In this winter of their discontents, nostalgia for Ronald Reagan has become for many conservatives a substitute for thinking. This mental paralysis - gratitude decaying into idolatry - is sterile: Neither the man nor his moment will recur. Conservatives should face the fact that Reaganism cannot define conservatism.

That is one lesson of John Patrick Diggins' new book, "Ronald Reagan: Fate, Freedom, and the Making of History." Diggins, a historian at the City University of New York, treats Reagan respectfully as an important subject in American intellectual history. The 1980s, he says, thoroughly joined politics to political theory. But he notes that Reagan's theory was radically unlike that of Edmund Burke, the founder of modern conservatism, and very like that of Burke's nemesis, Thomas Paine. Burke believed that the past is prescriptive because tradition is a repository of moral wisdom. Reagan frequently quoted Paine's preposterous cry that "we have it in our power to begin the world over again."