Anyone who had to be well versed on arms control during the Cold War knows there are few topics more important, and few more stultifying. The mind spun as it grappled with SALT, START, NPT, CTBT, payloads, drawdowns and MAD -- mutually assured destruction.

United Nations weapons experts in Iraq are heading out today on their first inspection missions, and I fear we're in for another megadose. I'm reading about verification, monitoring, precursors, complexes and test sites. Is there an analogy that makes it easier to think about the concepts involved?

Suppose it's wartime, and rationing is in effect, and the government is requisitioning food supplies. Hoarding is a crime. You hear a guy down the street has a secret supply of milk he's willing to sell at three times the normal price. You tip off the police; they decide to investigate.

Their first problem is access. They have to get into the house, get the fridge open and check out other likely hiding spots, all without the neighbour having a chance to dump any contraband or stash it somewhere else.

Next comes verification. They can't just come up with bottles of white liquid, pose before the television cameras and say triumphantly: "We found milk!" It could be paint, or carpenter's glue, or cornstarch and water. Someone has to prove that it is what it seems to be.

Now let's assume the search is negative. The police are sitting in your neighbour's kitchen, asking him to sign some papers. They hear something that sounds distinctly like a moo. They go to the window and sure enough, there's a cow out back.

Oh that, the guy says. Yeah, don't worry -- she doesn't produce. Can't you see there's no grass out there? The poor thing is starving to death.

The problems, broadly speaking, are the same ones faced by weapons inspectors in Iraq. One of them is a classic: How do you prove a negative? How do you prove something doesn't exist, or isn't present?

It's not impossible. But success depends on the boundaries of the question posed.

After simple observation, you can make a categorical statement about whether something is present within a certain three-dimensional space: "I looked inside the fridge, and there was no milk."

But, blur the boundaries, enlarge the space or obscure it, and you're forced into extrapolation, deduction or remote detection: "We couldn't see inside the walls, but the space is too thin to hold anything. Just to be sure, we ran our sensors over them and nothing registered."

Hear the faint whisper of doubt? Now add a fourth dimension -- time -- and you're into the hypothetical: "The cow isn't producing now, but if the grass starts growing you never know. . . ."

Finally, factor in external variables and the possibilities proliferate: "If he got a load of fodder in and bought a couple more cows, he could have a regular dairy running there in six months or so." Now, instead of looking for the presence of a thing, you're trying to prove the existence of a threat.

All right. Back to Iraq, and those inspections.

As the possibility of absolute certainty recedes, so grows the number of pretexts for war. Hard-liners in the Bush administration, who never wanted to bother with weapons inspection in the first place, would seize on anything to prove "material breach" of UN resolutions. Zero tolerance for Saddam, they say. A wax carton in the garbage? Gotcha! Proof of milk!

Alas, life isn't zero tolerance. Over the years, I've written about torture and other atrocities, and worked here and there to promote respect for human rights. But do I advocate all-out, never-ending war against every human-rights abuser? Of course not. Actual harm and imminent risk must be calibrated with strategy, tactics and timing.

Despite their rhetorical displays of cojones, the American hawks aren't in favour of permanent war, either. In and out of power, they not only tolerate but actively aid despots of all kinds -- including Saddam Hussein himself -- when it suits them. We didn't hear them pressing Bill Clinton to move against genocide in Rwanda. We don't hear them advocating war against nuclear North Korea.

Which is why we know that if the United States makes war on Iraq, it will be about a lot more than atrocities, or weapons of mass destruction, or unaccounted-for fingerprints on the fridge door. It will be about diversifying sources of oil, and mostly about giving the United States a giant forward base for advancing its interests in the Arab world.

There's a chance -- just a chance -- that it won't happen. Much depends on the inspections, and on definitions of proof.
pknox@globeandmail.ca