Here's a brief summary of part of what I'm going to say.
Many have suggested that the relation between the two concepts is insufficiently researched. Here I would like to 1) suggest two reasons why this might be so, 2) propose a rather simple model that might clarify the relation, and 3) briefly discuss some conclusions that might be drawn. In particular, since some theorists seem to be suggesting that the idea of public space is more suited to a radical politics open to the excluded or disadvantaged than that of the public sphere, I will try to evaluate that claim and indicate in what ways it might hold true.
1. Why the confusion?
To begin with, the public sphere is not at all an un-spatial concept. Habermas cannot be accused of neglecting the physical places or mediums in which the public sphere has developed - private homes, for instance, or coffeehouses, salons, assemblies, street, theatres, or newspapers. What is true is that the public sphere is not necessarily linked to any particular place or medium. It is also true that the relation to space has become further blurred by so-called globalization (and the growth of "diasporic public spheres", "transnational public spheres", "global public sphere moments" etc). The indeterminate relation to space is, I suggest, one important reason for the confusion regarding the relation between the concepts of the public sphere and public space.
To at least begin to clarify the confusion, I will argue as follows. Although not necessarily linked to any particular physical space, the public sphere can surely be described as a social space - a particular kind of social space characterized by political deliberation about common affairs. Using a concept of space that is socially rather than physically defined should be fine. As I will show, concepts of public space are in fact also usually socially defined.
A second reason for confusion is that there are two kinds of theories of public space. Both use the term "public space" but they do so in opposite ways.
On the one hand, there are theorists of urban sociability like Erwin Goffman, Georg Simmel, Richard Sennett, Lynn Lofland, or Jane Jacobs. What they have in common is that they all link ”publicness” to concrete urban space. But there is no real link to the public sphere, to politics. What matters is that people are visible to each other, not that they talk or discuss. What they research is how strangers behave when they share a space where they are mutually visible to each other. What sustains "publicness" is the system of norms that regulates this interaction. Goffman's "civil inattention" is a well-known example of this norm-guided behavoir. Jane Jacob's Hudson Street "ballet" is another example. The formal etiquette between strangers which Sennett sees as so crucial to the publicness of the ancient régime is a third.
On the other hand, there are scholars like Jacques Rancière, Don Mitchell or Bruce d'Arcus, whose main interest is in "dissent public space" (this is d'Arcus' term). I've already discussed their idea of public space in a previous blog entry ("Public Space and Public Sphere: Notes on Reading Don Mitchell"). Common to them is that they see publicness as arising through acts that manifest or visibilize dissent. If the theorists of urban sociability see publicness are maintained by an intricate system of norms, the theorists of dissent see it as erupting when the norms are disrupted.
The former group of scholars associate public space with norms of bracketing - or systematically disregarding - differences in status among people. Where all are strangers, there is no high or low. We refrain for inquiring to deeply into the background of the strangers we meet. By doing so, we maintain the semblance that everyone is equal. The second group of scholars, by contrast, associate publicness with un-bracketing, with the "uncivil" taking or occupation of place where injustice is visibilized. Rather than bracketing marginalization, oppression or status differences, they are brought out into the open.
2. Contention and bracketing: a model
A solution requires that we start, not from the dichotomy of "sphere" and "space", but by investigating two dimensions of "publicness" which I believe are more fundamental.
As I argue in "Public Space in Recent Japanese Political Thought and Activism: From the Rivers and Lakes to Miyashita Park" (forthcoming in Japanese Studies 31:3, December 2011), two dimensions are constitutive of the public in classical theorists like Habermas and Arendt: verbal contestation and the bracketing of dependencies and inequalities in wealth and status. Typically, deliberations in the public sphere rest on the presence of both of these two dimensions. Deliberation can be seen as a form of communication in which contestation is moderated by the norms of bracketing, which are necessary in order to create a semblance of equality among the participants. Bracketing is thus ambivalent: it is thanks to bracketing that egalitarian arenas can be created, but it also prevents real inequalities in wealth, status and power from being openly thematized and challenged.
To summarise, the public is not only a realm of free and open communication or debate, but also an arena in which important parts of social life are systematically bracketed in order to create a semblance of equality among participants. This means that the public – against the commonsensical view – must be viewed not only as an arena of debate and communication. It is also constituted by a certain silence, a ‘bracketing’ that is needed to prevent it from dissolving back into the ‘real’ world.Interestingly, challenges to the exclusivity of the mainstream public sphere have come from two directions, one emphasizing more thoroughgoing forms of bracketing (Karatani Kôjin's defence, in Transcritique, of bracketing as crucial to a Kantian public can be seen as one version of this) and another emphasizing more unrestrained forms of contestation (here a good example is Nancy Fraser's subaltern counterpublics and her advocacy of "unbracketing").
An important point here, which I feel it is necessary to stress in order to grasp the function of bracketing more fully, is that there are multiple public with alternative norms of bracketing. Bracketing thus openates also in the subaltern counterpublics. There's a sociological classic, The Hobo (by Nels Anderson), that provides a wonderful insight into the camps (or "jungles") of the homeless people in early 20th century America. Just as the Simmelian salons or Habermasian coffeehouses, these were egalitarian and "democratic" arenas. People exchanged information and told stories over the fire. But they never inquired too deeply into a person's name or previous life. Just as in the salons and coffee houses, they bracketed each other's background.
Let us now try relating the various theories of public space and public sphere to these two dimension.
The "classical" theories of the "public sphere" (or "public realm") are found in the upper right quadrant, i.e. they are theories that stress both bracketing and contention. Grasped from its spatial aspect, we might call it "space for deliberation".
We can also observe that the most influential theories stressing "public space" fall into two distinct groups, which have very little in common.
So we see: the classical theories are not radically divorced from the theories of public space. They share the stress on dimensions such as bracketing or contestation. Hence the first difficulty of separating and counterposing "public sphere" and "public space" in a clearcut fashion.
The second difficulty stems from the fact that theories of public space are not uniform. "Public space" is a catchword for very heterogeneous conceptions. These tend to fall into two camps, which are mutually more opposed to each other than either are to the theories of the "public sphere".
To summarize: the reason that the relation between public sphere and public space is so hard to clarify is that the public sphere arises in the convergence of bracketing and contestation, i.e. that it requires a mixture of both elements. Conceptions of public space arrange themselves in two compartments on either side of this.
3. Some consequences
Theories of public sphere have been criticized for being exclusive, hierarchical, and too restrictive. Some - most explicitly Don Mitchell - seem to propose "public space" as a more radical notion, more open to the excluded. What conclusions can we draw?
Well, public space theory exists in two forms which both "radicalize" certain aspects of the "public sphere". Some point to spaces that provide refuge from "real" social status, others to spaces for contesting and renegotiating the order.
At whichever of these two senses of public space one looks, one finds a political significance geared to those excluded from or disadvantaged in the politics of the public sphere. Are we then entitled to conclude that "public space" is more suited to be the focal point of a radical politics than the "public sphere"? The correct way to put it is surely that public space is not inherently radical in itself, but rather a crucial and irreducible element in all politics. What goes beyond the regular politics of the public sphere is not space in itself, but rather acts that use space to unbracket or visibilize inequalities or to construct arenas based on alternative forms of bracketing.