A formal two-phase model of democratic policy deliberation is presented, in which in the first phase sufficient and necessary criteria for proposals to be accepted are determined (the ‘admissible’ criteria') and in the second phase proposals are made and evaluated in light of the admissible criteria resulting from the first phase. Argument schemes for both phases are defined and formalised in a logical framework for structured argumentation. The process of deliberation is abstracted from and it is assumed that both deliberation phases result in a set of arguments and attack and defeat relations between them. Then preferred semantics is used to evaluate the acceptability status of criteria and proposals.