" referring to Habermas'  discourse ethics. The practice of deliberation presses the deliberators to change their given preferences due to the "moralizing effect of public  discussion" by which they are urged to take account of the views of others to provide a public reason that can be accepted by them. Finally, I will  make clear an advantage of appealing to deliberative democracy when arguing about environmental politics in terms of the spatial, temporal, and  ontological transboundariness of global environmental problems. What I want to show in this section is that environmental problems today are not  solvable unless our own viewpoints are expanded spatially, temporally, and ontologically and that deliberative democracy that values the function of 
transforming preferences can give us a powerful tool for engaging in a more progressive environmental politics.