The terrorists who attacked Washington and New York on September 11 had the whole world to choose from, and they chose America. Why? Why do the attackers and their supporters hate us? What, exactly, do they hate? What can they hope to accomplish or prove? Who, exactly, are "they"? Some of the answers will be found in the newspapers. Others will be found in a book first published in 1945 by a philosopher named Karl R. Popper.

After World War II, Popper (1902-1994) settled in Britain, where, at the London School of Economics, he became Sir Karl and confirmed his standing as the 20th century's greatest philosopher of science. In 1945, however, he was laboring at an obscure university in New Zealand, where he'd been driven in 1937 by the threat of Nazi occupation of his native Austria. In March of 1938, as the Nazis rolled into his homeland, Popper began work on a comprehensive attack on the philosophers—Plato, Hegel, Marx—whose ideas he believed underpinned what later came to be called totalitarianism; he wrote through 1943. Those were the darkest years of the war and possibly of human civilization. The work that resulted was The Open Society and Its Enemies.

Quite a few commentators have said that even if Israel did not exist, Islamist extremists would still view the West in general, and the United States in particular, with anger and resentment and, above all, fear. Israel, according to this view, is the spark, not the fire. That is probably true. But what caused this explosion of wrath? The commentators offer a cacophony of explanations: unipolar American power, the historical roots and modern idiosyncrasies of Islam, the legacy of colonialism, blowback from U.S. policies, failing regimes' need for scapegoats, the pervasiveness of American cultural exports, and on and on. Yet most of us sense that none of those reasons quite touches bottom—that even taken together, they do not quite touch bottom. Something old and deep and in some respects hauntingly familiar is at work: something as old and deep and familiar as Plato, who stands at the very wellspring of Western philosophy. So suggests Popper.

For Popper, Plato was the first and greatest of all opponents of the open society. Plato holds that the things of this world are corruptible copies of perfect ideals, or Forms. A copy may be good or bad, but what is certain, Popper wrote, is that "every change, however small, must make it different, and thus less perfect, by reducing its resemblance to its Form." From that premise, argued Popper, Plato derives a deeply reactionary view of historical development: "All social change is corruption or decay or degeneration." (The italics, here and in other quotations, are in the original.) From that premise, in turn, a political conclusion directly follows: Plato "certainly believed ... in a general historical tendency toward corruption, and in the possibility that we may stop further corruption in the political field by arresting all political change."

Plato was not content to talk in generalities. Instead, he provided a blueprint of what he thought would be an ideal state. It is not a democracy. It is a martial, hierarchical regime headed by a philosopher-ruler—someone, Plato imagined, like himself, though recent experience suggests it is more realistic to imagine a cruder sort of philosopher, a Lenin or Mao or Khomeini, in charge. The regime's administrators and enforcers would be a military-bureaucratic elite of "guardians," to be specially trained (today we might say indoctrinated) and specially privileged.

Plato's brittle hierarchy remains stable and pure only so long as the administrative class remains uncorrupted and united; otherwise, the state will fall victim to decadence or infighting. The elites are thus not to mingle with the common people, so as not to go soft. Poetry, music, and other expressive arts are to be controlled by rigid censorship serving state interests, lest the guardians be distracted from their duties. Private property, private education, and even private families would also be distracting. Thus, writes Plato (in The Republic): "The state which is to achieve the height of good government must have community of wives and children and all education." To create this uncorrupted state, it will first be necessary, he says, for the rulers to clear the ground by expelling everyone above the age of 10 and then re-educating the children to erase the subversive influences of their parents.

In the 1940s, fascism and Stalinist Communism were uppermost in Popper's mind, but other regimes before and after have combined elements of Plato's vision. The Communists of Cambodia and Vietnam sought to kill or expel educated adults to clear the way for a fresh start. Soviet and Maoist Communism eliminated the antisocial distraction of private property. Plato's eugenic scheme to preserve the integrity of his ruling class found its echo in Nazi Germany. The strict control of music, poetry, and other expressive arts finds its expression in some of today's fundamentalist Islamic regimes.

Today, radical environmentalists crusade to stop the advance of biotechnology and commerce. Protesters against globalization—really against capitalism—take to the streets to rage against corporations and trade. The Rev. Jerry Falwell says that feminists, gays, abortionists, and "all of them who have tried to secularize America" made God turn his back on the United States so the terrorists could strike. Radical Islamists raise what they imagine to be God's own fist against the West.

It would be nutty to claim that these groups are linked, or that anti-globalists or environmentalists or Falwell had anything to with the 5,000 dead in New York. Trashing a Starbucks is certainly not the same as incinerating the World Trade Center. Yet the two impulses are related, and Popper put his finger on the kinship. What they have in common are two principles that Plato pioneered. One was: "Arrest all political change!" The other: "Back to nature!" (The "natural," remarked Popper, signified to Plato "what is innate or original or divine in a thing, while 'artificial' is that which has been later changed by man or added or imposed by him.")

In other words, today's anti-modern crusaders, different from each other though they undoubtedly are, all share Plato's horror of uncontrolled political and social change. They also share his belief that only a society that is "natural" (or godly in the one natural way, which amounts to the same thing) can justly stand.

Popper understood that Plato's instincts were deep and incorrigibly human: instincts grounded in the yearning for simplicity, stability, and the comforts of the known. He also understood that the open society stands unalterably opposed to Plato's vision. The open society replaces personal and tribal bonds with shifting and abstract ones; it replaces the comforts of apparent stability with the turmoil of all-too-obvious change.

And so the open society introduces what Popper called "the strain of civilization." He said: "This strain, this uneasiness, is a consequence of the breakdown of the closed society. It is still felt even in our day, especially in times of social change.... We must, I believe, bear this strain as the price to be paid for every increase in knowledge, in reasonableness, in co-operation, and in mutual help, and consequently, in our chances of survival." For, Popper said: "There is no return to a harmonious state of nature. If we turn back, then we must go the whole way-we must return to the beasts."

Such a return, he felt in 1945—in the wake of the Nazi calamity and with Stalin's empire glowering over the horizon—was a real possibility. "We can return to the beasts," he said. "But if we wish to remain human, then there is only one way, the way into the open society. We must go on into the unknown, the uncertain and insecure, using what reason we may have to plan as well as we can for both security and freedom."

Although Popper's reading of Plato was and remains controversial, his reading of society appears sounder than ever. In the face of the open society's irrepressible effervescence and astonishing durability, the followers of Plato are pushed ever further to the margins of the world. They see the eddies of uncontrolled change and spontaneous creativity lapping at their ankles. In the long run, there is no contest; but in the short run, there is always a fight.

That is why they lash out today in the name of Islam and will lash out in some other name tomorrow and for centuries hence. It is why President Bush is right to say that the battle will be a long one—though he means hundreds of days, and the reality is more like hundreds of years. It is why he is right to say that the argument is about freedom—freedom from the tyrannies of Platonic overlords, freedom to build and inhabit a fluid, creative culture. And it is why the open society will prevail.

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