Bernard Lewis came to the New World in the nick of time. Fate -- or, more appropriately, history -- decreed his American journey and the direction it would take. The historian, who will turn 90 in a handful of days, had come to Princeton from London, at the age of 58, in 1974, to do the work of Orientalism which had gained him scholarly renown. But there would be no academic seclusion for him in the years after. The lands of Islam whose languages and cultures he knew with such intimacy would soon be set ablaze. And his adopted country, the bearer of the imperial mantle shed by his own Britannia, would in time make an honored place for him, and all but anoint him its guide into those burning grounds of the Islamic world. He would become the oracle of this new age of the Americans in the lands of the Arab and Islamic worlds.

In the normal course of things, America is not a country given to excessive deference to historians and to the claims of history, for the past is truly a foreign country here. But the past quarter century was no normal time, and Mr. Lewis no typical historian. He knew and worked the archives, it is true; and he mastered the languages of "the East," standing at the peak of his academic guild. But there is more to him than that: He is, through and through, a man of public affairs. He saw the coming of a war, a great civilizational struggle, and was to show no timidity about the facts of this war. "I'll teach you differences," Kent says to Lear. And Mr. Lewis has been teaching us differences. He knew Islam's splendor and its periods of enlightenment; he had celebrated the "dignity and meaning" it gave to "drab impoverished lives." He would not hesitate, then, to look into -- and to name -- the darkness and the rage that have overcome so many of its adherents in recent times.

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We anoint sages when we need them; at times we let them say, on our behalf, the sorts of things we know and intuit but don't say, the sorts of things we glimpse through the darkness but don't fully see. It was thus in the time of the great illusion, in the lost decade of the 1990s, when history had presumably "ended," that Bernard Lewis had come forth to tell us, in a seminal essay, "The Roots of Muslim Rage" (September 1990), that our luck had run out, that an old struggle between "Christendom" and Islam was gathering force. (Note the name given the Western world; it is vintage Lewis, this naming of worlds and drawing of borders -- and differences.) It was the time of commerce and globalism; the "modernists" had the run of the decade, and a historian's dark premonitions about a thwarted civilization wishing to avenge the slights and wounds of centuries would not carry the day. Mr. Lewis was the voice of conservatives, a brooding pessimist, in the time of a sublime faith in things new and untried. It was he, in that 1990 article, who gave us the notion of a "clash of civilizations" that Samuel Huntington would popularize, with due attribution to Bernard Lewis.

The rage of Islam was no mystery to Mr. Lewis. To no great surprise, it issued out of his respect for the Muslim logic of things. For 14 centuries, he wrote, Islam and Christendom had feuded and fought across a bloody and shifting frontier, their enmity a "series of attacks and counterattacks, jihads and crusades, conquests and reconquests." For nearly a millennium, Islam had the upper hand. The new faith conquered Syria, Palestine, Egypt and North Africa -- old Christian lands, it should be recalled. It struck into Europe, established dominions in Sicily, Spain, Portugal and in parts of France. Before the tide turned, there had been panic in Europe that Christendom was doomed. In a series of letters written from Constantinople between 1555 and 1560, Ogier Ghiselin de Busbecq, imperial ambassador to the court of Suleyman the Magnificent, anguished over Europe's fate; he was sure that the Turks were about to "fly at our throats, supported by the might of the whole East." Europe, he worried, was squandering its wealth, "seeking the Indies and the Antipodes across vast fields of ocean, in search of gold."

But Busbecq, we know, had it wrong. The threat of Islam was turned back. The wealth brought back from the New World helped turn the terms of trade against Islam. Europe's confidence soared. The great turning point came in 1683, when a Turkish siege of Vienna ended in failure and defeat. With the Turks on the run, the terms of engagement between Europe and Islam were transformed. Russia overthrew the Tatar yoke; there was the Reconquista in the Iberian Peninsula. Instead of winning every war, Mr. Lewis observes, the Muslims were losing every war. Britain, France, the Netherlands and Russia all soon spilled into Islamic lands. "Europe and her daughters" now disposed of the fate of Muslim domains. Americans and Europeans may regard this new arrangement of power as natural. But Mr. Lewis has been relentless in his admonition that Muslims were under no obligation to accept the new order of things.

A pain afflicts modern Islam -- the loss of power. And Mr. Lewis has a keen sense of the Muslim redeemers and would-be avengers who promise to alter Islam's place in the world. This pain, the historian tells us, derives from Islam's early success, from the very triumph of the prophet Muhammad. Moses was not allowed to enter the promised land; he had led his people through wilderness. Jesus had been crucified. But Muhammad had prevailed and had governed. The faith he would bequeath his followers would forever insist on the oneness of religion and politics. Where Christians are enjoined in their scripture to "render unto Caesar the things which are Caesar's and unto God the things which are God's," no such demarcation would be drawn in the theory and practice of Islam.

It was vintage Lewis -- reading the sources, in this case a marginal Arabic newspaper published out of London, Al-Quds Al-Arabi, in February of 1998 -- to come across a declaration of war on the United States by a self-designated holy warrior he had "never heard of," Osama bin Laden. In one of those essays that reveal the historian's eye for things that matter, "A License to Kill," Mr. Lewis would render into sublime English prose the declaration of bin Laden and would give it its exegesis. The historian might have never heard of bin Laden, but the terrorist from Arabia practically walks out of the pages of Mr. Lewis's own histories. Consider this passage from the Arabian plotter: "Since God laid down the Arabian Peninsula, created its desert, and surrounded it with seas, no calamity has ever befallen it like these crusader hosts that have spread in it like locusts, eating its fruits and destroying its verdure; and this at a time when the nations contend against Muslims like diners jostling around a bowl of food. . . . By God's leave, we call on every Muslim who believes in God and hopes for reward to obey God's command to kill the Americans and plunder their possessions whenever he finds them and whenever he can."

Three years later, the furies of bin Laden, and the cadence and content of his language -- straight out of the annals of older wars of faith -- would remake our world. There would come Mr. Lewis's way now waves of people willing to believe. They would read into his works the bewildering ways and furies of preachers and plotters and foot soldiers hurling themselves against the order of the West. Timing was cruel -- and exquisite. The historian's book "What Went Wrong?" was already in galleys by 9/11. He had not written it for the storm. He had all but anticipated what was to come. This diagnosis of Islam's malady would become a best seller. In a different setting, Mr. Lewis had written of history's power. "Make no mistake, those who are unwilling to confront the past will be unable to understand the present and unfit to face the future." We were witnessing an epic jumbling of past and present. It was no fault of this historian that we had placed our bet on the death of the past.

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Mr. Lewis has lived a long and engaged life, caught up in the great issues of war and diplomacy -- and may he be with us as far as the eye can see, as long as life and good health permit. Some of his detractors, with an excessive belief in his talismans, have attributed to the historian all sorts of large historical deeds. For some, he is the godfather of the accommodation of years past between Turkey and Israel. For others, he inspired the Iraq war, transmitting to Vice President Dick Cheney his faith in the Iraq campaign as the spearhead of an effort to reform the Arab world. (It will, of course, help confirm this view that Mr. Cheney is set to speak to a conference today, hosted by the World Affairs Council of Philadelphia, in honor of Mr. Lewis.) In more recent writings on the historian, George W. Bush's "diplomacy of freedom" in Arab-Muslim lands is laid at Mr. Lewis's doorstep. The president was seen, in one account, with a marked-up copy of a Lewis article. We have come to a great irony: the conservative Orientalist holding out democratic hope for Iraq and its Arab neighbors, while his liberal critics assert the built-in authoritarianism of the Arab political tradition.

For Bernard Lewis, there is something now of the closing of a circle. As a young man, he had been on His Majesty's service during the Second World War, working for British intelligence between 1940 and 1945. The young medievalist had been pressed into modern government work, and that experience had given him his taste for contemporary political affairs. This new war is something of a return to his beginnings. For an immensely gregarious man of unfailing wit and personal optimism, a darkness runs through his view of the future of the Western democracies. "In 1940, we knew who we were, we knew who the enemy was, we knew the dangers and the issues," he told me when I pressed him for a reading of the struggle against Islamic radicalism. "In our island, we knew we would prevail, that the Americans would be drawn into the fight. It is different today. We don't know who we are, we don't know the issues, and we still do not understand the nature of the enemy."

The Muslim Brotherhood in Egypt, which once translated one of Mr. Lewis's books into Arabic, said that his book was "the work of a candid friend or an honest enemy." Either way, the Brotherhood said, it was the work of "someone who disdains falsification." And this, to me and to his countless readers, runs to the core of this historian's craft -- the aversion to falsification. He has been, always, a man of his own civilization and convictions -- a fact that accounts for the deep reservoirs of reverence felt for him in many Muslim and Arab lands. In the American academy, he may be swimming against the currents of postmodernism and postcolonial history; he has given up his membership in the Middle East Studies Association, of which he had been a founding member. But countless Arab and Iranian and Turkish readers recognize their tormented civilization in what he has written. They know that he has not come to the material of their history driven by bad faith, or by a desire for dominion. They take him at his word, a man of the Anglo-Saxon world, convinced that the ways of the West today carry with them the hopes of other civilizations. In one of his many splendid books, "Cultures in Conflict: Christians, Muslims, and Jews in the Age of Discovery," he gave voice to both his fears and to his faith. "It may be that Western culture will indeed go: The lack of conviction of many of those who should be its defenders and the passionate intensity of its accusers may well join to complete its destruction. But if it does go, the men and women of all the continents will thereby be impoverished and endangered."

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Edward Gibbon once called the historian's "I" the "most disgusting of pronouns." In the main we see very little of that pronoun in Mr. Lewis's work. But in the academy he belongs to the ages. He is the peer, and inheritor, of the great Western scholars of Islam -- the Hungarian Ignaz Goldziher (1850-1921), the Dutchman Christiaan Snouck Hurgronje (1857-1936), the Frenchman Louis Massignon (1883-1962), the British Thomas Arnold (1864-1930), and Mr. Lewis's own teacher, Sir Hamilton Gibb (1895-1971). Mr. Lewis took to the East to understand his own world, because, as he tells us, Western civilization "did not spring like Aphrodite from the sea foam." He wanted to get to the mainsprings of Western civilization.

I shall set aside the ban on that "most disgusting of pronouns." I came to know Bernard Lewis the year he made his passage to America, on the Princeton campus. I was then at the beginning of my academic career, justifiably obscure and anxious. Mr. Lewis was one of the academic gods. I approached him with awe. But his grace was our bridge. I was of the old world he studied; he was keen to know the name of my ancestral village in southern Lebanon. I told him it was an obscure place without history, and gave him its name. He offered me an invitation to examine his archives, and said that he had the land deeds of that remote hamlet. It has been like this with Bernard Lewis: We travel by the light of his work. He weaves for us a web between past and present, and he can pick out, over distant horizons, storms sure to reach us before long.

Mr. Ajami, Majid Khadduri Professor at Johns Hopkins University's School of Advanced International Studies, is author of "The Foreigner's Gift: The Americans, the Arabs, and the Iraqis in Iraq," forthcoming from the Free Press in July.