Because semantics and categorization are key themes in document engineering and in the courses I teach, I've been flabbergasted by much of the recent reaction to the "demotion" of Pluto from planethood to the inferior status of "dwarf planet"” by the International Astronomical Union. The IAU recently passed a resolution that defined a planet within our solar system as:


A celestial body that is (a) in orbit around a star, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.


Because Pluto doesn't satisfy the third requirement, it no longer is classified as a planet. This has generated a great deal of news and caused lots of people to get upset. A typical headline is "Pluto's demotion has schools spinning" -- elementary school science teachers just don't know what to teach. And the widow of the astronomer who discovered Pluto in 1930 says she is all shook up.

But "Pluto's place is safe with astrologers" and that's crucially important to me because apparently Pluto is the most important planet for Scorpios and I am a Scorpio.

These stories are pathetically amusing and that alone makes them interesting, but what really intrigues me is how they illustrate how people understand categories. "Planet" is a category with profound historical and cultural importance, and because of the IAC resolution, we get to witness a very clear and sudden shift in how that category is defined.

For millennia we earthlings have had a notion of planet as a "wandering" celestial object, but because we only knew of planets in our own solar system, we could define "planet" by enumeration. Very few categories can be understood that way, that is, by making an exhaustive list of their members. But once we acknowledge the existence of planets outside our solar system, the set of planets becomes unbounded, and the lack of a definition becomes apparent. Then we can have arguments about the definitions, and hence biases of one kind or another get built into the categorization.

The popular reaction to this new way of understanding "planet" by extensional definition rather than by enumeration suggests that many people are living with the delusion that there is an objective reality in which categories and definitions are objective and unchanging. And it is scary to read that the IAC members gave serious discussion to the likely impact their new definition would have on elementary school science. I thought progress in science, scientific revolutions, creative destruction and all that meant that we should look forward and not worry about the “installed base” of people with a sixth-grade science education.

-Bob Glushko

The other day during the end-of-semester review for my Information Organization and Retrieval course at UC Berkeley I reminded my students that every classification scheme is biased. Even when this message is softened by rephrasing it as every classification takes a point of view it doesn’t sit well with people who want to believe in "reality" where categories are based on objective features or characteristics of objects, documents, or other "bibliographic entities" that we want to describe.

A few months ago when Pluto’s "demotion" from the "planet" category was a hot topic I wrote about how poorly people understand the nature of categories and classification systems. Yesterday I ran across another example, this one involving lobsters, which I’ve also written about in the different contexts of logistics and customs documentation.

This new lobster story has been reported on National Public Radio and in the Economist (2 December 2006 print edition, story titled "Dueling Decapods") and concerns a dispute about what can be called a lobster. The state of Maine wants to protect its lobster industry by enforcing some rules about the lobster category.

Maine's first approach is downright silly, branding lobsters as "Certified Maine Lobsters" in a jingoistic attempt to smear lobsters from Nova Scotia or New Hampshire as somehow inferior. This classification is unscientific because it denies the fact that lobsters migrate. If Maine's goal is to classify lobsters by geographic origin, I think it needs to distinguish native ones from those "just passin' through" from Nova Scotia who are visiting their Maine relatives.

And furthermore, 60-70% of the lobsters caught in Maine are exported to Canada for processing, and many of them are then re-exported to the US. So many "Canadian" lobsters are in fact incorrectly classified as "Maine" ones, except for those that were born in Canada and unfortunately caught as tourists "passin' through" Maine's waters.

A second front in the lobster classification war concerns whether a "langostino" can be marketed as lobster. From the perspective of biological taxonomy, both langostinos and lobsters are "decapods," hence the title of the Economist article, but the former isn't a lobster. So this time, instead of denying science to establish a classification scheme, Maine is relying on it. However, the Wikipedia entry for "langostino" says that:

Langostino is a Spanish word for prawn that is commonly used by restaurants to refer to the meat of the "squat lobster," which is neither a true lobster nor a prawn.

So there are some conflicts between scientific classification and "folk" classification. The US FDA sides with the restaurant industry and recognizes that many people think of langostino as a kind of lobster, and so it approved that classification on restaurant menus. But this unscientific classification has outraged Maine's senator Olympia Stowe, and she has asked the FDA to reconsider:

"Permitting this inferior product to be improperly marketed as 'lobster' not only pollutes consumers' appetite for real lobster, but it also exposes consumers who suffer from certain allergies to potentially life-threatening allergic reactions."


Perhaps Maine needs a branch of the “Minutemen” dedicated to securing its borders against illegal lobsters. But their rules of engagement would be complicated. They would want to let migrating lobsters in but then not let them leave in order to let Maine report higher numbers of "Certified Maine Lobsters." But they would want to stop all langostinos at the border.

-Bob Glushko