By this I do not mean our tendency to misplace valuable objects, or our inability to recall the name of the boss’s dog, but the collective and cultural amnesia that overcomes any group of human beings who have long benefited from the inestimable blessings of civilization --- an amnesia first observed nearly eight hundred years ago by the Arab philosopher of history Ibn Khaldun, contemplating the rise and fall of those great human feats of organized life that we call by such terms as societies, states, and empires.

Forgetfulness occurs when those who have been long accustomed to civilized order can no longer remember a time in which they had to wonder whether their crops would grow to maturity without being stolen or whether their children would be sold into slavery by a victorious foe.

Even then it is necessary for the parents, and even grandparents, to have forgotten as well, so that there is no living link between the tranquility of the present generation and those dismal periods in which the world behaved very much in accordance with the rules governing Thomas Hobbes’s state of nature, where human life was "solitary, poore, nasty, brutish, and short."

When parents have forgotten what that world was like, they can hardly be expected to teach their children how it was or what one had to do in order to survive in it.

Civilized people forget that in order to produce a civilization there must be what the German sociologist Norbert Elias has called "the civilizing process," and that this process, if it is to be successful, must begin virtually at our birth, and hence many long years before the child can have any say about the kind of training he would have preferred.

They forget that the civilizing process we undergo must duplicate that of our neighbors, if we are to understand each other in our day-to-day intercourse. If you are taught to spit at a man who offers to shake your hand, and do when I offer you mine, we will not easily get along.

Civilized people forget how much work it is to not kill one’s neighbors, simply because this work was all done by our ancestors so that it could be willed to us as an heirloom.

They forget that in time of danger, in the face of the enemy, they must trust and confide in each other, or perish.

They forget that to fight an enemy it is necessary to have a leader whom you trust, and how, at such times, this trust is a civic duty and not evidence of one’s credulity.

They forget, in short, that there has ever been a category of human experience called the enemy.

That, before 9/ 11, was what had happened to us. The very concept of the enemy had been banished from our moral and political vocabulary. An enemy was just a friend we hadn’t done enough for yet. Or perhaps there had been a misunderstanding, or an oversight on our part --- something that we could correct.

Our first task therefore is to try to grasp what the concept of the enemy really means. The enemy is someone who is willing to die in order to kill you. And while it is true that the enemy always hates us for a reason, it is his reason and not ours. He does not hate us for our faults any more than for our virtues. He sees a different world from ours, and in the world he sees, we are his enemy. This is hard for us to comprehend, but we must if we are to grasp what the concept of the enemy means.

For Himmler, the Jewish children whom he ordered the SS to murder were the enemy because they would grow up to avenge the deaths of their fathers, who had been the enemy before them. We have killed their parents; they will want to kill our children. Hence we have no choice but to kill them first. The fact that they had done nothing themselves, and were incapable of doing anything themselves, was irrelevant.

This is how mankind has always thought of the enemy ---  as the one who, if you do not kill him first, will sooner or later kill you. And those who see the world in this way see it very differently from those who do not. This is the major fact of our time. 

We are caught in the midst of a conflict between those for whom the category of the enemy is essential to their way of organizing all human experience and those who have banished even the idea of the enemy from both public discourse and even their innermost thoughts.

But those who abhor thinking of the world through the category of the enemy must still be prepared to think about the category of the enemy. That is, even if you refuse to think of anyone else as an enemy, you must acknowledge that there are people who do in fact think this way.

Yet even this minimal step is a step that many of our leading intellectuals refuse to take, despite the revelation that occurred on 9/ 11. They want to see 9/ 11 as a means to an end and not an end in itself. But 9/ 11 was an end in itself, and that is where we must begin.

Why do they hate us? They hate us because we are their enemy.

THIS WAS THE REVELATION that came to Theodor Herzl when as a young newspaperman he had been sent to cover the Dreyfus trial in Paris during the 1890s. Herzl had been born in Budapest, a part of that great polyglot cosmopolitan Austro-Hungarian Empire in which Jews had done so remarkably well. As a student, he had thought that the solution to "the Jewish question" lay in complete assimilation of Jews, or what his biographer Alex Bein called their "disappearance without a trace in the ocean of the surrounding world."

But the reaction of the French crowds to the condemnation of Colonel Dreyfus shattered this illusion. The crowds had shouted: "Death to the Jews!" But why, Herzl asked himself, did they want death to all Jews, rather than death to the one Jew whom they believed guilty of treason? Herzl realized that even in France, one of the most liberal and civilized countries in the world, assimilated Jews were still hated for being Jews; and this meant that Herzl too was still hated for being a Jew. Not for having grandparents who were Jews, but for being a Jew himself.

This meant that being a Jew had nothing to do with how Herzl defined himself, but everything to do with how his enemy defined him. If his enemy wished to hate him because he was a Jew, he would, and Herzl’s own self- definition mattered to him not all --- a truth that was echoed by Karl Lueger, the virulently anti-Semitic demagogue who was elected mayor of Vienna in 1895, one year after Dreyfus’s arrest, and who was reputed to have said, "I decide who is or is not a Jew."

This disillusionment spelled the end of Herzl’s belief in the Enlightenment dream that all men could one day embrace in the spirit of universal cosmopolitanism and, ultimately, turned Herzl from the path of assimilation to Zionism. It is the enemy who defines us as his enemy, and in making this definition he changes us, and changes us whether we like it or not.

We cannot be the same after we have been defined as an enemy as we were before. That is why those who uphold the values of the Enlightenment so often refuse to recognize that those who are trying to kill them are their enemy. They hope that by pretending that the enemy is simply misguided, or misunderstood, or politically immature, he will cease to be an enemy. This is an illusion.

To see the enemy as someone who is merely an awkward negotiator or sadly lacking in savoir faire and diplomatic aplomb is perverse. It shows contempt for the depth and sincerity of his convictions, a terrible mistake to make when you are dealing with someone who wants you dead.

We are the enemy of those who murdered us on 9/ 11. And if you are the enemy, then you have an enemy. When you recognize it, this fact must change everything about the way you see the world. Once someone else sees you as the enemy, then you must yourself deal with this category of human experience, which is why societies that have enemies are radically different from societies that do not.

A society that lacks an enemy does not need to worry about how to defend itself against him. It does not need to teach any of its children how to fight and how not to run when they are being attacked by men who want to kill them. It does not need to appoint a single man to make instant decisions that affect the well-being of the entire community, and it does not need to train the community to respond to his commands with unthinking obedience.

But societies with enemies must do all of these things, and do them very well, or else they perish. Yet there is a problem with each of these various things that must be done to protect a society against its enemy. They are illiberal and they are at odds with those values that express the highest that civilized life has to offer --- tolerance, individual liberty, government by consensus rather than by fiat, and rational cooperation.

Thus it is not unnatural for those who prize such values to be reluctant to acknowledge the existence of an enemy serious enough to require illiberal measures, and they are correct to feel this way.

Those who argue that war is not the answer are almost invariably right, and if civilization can be said to inhere in any one single characteristic more conspicuously than in any other, it must certainly be in the preference for peaceful over violent methods of resolving conflict.

To be sure, civilization consists in more than this, but this more is always dependent on the prereflective certainty that the people you must deal with will not resort to force or threat or intimidation when they are dealing with you.

The first duty of all civilization is to create pockets of peaceableness in which violence is not used as a means of obtaining one’s objective; the second duty is to defend these pockets against those who try to disrupt their peace, either from within or from without. Yet the values that bring peace are the opposite values from those that promote military prowess, and this poses a riddle that very few societies have been able to solve and then only fitfully.

If you have managed to create your own pocket of peace --- and its inseparable companion, prosperity --- how will you keep those who envy you your prosperity from destroying your peace? There is only one way: you must fight back; if your enemy insists on a war to the finish, then you have no choice but to fight such a war. It is your enemy, and not you, who decides what is a matter of life and death.

Once you have accepted this reality, however, you are faced with the problem of how to fight. If your enemy is composed of men who will stop at nothing, who are willing to die and to kill, then you must find men to fight on your side who are willing to do the same.

Only those who have mastered ruthlessness can defend their society from the ruthlessness of others. This was the plight faced by the peasants in Kurosawa’s masterpiece The Seven Samurai and by the dirt farmers in the American remake, The Magnificent Seven. Men and women who knew nothing of battle, the impoverished peasants of a remote village found themselves at the mercy of a gang of ruthless bandits who each year came at harvest to steal what the peasant farmers had managed to eke from their soil. In their desperation the farmers turned to the seven samurai, all of whom had fallen on hard times.

But then, once the samurai had defeated the bandits, the question immediately arose in the peasants’ minds: "Now how do we rid ourselves of the samurai?"

Such has been the lot of most of mankind: a choice between the gangsters who come across the river to steal and the gangsters on this side of the river who do not need to steal because they have their own peasants to exploit. How else could it be? Given what we know of human nature, how could we expect there to be a government that wasn’t, in the final analysis, simply a protection racket that could make laws?

Yet this is not how Kurosawa’s movie ends. The samurai do not set themselves up as village warlords but instead move on, taking only the wages due them for their services. How was this possible? It was possible only because the samurai lived by a code of honor.

Codes of honor do not come cheap, and they cannot be created out of thin air upon demand. The fact that you need samurai and not gangsters is no guarantee that you will get them; indeed you will almost certainly not get them when you need them unless you had them with you all along.

A code of honor, to be effective when it is needed, requires a tradition that is blindly accepted by the men and women who are expected to live by this code. To work when it must, the code of honor must be the unspoken and unquestioned law governing a community: a law written not in law books but in the heart --- something like an instinct.

A code of honor cannot be chosen by us; it can only be chosen for us. For if we look on it as one option among many, then we may opt out of it at will. In which case the community will never be quite sure of us when the chips are down. All of which explains why those who subscribe to the values of the Enlightenment find the existence of the enemy so distressing.

The enemy challenges the Enlightenment’s insistence on the supremacy of pure reason by forcing us to respect those codes of honor whose foundation is far more visceral than rational, a fact that explains the modern intellectual’s hatred for such codes in whatever guise they lurk.

The enemy requires the continued existence of large groups of men and women who refuse to question authority and who are happy to take on blind faith the traditions that have been passed down to them.

The enemy necessitates the careful cultivation of such high-testosterone values as brute physical courage and unthinking personal loyalty to a leader.

The enemy demands instinctual patriotism and what Ibn Khaldun called "group feeling," that is, the sense of intense identification with one’s own people.

The enemy propels into postitions of command men who are accustomed to taking risks and who are willing to gamble with the lives of others, and shunts aside those who prefer the leisure of contemplation to the urgency of action.

Lastly, the enemy shatters the enlightenment’s visions of utopia, of Kant’s epoch of perpetual peace and of the end of history. And this is why so many American and European intellectuals refuse to acknowledge today even the possibility of the enemy’s existence, concocting theories to explain the actions of Al-Qaeda as something other than what they were.

This is also why all utopian projects are set either on a distant island or in a hidden valley: they must exist in isolation from the rest of the world, to keep even the thought of the enemy at bay. Otherwise they would have to deal with the problem of how to survive without abandoning their lofty ideals.

This is the problem that confronts us today. The ideals that our intellectuals have been instilling in us are utopian ideals, designed for men and women who know no enemy and who do not need to take precautions against him. They are values appropriate for a world in which everyone plays by the same rules, and accepts the same standards, of rational cooperation; they are fatally unrealistic in a world in which the enemy acknowledges no rule except that of ruthlessness.

To insist on maintaining utopian values when your society is facing an enemy who wishes only to annihilate you is to invite annihilation. And that is unacceptable.

The only solution is for us to go back and to unforget some of what we have forgotten, for our very forgetfulness is an obstacle to understanding the lessons of the past, so long as we insist on interpreting this past in ways that give comfort to our pet illusions.

We want to believe that civilization came about because men decided one fine morning to begin living sensible, peaceful, rational lives; we refuse to acknowledge what it cost to achieve even the first step in this direction. Unless we can understand this first step, none of the rest will make sense to us, and we will fail to see what is looming right in front of us.

The Greek way of expressing past and future differed from ours. We say that the past is behind us and the future is in front of us. To the Greeks, however, the past was before them, because they could plainly see its finished form standing in front of them: it was territory they had passed through and whose terrain they had charted. It was the future that was behind them, sneaking up like a thief in the night, full of dim imaginings and vast uncertainties. Nothing could penetrate the blackness of this unknown future except the rare flash of foresight that the Greeks called sophos, or wisdom.

Yet even these flashes of wisdom depended entirely on the capacity to remember what is eternal and unchanging --- which is precisely what we have almost completely forgotten.

The past tells us that there can be no end of history, no realm of perpetual peace, and that those who are convinced by this illusion are risking the survival of all that they hold dear.

The past tells us that there will always be an enemy as long as men care enough about anything to stake a claim to it, and thus enmity is built into the very nature of things.

The past tells us that the next stage of history will be a tragic conflict between two different ways of life, which both have much that is worthy of admiration in them but which cannot coexist in the same world.

But the past does not, and cannot, tell us how it will end this time.

That is why it is impossible simply to stand by and not take sides. No outcome is assured by any deep logic of history or by any iron law of human development. Individual civilizations rise and fall; in each case the fall was not inevitable but due to the decisions --- or lack of decision --- of the human beings whose ancestors had created the civilization for them, but who had forgotten the secret of how to preserve it for their own children. We are ourselves dangerously near this point, which is all the more remarkable considering how close we still are to 9/ 11.

It is as if 9/ 11 has become simply an event in the past and not the opening up of a new epoch in human history, one that will be ruled by the possibility of catastrophic terror, just as previous historical epochs were ruled by other possible forms of historical catastrophe, from attack by migratory hordes to totalitarian takeover, from warrior gangs to the threat of nuclear annihilation.

Our journey of recollection, must therefore begin with 9/ 11, for this was the moment when one epoch closed, and another opened.

With 9/ 11 commenced the next stage of history, one whose direction will be determined by how the world responds to the possibilities that it has opened up.

And yet, have we even begun to understand it?