G eorge W. Bush’s stubborn certitudes–about Iraq, about executive power, about the readiness of peoples everywhere to embrace democracy–have created a bull market for doubt, not least among conservatives. While there is still no shortage of assured conviction in American politics, it has become intellectually fashionable to place doubt at the heart of one’s political principles. Atlantic senior editor Andrew Sullivan has filled his blog–and his most recent book–with a call for a renewed place for doubt in conservative politics, drawing on everyone from Socrates to the twentieth-century British philosopher Michael Oakeshott. Likewise, many liberals, and in particular those hawks left soul-searching by their erstwhile support for the Iraq war, have turned to ancestral liberal doubters, most notably the theologian Reinhold Niebuhr, for intellectual succor.

This quest for alternatives to dogmatism has led in three directions. The first is toward common sense doubt–a renewed focus on the incompleteness and indeterminacy of data, and also on the vagaries of human judgment. The second ...