The Kingdom Catholics, corresponding to those we call progressive, were "exhilarated by the council's embrace of modernity" and "see our church as primarily the people of God on pilgrimage toward the kingdom."
"The Christ whom they cherished," he writes, "was the one who overthrew the boundaries between human beings, who touched lepers, reached out to foreigners, and gathered us into the people of God." Theirs was "an outward-looking theology" that was "rooted in experience" and emphasized "liberation." Kingdom Catholics look to the council era as a time when "everything seemed possible."
The Communion Catholics view the same period as the equivalent of "ecclesiastical urban planning, tearing up our neighborhood." This group, in which Pope Benedict XVI is the leading figure, insists that the church "stand firm in the proclamation of our faith."
Radcliffe explains the skepticism toward modern ideas: "If one embraces the language of modernity too uncritically, then we are likely to lose our identity and be absorbed without a trace. ... We must not let ourselves be assimilated to the world. We must not be afraid to underline what is distinctive about our faith, otherwise we will disappear."
While the Communion Catholics can fairly be seen as conservative, their views do not always conform to what most American conservatives believe. Benedict, for example, was tough on the injustices of capitalism, a view consistent with a traditionalist critique of materialism.
Radcliffe, who insists that Kingdom and Communion Catholics need each other, would not pretend his categories cover all of the challenges facing the church. The pedophilia scandal has undermined the leadership's authority in ways that cut across theologies.
Where Radcliffe is powerfully right is in seeing that both contending parties are now experiencing a kind of homelessness - and for this lost sense of belonging, they tend to blame each other.
The Kingdom side sees the Communion side abandoning the promise of Vatican II. Communion Catholics see the Kingdom Catholics as too willing to undercut Catholic identity. In the coming conclave, Communion Catholics have the votes. Kingdom Catholics are hoping the Holy Spirit will spring a surprise.
While it's a mistake to draw too many parallels between the controversies inside Catholicism and the fights within U.S. politics, I'm struck by how helpful Radcliffe's emphasis on homelessness is in explaining America's current struggles.
Liberals see conservatives as trying to roll back the advances in economic justice and civil rights wrought by a century's worth of progressive policies - programs and laws that draw their inspiration from the nation's founding declaration that all are created equal. Conservatives insist that they are the champions of "the real America" and the true guardians of the creed embodied in our nation's founding documents. Each accuses the other of trying to wreck what makes our country great.
I am inclined, with Radcliffe, to believe we should celebrate rather than mourn our intellectual tensions. But living with those tensions requires far more trust than we now seem capable of managing. What I do know is that throwing one side out of the house is not a solution to homelessness.
E.J. Dionne is a Washington Post columnist. E-mail him at firstname.lastname@example.org.