How do real individuals live together in real societies in the real world? What binds societies together and how can these social orders be structured in a fair way? This book addresses this central paradox of modern life. Feelings for others—the solidarity that is ignored or underplayed by theories of power or self-interest—are at the heart of this novel inquiry into the meeting place between normative theories of what we think we should do and empirical studies of who we actually are. The book demonstrates that solidarity creates inclusive and exclusive social structures, and shows how they can be repaired. It is not perfect, it is not absolute, and the horrors which occur in its lapses have been seen all too frequently in the forms of discrimination, genocide, and war. Despite its worldly flaws and contradictions, however, solidarity and the project of civil society remain our best hope—the antidote to every divisive institution, every unfair distribution, and every abusive and dominating hierarchy. A grand and sweeping statement, the book is a major contribution to our thinking about the real but ideal world in which we all reside.