The aim of this article is to lay down the foundations of a critical sociology of democracy and participation. Based on Amartya Sen's capability approach, we identify four major pitfalls of classical theories on justice and deliberative democracy: 1) an excessive emphasis on the procedural dimension of democracy at the expense of its substantial value; 2) an ideal of deliberation that does not sufficiently account for the inequalities that characterize actual participative practices; 3) an ideal approach to rationality which is inconsistent with the plurality of reasons to value and arguments that can be observed in social reality; and 4) a focus on official or institutionalized forms of deliberation that does not pay due attention to the many forms and dynamics of participation. We contend that, by contrast, Sen's epistemology may be fruitful for the development of a critical sociology of democracy and suggest an agenda for empirical research on participation and deliberative practices.