Cambridge, England

VICE PRESIDENT JOE BIDEN complains that he is being driven crazy because so many people are betting on America’s demise. Reports of it are not just exaggerated; they are, he insists, ridiculous. Like President Obama, he will not accept “second place” for the United States. Despite the present crippling budget deficit and the crushing burden of projected debt, he denies that the country is destined to fulfill a “prophecy that we are going to be a great nation that has failed because we lost control of our economy and overextended.”

Mr. Biden was referring in particular to the influential book “The Rise and Fall of the Great Powers” by Paul Kennedy, a British historian who teaches at Yale. Published in 1988, the book argues that the ascendancy of states or empires results from the superiority of their material resources, and that the wealth on which that dominance rests is eroded by the huge military expenditures needed to sustain national or imperial power, leading inexorably to its decline and fall. The thesis seems a tad schematic, but Professor Kennedy maintains it with dazzling cogency. In any debate about the development of the United States, one would certainly tend to side with the detached historian rather than the partisan politician.

All too often, however, students of the past succumb to the temptation to foretell the future. For reasons best known to himself, for example, the eminent British historian A. J. P. Taylor predicted that the Second World War would reach its climax in the Spanish port of Vigo. Equally preposterous in its way was Francis Fukuyama’s claim that the conclusion of the cold war marked the end of ideological evolution, “the end of history.”

When indulging his own penchant for prophecy, Paul Kennedy too proved sadly fallible. In his book, he wrote that Japan would not stagnate and that Russia, clinging to Communism, would not boom economically by the early 21st century. Of course, Professor Kennedy did not base his forecasts on runes or entrails or stars. He weighed the available evidence and extrapolated from existing trends. He studied form, entered suitable caveats and hedged his bets. In short, he relied on sophisticated guesswork. However, the past is a map, not a compass. It charts human experience, stops at the present and gives no clear sense of direction. History does not repeat itself nor, as Arnold Toynbee would have it, does it proceed in rhythms or cycles. Events buck trends. Everything, as Gibbon said, is subject to “the vicissitudes of fortune.”