Deliberative democracy is a normative ideal of democracy. This model is a proposal for the regeneration of the legitimacy of our institutions, but also a mechanism for decision making. It is based on two different dimensions: a procedural dimension where the model demands the inclusion and an equal capacity to influence the final decision of all those affected (Cohen, 1989; Bohman, 1996; Habermas, 1992 ...) and a substantive dimension where the political decisions are made through a collective procedure of argumentation and public discussion. If these conditions are recognized, the decisions will be more rational and better decisions. This paper has two aims. First I will present the key elements of this epistemic conception of political legitimacy. Second I will show the challenges it faces. On a one hand, the counterfactual of many of its postulates and on the other, the obvious problems of bias consensualist of this model.