Love and war have mingled human populations for eons. Even seeming isolates are hardly homogeneous. No population remains untouched by the genetic markers of panmixia. So with all our ethnic diversity, we humans remain one race. The branches of our language tree attest to eons of migration, commerce, and congress that antedate our written records. We seem fated to live together, and the rapid pace and broad franchise in our travels and interactions today, complemented by the human penchant for settling down in new surroundings, only raise to new intensity the salient question of this book: how we can live together with integrity.

Cultural and intellectual diversity have long prompted claims in behalf of skepticism and relativism. But the claims are specious: The fact of differences does not steal the warrant from all commitments or confirm the equal soundness of just any. Still less does it make differences unreal – as to derive not-p from p. Yet powerful pragmatic worries urge us to deny deep differences with one another, or give up all claims to truth, or concede that no way of thinking or living is better or worse than the rest. Otherwise, we are told, we are doomed to endless conflict, to bootless bloodshed, and ultimate self-destruction.