To see the difference between traditional Anglo-American criminal jurisprudence and his proposed jurisprudence of prevention, he raises the great maxim of criminal law: better that ten guilty go free, than one innocent be wrongly convicted. That principle led our law to require proof beyond a reasonable doubt before conviction in criminal trials. Most of us agree with that standard.

But then Prof. Dershowitz updates the maxim thusly: "Is it better for ten possibly preventable terrorist attacks to occur than for one possibly innocent suspect to be preventively detained?" I would hunch that most people would not be willing to accept ten September 11th attacks (30,000 dead) in order to protect one innocent suspect from being locked up and questioned for a while.

Is it possible to go beyond such gut instincts and ad hoc decision making during a crises, and begin to develop a thoughtful set of standards for conduct in this dangerous new world? I don't know.

As Prof. Dershowitz observes, a jurisprudence develops slowly in response to generations, centuries of adjudicated events. But to the extent we recognize the need for it and start thinking systematically, to that extent we won't be completely hostage to the whim and discretion of a few men at moments of extreme stress.

At the minimum, an early effort at a jurisprudence of prevention would at least help in defining events. Consider the long and fruitless recent debate about the imminence of the danger from Saddam Hussein's Iraq, or the current debate on Iran's possible nuclear weapons. Under traditional international law standards they are both classic non-imminent threat situations: "early stage acquisition of weapons of mass destruction by a state presumed to be hostile."

But as Dershowitz points out, while the threat itself is not imminent, "the opportunity to prevent the threat will soon pass." Once they have the weapons it is too late.

Or, a low price in innocent casualties might soon pass. For instance, in 1981 when Israel bombed Iraq's nuclear site at Osirak, if they had waited much longer the site would have been "radioactively hot" and massive innocent civilian casualties would have been incurred from radioactive releases. It is simply not enough anymore to say a country violates the norm by acting in its ultimate, but not imminent, self-defense. We need new standards for a new age.

The new realities of unacceptable risk require new -- and lower-- standards of certainty before defensive action is permitted.

As we develop a jurisprudence of prevention, we increase the chance of justice and rationality being a bigger part of such crisis decisions that our presidents will be facing for the foreseeable future.

Dershowitz's sound, practical scholarship is commendable. But what I find heartening is the political fact that a prominent scholar of the left has finally entered into a constructive conversation about how to manage our inevitably dangerous WMD/terrorist infested future.

If such as Dershowitz and I can find common ground, there should be space there for a multitude. And from that common ground can grow a common plan for a common victory.

(Editor's Note: Professor Dershowitz's book is now on sale at Amazon.com for 34% off the cover price.)