The article analyses the common notion that the consumer society is a reflection of those principles in the market that also provide the ideas of democracy and liberal constitutionalism with legitimacy in the political realm. The inalienable right to self-development and self-determination makes the individual the starting and ending point of life, rendering all spheres of market and society a ‘republic of choice’. But if consumer society shares the essentials of liberal constitutionalism and the rational, processual nature of democratic representation, then its ontology needs to be investigated for the same reason and in the same manner as legal and political philosophy dissects the legitimacy and validity of the parliamentary institutions of modern democracy. Just as in the political philosophy of the constitutional structure of the democratic state, the question of who is sovereign is key to understanding the ontology of consumer society. But rather than simply placing sovereignty into the hands of the independent, self-determined consumer, the earliest ontologists of the consumer society took recourse to medieval political theology and presented the consumer market as a new corpus mysticum. Thus, it is medieval political theology, not modern liberal thought, which provided for an ontologization of the consumer. This, in turn, directly pertains to the questions of the legitimacy of consumer society per se, of consumer decisions in particular and of their sources of legitimacy.