Today, in Zuccotti Park near ground zero in New York, in a field in Pennsylvania, and at the Pentagon in Washington, simple somber ceremonies will mark the anniversary of the attacks of September 11.

Six long years have passed since the twin towers fell, and the pain of that terrible morning, though receding, has not gone far away.

For those who live in Manhattan, in particular, the images conjured up by the very thought of 9/11 are almost too strong to bear.

Even today a plane flying too close over our heads is liable to cause a troubling murmur in the heart. The many films and television programs which have revived the dramas and the heroism of that day offer few attractions to those who lived it at first hand.

We saw sights and heard sounds that were so dreadful they have been seared deep in our brains and even the passage of time may never bring relief.

Today is a time to pause and remember those who died on that sunny morning in 2001, blithe victims of a dark and desperate ideology which seeks to return the world to a pre-industrial age. The victims came from all walks of life and from all around the world, as is the nature of the modern Western economy. We will remember them in silence and say a few words to express how grateful we were to have known them. We will then return to our quotidian duties far sadder than before.

This is not a moment for making narrow political points, and those who may seek to introduce partisanship in tomorrow’s ceremonies would be way off course. But politics must go on.

Our instant and universal response to the attacks on America was to fiercely defend our democracy and declare it too robust to be stifled by arbitrary acts of violence.

With a presidential election looming, some by their presence at the memorial services will hope to infer a message. So be it. It would be a victory for the terrorists if we were to abandon the crucial debate about how best to defend ourselves from tyranny.

Away from the celebration of the many lives needlessly lost we might find time to consider what has changed for us all in the last six years.

September 11, 2001, marked the end of an age of innocence and the abrupt beginning of an age of awareness. We have had to endure some trivial inconveniences. Many of our old carefree habits, particularly when traveling, have had to be abandoned in favor of openness and vigilance.

Some alterations are more profound. Some of our civil liberties have been curtailed, at least for now. Our patience as well as our constitution has been tested; neither has been found wanting.

These are small sacrifices compared to what is at stake. The Islamists would have us retreat from the world. They despise both the idea of free markets and the free market in ideas. They offer instead a cruel medieval world which would ignore all the liberating advances of the last 600 years. Their ideology cannot survive debate, which is why they abhor free speech and democratic institutions, and why they try to impose their intolerant notions on us by force. We have seen their like before, in the rise of the European dictators in the last century, and we learned then, almost too late, that such a persistent and savage assault upon our way of life cannot be appeased.

Unconditional surrender of our mortal enemies is the only guarantee of the freedoms we have long taken for granted. It is no hardship to be reminded of how fortunate we are to live in a free society; it is an honor and a pleasurable duty to have to defend the values we hold dear.

But we must beware scratching too hard at old wounds. It may be tempting to use today’s anniversary as an excuse to crawl back through the many decisions made before and since the attacks and focus upon those which were misguided or led to unintended consequences. It is, of course, everyone’s right to learn which lessons they prefer from our changed circumstances.

But in the months ahead we might do better to concentrate upon where we are, not where we have just come from, and to determine how best we might defend our way of life and who may be best to protect us from adversity.

For those with a sense of history, it is salutary to read Winston Churchill’s response to those who would dig over old ground and fight old battles rather than consider how best to confront the Axis dictators.

By the summer of 1940, with thousands of British troops being brought back to England in small boats from the Dunkirk beaches, Churchill had more reason than most to castigate those whose obduracy and blindness led them to ignore the dangers of Hitler and Mussolini.

He told Parliament on June 18, 1940: “There are many who would hold an inquest in the House of Commons on the conduct of the Governments — and the Parliaments, for they are in it, too — during the years which led up to this catastrophe. They seek to indict those who were responsible for our affairs. This also would be a foolish and pernicious process. There are too many in it. Let each man search his conscience and search his speeches. I frequently search mine. … Of this I am certain, that if we open a quarrel between the past and the present, we shall find that we have lost the future.”