When William the Conqueror commissioned a great survey of his English realm at Gloucester in 1085, the result was a work so thorough, fair, dispassionate, and wide-ranging that it seemed to the succeeding generations to have come from another world.

Up until the Depression, recession had a moral character: it was supposed to purge the body economic of the greed and excess that attends a business expansion.

Osama bin Laden, the Saudi-born revolutionary who is believed by most Arab and Iranian observers to be the inspiration of the attacks in New York and Washington, is the best known of the Islamic militants to have emerged in the past 20 years and the least difficult to fathom.

There are signs that the age of petroleum has passed its zenith. Adjusted for inflation, a barrel of crude oil now sells for three times its long-run average. The large western oil companies, which cartellised the industry for much of the 20th century, are now selling more oil than they find, and are thus in the throes of liquidation.

What holds an Arab leader in power is a mixture of violence and prestige. Both President Assad and King Hussein were felt to have defended Arab interests against the world. That, in the end, is more important than what they wear on their head.

A century ago, petroleum - what we call oil - was just an obscure commodity; today it is almost as vital to human existence as water.

Suicidal violence is not the exclusive property of the Muslim world. Suicide bombings were a tactic of nationalist struggles in 19th-century Europe and Russia, the far east during the second world war and the Vietnam war, and in modern Sri Lanka.