FROM THE NEW YORK TIMES:

SADDAM’S SWAN SONG

Iraq Makes a Philosophically Flawed Effort to Disprove a Negative

By EMILY EAKIN

How many pages does it take to prove a negative? Iraq is hoping 12,000 might do the trick. That, roughly,
is the number of pages in the declaration it turned over to the United Nations in a last-ditch effort to convince the world that it has no weapons of mass destruction. For the moment, the United Nations and the United States are playing along, scouring the document page by page last week for signs that Iraq is lying or fudging the truth.

    But while the exercise may make for good politics, as a philosophical proposition
it is arguably deeply flawed. In fact, some scholars would say the task
the world has assigned Iraq ˜ to prove it has no weapons of mass destruction
˜ is logically impossible.

    The problem
is not, as is frequently assumed, that proving a negative simply can’t
be done.

    “If I
say I have no coins in my pocket, you can just search me,” said Colin McGinn,
a professor of philosophy at Rutgers University, pointing out that people
verify modest negative statements all the time with little difficulty.

    But philosophically
speaking, there’s a big difference between claiming there are no coins
in your pocket and claiming there are no coins in the pockets of New Yorkers,
or, more to the point, no weapons of mass destruction anywhere in the nearly
170,000 square miles that make up the state of Iraq.

    As the
scope of the claim grows, so do the number of philosophical objections
and practical obstacles to proving it. This is where the work of the 18th-century
Scottish philosopher David Hume comes in. In a dazzling insight that changed
the course of Western philosophy, Hume demonstrated that the common practice
of induction (inferring general rules from particular observations) is
inherently circular and unreliable.

    Philosophers
like to explain Hume’s argument using swans. Ronald J. Allen, a law professor
and evidence expert at Northwestern University, put it this way: “Suppose
somebody claims all the swans are white. He says, `I’ll prove it to you.’
He takes you to the zoo, and there are 20 swans there, all white. Well,
he’s merely showing you a finite set of swans. This can’t establish that
all swans are white.”

    Because
no one can ever observe all the swans in the world, but only particular
groups of swans, according to Hume it would be logically indefensible to
conclude that all swans are white no matter how reasonable such an inference
seems.

    This
same difficulty arises in trying to prove some large-scope negatives, Mr.
Allen points out. “Suppose you assert that there are no black swans,” he
said. “You’d have to produce all the swans in the world to show there are
no black ones” ˜ an impossible undertaking.

    This,
he said, is the situation faced by Iraq. “You can see the perversity of
it,” Mr. Allen said. “The Iraqis have to show that there’s no state of
the universe inconsistent with the statement that they have no weapons
of mass destruction.”

IF Mr. Allen is right, weapons
inspections that turn up nothing, and a 12,000-page declaration that discloses
no violations, are of extremely limited value. Like groups of white swans,
they might tell us something particular but nothing general. They certainly
don’t prove anything about Iraq’s claim that it possesses no weapons of
mass destruction.

    Of course,
it is possible to argue that Iraq’s situation more closely resembles Mr.
McGinn’s single pocket example (a small-scope, easily verified negative)
than it does Mr. Allen’s black swan example (a large-scope, unverifiable
negative).

    “Iraq
is big, but not that big,” said Simon Blackburn, a professor of philosophy
at Cambridge University and a leading authority on Hume. “There is no more
difficulty to prove there are no weapons of mass destruction than to prove
there’s no rhinoceros in my sitting room.”

    But other
scholars concede that the burden of proof placed on Iraq by the United
Nations is so great that no amount of evidence is likely to suffice. The
Bush administration has often spoken of Iraq’s intention to acquire weapons
of mass destruction, said Brian Leiter, a professor of law and philosophy
at the University of Texas at Austin. Once intention becomes a factor,
he said, Iraq’s situation begins to look more and more like the black swan
problem ˜ an unverifiable negative.

    “I’m
willing to venture it’s impossible for anyone to prove they don’t have
the intention to do something,” he said, adding that placing such a burden
on an American criminal defendant ˜ who, unlike Iraq, is guaranteed a presumption
of innocence ˜ would be unthinkable.

    If Iraq’s
task is demonstrably impossible, on what basis can it be justified? Ultimately,
the best defense may hinge not on logic or law but on more nebulous concepts
like experience and common sense.

    “The
thing we’re asking them to prove, whether you put it positively or negatively,
is so extremely hard to prove that we’re almost rigging the outcome by
the way we put the question,” said Laurence H. Tribe, the Harvard professor
of constitutional law. “But it doesn’t follow that we’re acting in a way
that’s contrary to all our conventional jurisprudential principles.”

CITING Iraq’s past use of
weapons of mass destruction and long record of duplicity on the issue,
Mr. Tribe argued that “we’re acting in a preventative mode where we’re
not prepared as an international community to take the risk that potential
mass destruction will go uncontrolled.”

    That’s
a statement that Hume might have found perfectly reasonable. A practical
man, he realized that in the absence of certain knowledge, experience and
common sense are often the best guides to judgment. The danger arises when
fallible human judgments are confused with truth.

    In the
end, Hume argued, the inevitable uncertainty of knowledge requires, in
response, a rigorous policy of “mitigated skepticism” ˜ the constant application
of “a degree of doubt, and caution, and modesty, which, in all kinds of
scrutiny and decision, ought for ever to accompany a just reasoner.”