President Bush, in a speech at West Point in 2002.

"We cannot defend America and our friends by hoping for the best. We cannot put our faith in the word of tyrants, who solemnly sign non-proliferation treaties, and then systemically break them. If we wait for threats to fully materialize, we will have waited too long."

Since then the Bush doctrine of preemption has been put into effect in Iraq.

The doctrine raises interesting moral and philosophical issues. Why couldn't Marshall Dillon draw first, if the bad guy was clearly going to try to shoot him? Etiquette? Morals? Stupidity? Are nations in a "state of nature?" Or governed by law?

John and Ken distinguish between wars of aggression and of self-defense. Wars of aggression are bad. There are also preemptive wars, attacking before a known aggressor attacks, and wars of humanitarian intervention, attacking to help someone else. How sure does an attack have to be in order to morally justify preemptive self-defense? Ken introduces George Lucas, professor at the U.S. Naval Academy. Lucas says that the doctrine of preemptive self-defense is troubling in the modern political scheme. Lucas says that preemptive self-defense is warranted when the threat is imminent. Lucas says that the United Nations is ill equipped to address preemptive self-defense.

Where is the line between preemption and aggression drawn? Lucas says that preemption usually is a matter of hours or days. What gives the United States the right to attack Iraq when Al-Qaeda was the group that attacked? Lucas says that it is an interpretation of moral philosophy and lack of security provided by international laws that justify it. Must we always exhaust all alternatives before engaging in preemption? Is self-defense always morally right?

Michael Walzer proposed several criteria to determine if preemptive action is acceptable. Is preemption a self-defeating doctrine? If we attack others because we are worried that they will attack us, then won't other nations consider attacking us out of fear that we'll attack them too? Lucas says that the lack of an international police force creates problems for peaceful dealings with rogue nations. The United Nations was created during the Cold War, so it is inadequate to deal with many modern international problems. Do you have to know that an aggressor will attack or is it enough to fear it?

• Roving Philosohical Report (Seek to 05:00): Amy Standen interviews Charles Butterworth about Leo Strauss's philosophy and the doctrine of preemptive self-defense.

• Sixty Second Philosopher (Seek to 36:24): Ian Shoales gives a rapid overview of Niccolo Machiavelli's political philosophy.

• Conundrum (Seek to 48:45): Peter from Portland calls in to ask whether we can measure time? We use motion to measure time, a day is a rotation of the earth, and time to measure motion, miles per second. There also seems to be two kinds of time: objective time, as measured by clocks, and subjective time, as experienced by each of us.