Wittgenstein, Aristotle and Pluto

Wittgenstein, Aristotle and Pluto

By BRIAN M. CARNEY
September 2, 2006;
The Wall Street Journal
Editorial

If Aristotle had known about the planet Pluto, recently sent into ignominious exile, he probably would have called it Hades, the Greek name for the god of the underworld. But would the philosopher have called the celestial object a planet? Plato's greatest student did not do his best work in astronomy. But his "Nichomachean Ethics" offers some guidance for those who question the decision to demote Pluto to "dwarf" status.

Early in the "Ethics," Aristotle cautions his readers that every field of study should aim for a degree of precision appropriate to the subject matter. "The same exactness must not be expected in all departments of philosophy alike," Aristotle wrote, "any more than in all the products of the arts and crafts." The officious astronomers who redefined planethood to exclude Pluto are guilty of what scholars of Aristotle like to call a "category mistake." They are striving for a degree of precision inappropriate to their subject matter.

More than 2,000 years after Aristotle, another philosopher, Ludwig Wittgenstein, made a related point about definitions. Wittgenstein asked his readers to come up with a definition for the word "game." He then proceeded to show that this was not a trivial task. Some games involve competition, but not all do. Some have fixed rules or a defined end-point, but some do not. Most games are fun, somehow defined. But the differences between ring-around-the-rosie and chess are much easier to discern than their similarities. Wittgenstein's point was not that we don't know what a game is, but rather that we are perfectly capable of using the word and understanding it without possessing a mental rule that includes every activity we might call a game and excludes everything that is clearly not a game.

The recent campaign against Pluto's planethood proceeds from the assumption that we can't really know what we're talking about when it comes to planets unless we have a "strict" definition. Without a rule, the argument runs, we don't really know what a planet is at all. Does this make any sense?

That depends on the stakes. If we ask, "Who is a citizen of the United States?" it is important that we have a definition and a set of rules for answering the question unambiguously in any conceivable present or future case. Voting rights, entitlement eligibility and the obligation to pay taxes on one's world-wide income are just three significant areas in which this question matters a great deal. Membership in Club America has its privileges -- and downsides.

Things are different at Club Planet, though. Pluto receives no subsidies, pays no dues and has no privileges by virtue of being admitted or excluded from the club. It gets to keep its off-kilter orbit and its distance from the sun whether it is a planet or merely a "dwarf." Neptune can't cut off the cute little shortcut Pluto takes across its neighbor's orbit every 250 years or so, no matter what names astronomers or the bigger planets call it. Nothing turns on whether Pluto is a "dwarf" or not.

Which brings us full circle. Defining planethood is an exercise in ersatz precision. At the end of the day, it's a judgment call. What's more, the recently drawn boundaries of Club Planet were not developed in a vacuum. They were designed to achieve a preordained result.

If some faction wanted Pluto out of the club, it could have just kicked him out. Instead they drew up a rule and then declared, "Lookee here at the rule book! Sorry, Pluto, you'll have to go. Not our fault, you understand -- rules is rules."

But defining "planet" is not a moonshot. And until last month, most of us thought that Pluto was a planet. Where was the harm in that?

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