Behind every act by the government there lies a guiding principle that grounds the deed in either some ideological or moral setting.

And so, it serves as no surprise that behind President George W. Bush’s decision to invade Iraq—the act which, above all, will linger in people’s memories and determine his legacy—is an endorsement of the ideology of preemption and preemptive warfare.

However, preemption differs from other ideological underpinnings because it doesn’t as neatly cut across the partisan divide—John Kerry did originally support the invasion, and Democrats generally support humanitarian preemption.

Among many Democrats, the stock argument is that Bush made his decision capriciously, and they remain unconvinced that he did his due diligence when deciding that preemption was right in Iraq’s case.

But deciding when preemption is right or wrong is tricky business and creating a universal formula is nearly impossible—at least that’s what Frankfurter Professor of Law Alan M. Dershowitz argues in his latest book, “Preemption: A Knife That Cuts Both Ways.”

While wisely refraining from offering a calculus for preemption, Dershowitz deftly attacks the issue.

He teams his characteristically deep historical understanding with his reliable legal acumen to produce a forward-looking proposal for the jurisprudence of preemption.

After looking at conflicts in Iraq, Israel, and Iran in light of preventive foreign policy, Dershowitz finally offers a plan, shifting the question from whether preemption is appropriate in the first place to how we judge the results of preemptive policy in hindsight.

And this is really what we need him for.

Dershowitz, considered one of the nation’s top legal minds, is capable of applying legal precedent and practical application to contextualize these international conflicts, far beyond our own interpretations of news and speechs on foreign policy.

The real challenge for Dershowitz’s text is to distinguish itself from his more than 20 other intellectual treatises and publications.

Unfortunately, his legal analysis does not provide enough novel insight to make “Preemption” stand out.

The last section, and the book on the whole, is solid but not extraordinary. Dershowitz crafted the book to be agreeable but not risky, and as a result, “Preemption” fails to make any really lasting statements.

Dershowitz is conscious of how fickle people are about preemption and how slippery the concept is itself.

He prefaces many of his substantive points by writing that a categorical opinion or response to preemption is impossible and foolhardy, and he constantly reminds us that there is no one right answer.

With warnings against treating preemption as a “yes or no, black or white, legal or illegal” and repeated assertions that a jurisprudence cannot be created flawlessly in one try, Dershowitz is resigned to treating this work not as a landmark treatise on preemption but as a first building block.

In the end, the progressive tone to “Preemption” and its recognition that it is part of an evolving literature on the issue proves an asset. Dershowitz appropriately situates himself as a guide, not an authority.

The book’s lucid and plain language matches its fundamental nature as a guidebook and allows Dershowitz to walk the reader through his own thoughts on preemptive policy in a methodical, unpretentious way.

He knows that the concept is tough to grapple with and before he can pontificate—which he rarely does here—he must first explain and explore.

Dershowitz does suggest a baseline for deciding when preemption is right. His sketch for a formula pits the seriousness of an incident and its likeliness without preemption against the harm caused by preemption and its likelihood of success.

This basic comparison allows governments to decide whether the harm itself outweighs the harms inherent to preemption.

But, “Preemption,” for its intentional caution and recognition that it is not the final word on its titular topic, seems to be stuck in purgatory.

Though Dershowitz needs to avoid sounding authoritative and values discussion over definitive statement, “Preemption” seems doomed to be forgotten.

While Dershowitz does roughly outline a plan and a jurisprudential system, he himself calls it only “suggestive,” a rather weak endorsement of one’s own work.

Rather than being a groundbreaking first work on the topic, Dershowitz settles for just the “first work” part, serving up a dulled analysis of what might have been a sharper knife.

—Staff writer Benjamin L. Weintraub can be reached at bweintr@fas.harvard.edu.

Preemption: A Knife That Cuts Both Ways
By Alan M. Dershowitz
W.W. Norton
Out Now