From Martin Brown’s blog:

Say I am walking down a street in a large city and come across a homeless person on the sidewalk, and I ask myself if that could have been my fate.  If I think that I could have been that person—except for different circumstances—then we share a common humanity.  Our differences are basically social.  If I say that I would never become such a person, then I take our social differences—class, race, religion, and so on—as essential. We have nothing in common. 
If we are all commoners, then our social differences are secondary.  If our social identity is absolute, then what we have in common is ignored, or denied.
So here is the dilemma.  We exist together in our separate and conflicting social identities.  No one can deny that.  Still, we exist together.  We cannot deny that either.  On the one hand, the process of socialization gives us our identity.  I am a white, middle class, mid-western (USA) male. Furthermore, my social relationships—husband/wife, parent/child, teacher/student, and so on—make me who I am. But that is true of others too.  One thing we have in common is the fact that each one of us has a particular social life.
This dilemma can be resolved through the civic.  The civic, as I understand it, refers to open and sharing conversations in which participants recognize one another as citizens—as members of the civic.  The civic does not erase the social barriers that separate us, but it allows us to see how others interpret them.  Sometimes, such mutual interpretation can turn our social conflicts into civic disagreements.
Disagreements arise because we live in different social worlds.  If our particular social identity totally defines us, then civic conversations are impossible. Civic conversations become possible only when we recognize our common humanity. At the same time, the full potential of our common humanity remains largely unrealized if we do not step up and participate in the process of constructing and evaluating civic arguments about how to improve our social life.