Indeed, I suspect that what we say to each other, as Americans, is much more important on this anniversary than what we say to the jihadists. And what we ought to be telling each other today, on 9/11+6, is what we cannot not know.

We can't not know the identity of the enemy -- global jihadism -- and what that enemy believes. That is, we can't not know that global jihadism teaches that it is the duty of every Muslim to use any means available to advance the prospects of a world that acknowledges the sovereignty of Allah over all aspects of life and that lives under Shari'a law. (That the vast majority of the world's Muslims do not hold this view is both true and irrelevant.)

We can't not know that the jihadists read the history of the past 1,350 years through the prism of their theological convictions, not through the lens of Westrern progressivist concepts of how-things-will-turn-out.

We can't not know that the jihadists are carefully monitoring our cultural and political morale, eager to find the first signs of the weakness they detected in the late 1990s, which emboldened them to attempt an enormity like 9/11.

We can't now know that this struggle against global jihadism is for the long haul. The issues it poses will be on the next President's desk on January 21, 2009, and on the desk of every President for the foreseeable future. And we can't not know that anyone who doesn't understand this has no claim on the presidency.

We can't not know that inter-religious dialogue cannot be an exchange of banal pleasantries but must focus on helping Islam assimilate the positive achievements of the Enlightenment, including the separation of religious and political authority and the idea of religious freedom as an inalienable human right.

Finally, we can't not know that we ought to pray for the conversion of the hearts and minds of our jihadist enemies. I've heard very few such prayers these past six years. Their necessity is another thing we can't not know, six years after 9/11.