Following Jürgen Habermas, Nicholas Garnham (1986) defines the public sphere as the network of media, educational, knowledge and opinion-forming institutions within civil society whose operation is conducive to the emergence of public opinion as a political power. Of those, the mass media are today perhaps the most powerful element of the public sphere. Peter Dahlgren (1987) makes the point that the components of the public sphere (including prominently the production of news, views and ideas in public circulation) derive from, mediate and serve to reproduce the existing social order. The more a society is integrated and united around the fundamental values of the existing social order, the more likely it is to have just one public sphere. The more divided it is, the greater the likelihood of the various groups within it creating institutions of will- and opinion-formation constituting different public spheres, taking fundamentally different stands on the legitimacy of the prevailing social order, and the desirability of its continued existence (cf. Negt and Kluge 1983; Downing 1984, 1988).
The moot question here is how large the group has to be and how extensive an institutional network with what social reach (or impact, which can be far greater, though more difficult to conceptualize and study) it has to generate for the purpose of opinion-formation and expression to be recognized as a full-fledged separate public sphere. Also, it can be assumed that apart from the question of the social order, ideas circulating within the different public spheres are likely to overlap to some extent. So, how much overlap can there be without the different public spheres merging