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There are nine canonical planets. The problem begins because one of them, Pluto, is really not up to the measure of the others. It is just an icy rock ball on the periphery of the solar system, but common usage and popular opinion holds that it is a planet. Worse still, there are comparably sized rocks out there; for example, 2003 UB313 aka Xena. Whatever the scientific merits of the case, the guys down at the Dairy Queen won't stand for Pluto being demoted from planet to mere rock. As Janet explains, "Pluto is too a planet! It was a planet when I learned it in school, and it hasn't gotten any smaller since then!" This is a nice example of the way that scientific concerns and common usage together shape how we decide to use words.
The proposed definition is this:
A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.
This is not oddly disjunctive; neither does it merely stipulate a list of members. So it surely picks out a natural kind.[1]
This definition includes all nine canonical planets. The trick is that it would include many objects not currently considered planets. Xena, for example. Also Charon, which is typically considered a moon of Pluto.
Ceres, the largest asteroid, would also be a planet. This militates against common usage-- the guy at the Dairy Queen knows that asteroids ain't planets-- but Ceres was classified as a planet when it was first discovered in 1801. Asteroids were, in the early days, called 'planetoids' and 'minor planets.' Moreover, Ceres is not just some Oldsmobile-sized chunk of rock. It is 930 km across and comprises about a quarter of the asteroid belt's total mass.
So: The definition is principled, preserves Pluto's planethood, and satisfies the desideratum that every planet we learned about in school should count as a planet. All the same, I think the definition is tantamount to kicking Pluto out of the planet club.
As a rough approximation, people will remember lists of seven items, plus or minus two. Nine planets, fine planets-- yes. But twelve planets, three too many. Once lists get too long, people cluster the items. Instead of having more items, there is one list of kinds of items and seperate lists for each kind.
This is already happening. The eight planets from Mercury to Uranus are classical planets. Ceres is a dwarf planet. Pluto, Charon, and Xena are plutonic planets; dropping the 'planet' moniker entirely, these are plutons. The club of eight retains its aristocratic standards.
I predict that, if the proposal is accepted, then in two decades 'classical' will be dropped in ordinary conversation. Dwarf planets and plutons will have to be specified as such.
[1] As readers will recall, I am inclined to be ecumenical about natural kinds. I might count a stipulated list of the canonical nine planets as a natural kind. That does not mean that we should use the word 'planet' to pick out just those nine things, however.
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I completed my dissertation after digital technology had overtaken document preparation, but before it overtook the submission and archiving of dissertations. I prepared it in LaTeX, processed it as a PDF, printed it on cotton paper, and submitted it in duplicate to the Office of Graduate Studies and Research. OGSR sent both copies to the library, and one copy was forwarded to University Microfilms, Inc. UMI photographed the pages so as to make a copy on microfilm, scanned the microfilm, and made the scans available as a PDF. It is a grainy, uneven scan. It is not searchable. UMI charges money for it, unless you request it from the UCSD network.
It is the 21st century, and we can do better. I have made the original PDF available via Lulu. The fonts are fonts, and they render as vectors. The contents are fully searchable. It is available free, even if you do not live in La Jolla. I opted for Lulu because it provides a kind of backup, and also because they will print hardcopies on demand for anyone who might care. The thought of someone using up an inkjet cartridge to print it is too much to bear.
I should say, in all honesty, that it probably isn't worth your time to look. I am really only doing this because I can.
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To sum up last weekend: The Computing and Philosophy conference had suitable proportions of computing, philosophy, food, wine, and camaraderie. Kudos to the organizers for running a tight ship.
I promoted forall x at every reasonable opportunity. I put out fliers and a sample copy in the book exhibit; someone thought enough of it to walk off with the sample copy at the end of the conference, which is a kind of compliment. I had several conversations about it, some with people who are actively trying to pick a logic textbook.
The presentation of my Wikipedia paper went well. In addition to the discussion immediately after the talk, I had some excellent chats later in the weekend. You can watch the video of my talk online, if you are so inclined. (It's in Windows Media format, and I take up about the first third of the stream.) Watching it makes me cringe at how often I interpose 'um' between otherwise interesting words.
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I've filled the lacuna in Epistemology and Wikipedia. The conference starts tomorrow, and I present Friday.
I've also posted the updated version of Tom Reid meets Tom Bayes, which continues its quixotic quest to collect rejection notices from the finest philosophy journals.
Eliminating Induction, ditto.
As always, feedback on the papers is welcome. Anything from 'Hmm' to 'Terrible fallacy on page eight' can either be sent by e-mail or commented here in the blog.
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I have a draft of Epistemology and Wikipedia on-line. The paper has existed as detailed notes for quite some time, but I finally hammered it out as paragraphs. It is still waiting on some data, so there is a lacuna in the present draft. I will be presenting it at the Computing and Philosophy Conference next week, and hopefully the lacuna can be filled by then.
The paper concludes with the claim that Wikipedia "frustrates the methods by which we judge the claims of traditional information sources like encyclopedias. This does not mean that Wikipedia is worthless or that we ought not use it at all. Yet it does mean that we should be wary of it and that we should try to develop methods which are suitable to it."
In an earlier draft, I surveyed some cautious ways in which we might use the Wikipedia:
1. Wikipedia entries often contain links to related pages around the web. I know people who exploit this feature and visit the Wikipedia when looking for relevant links. It lets them get at a page quickly, without trying to coax the relevant URL from a search engine. This is fine, but it does not involve actually trusting a claim made in Wikipedia itself.
2. I use Wikipedia to keep track of comic book plots, since I no longer actively read comic books but have friends that do. For topics that have a dedicated fan base, the Wikipedia articles are well tended.
3. It is tempting to say that we can rely on Wikipedia when looking up trivia: Although the Wikipedia might mislead us, the cost of being misled about trivia would be low. This seems wrong to me.
Suppose I consult Wikipedia on some matter that does not seem important, and I come to believe whatever Wikipedia has to say. At a later date, when the topic is more important, I remember what I read without remembering where I read it. There is debate among epistemologists about whether detaching a belief in this way is ever responsible, but it is certainly something that happens. It is a danger of consulting Wikipedia. I wish I could quantify this danger, but I do not know enough about the psychology of belief to say anything more precise.
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