The only protection as a historian is to institute a process of research and writing that minimizes the possibility of error. And that I have tried to do, aided by modern technology, which enables me, having long since moved beyond longhand, to use a computer for both organizing and taking notes.

Right now, American law bars the admission of aliens suspected of terrorist activity - but not of terrorist sympathies.

If the terrorists have the sympathy of people, it's much harder to find them. So we need people on our side, and that leads us to be responsible leaders of the world, show some concern with the problems.

The strength of democratic societies relies on their capacity to know how to stand firm against extremism while respecting justice in the means used to fight terrorism.

Touch is more important than arm strength. You want to really allow the receiver to run underneath the throw. It'll give you a little margin for error if you undershoot it a bit.

When terrorists attacked the symbols of our national unity and strength, they failed to realize that they were just symbols of our strength. The real strength of our nation comes from our people - not our buildings.

When it comes to tyrants, dictators and terrorists, strength and the threat of force is the only language they understand.

Confession of errors is like a broom which sweeps away the dirt and leaves the surface brighter and clearer. I feel stronger for confession.

Insincerity is always weakness; sincerity even in error is strength.

There are many who lust for the simple answers of doctrine or decree. They are on the left and right. They are not confined to a single part of the society. They are terrorists of the mind.

The law is an adroit mixture of customs that are beneficial to society, and could be followed even if no law existed, and others that are of advantage to a ruling minority, but harmful to the masses of men, and can be enforced on them only by terror.

Art and science have so much in common - the process of trial and error, finding something new and innovative, and to experiment and succeed in a breakthrough.

The scientific community should work as hard as possible to address major issues that affect our everyday lives such as climate change, infectious diseases and counterterrorism; in particular, 'clean energy' research deserves far higher priority. And science and technology are the prime routes to tackling these issues.

Science in the modern world has many uses; its chief use, however, is to provide long words to cover the errors of the rich.

Art has a double face, of expression and illusion, just like science has a double face: the reality of error and the phantom of truth.

Science can purify religion from error and superstition. Religion can purify science from idolatry and false absolutes.

In all science, error precedes the truth, and it is better it should go first than last.

Let both sides seek to invoke the wonders of science instead of its terrors. Together let us explore the stars, conquer the deserts, eradicate disease, tap the ocean depths, and encourage the arts and commerce.

The sad fact is that the same terrorist scenarios, if they occurred in five different States, there could be five different sets of responses to the American people. We need, at a minimum, a level of coordination on communicating threats to the public.

In a sad twist of fate, the bill to reauthorize the Patriot Act was debated on the floor of the House of Representatives the same day that terrorists struck again.

It is a historical error for those who were not there to just refer to August 28th as 'I Have a Dream' speech day. That is a real disservice to those who were there. It was a sad day. It was not a celebration environment.

I'm proud of my invention, but I'm sad that it is used by terrorists.

The closing of a door can bring blessed privacy and comfort - the opening, terror. Conversely, the closing of a door can be a sad and final thing - the opening a wonderfully joyous moment.

Terrorism can never be accepted. We must fight it together, with methods that do not compromise our respect for the rule of law and human rights, or are used as an excuse for others to do so.