QUOTE:
It's like a venn diagram innit. Things can have similar properties but not be part of the same set

I'm really no mathematician, but I can't visualise that. Two sets (planet and plutoid) with two points of intersection.

Elements: zebra,tiger
Properties: legs? stripes? hair? females nurse offspring with milk? hooves?
Sets: felidae, ungulata

Sorry, you'll have to draw it for me (the Venn diagram to represent planets and plutoids).

However, I'm tempated to go along with a real astronomer (Phil Plait from badastronomy.com) on this subject. On the IAU decision:

QUOTE:
Ignoring for the moment, once again, that it's silly to try to scientifically define a class of objects that are really only defined culturally, these definitions are still unsatisfying to me. A planet-sized object between stars is not a planet? How round is round? How do you define its "neighborhood"? These are still the same objections I made before in my earlier post about this.

Let me once again reiterate that trying to define what a planet is is very, very silly. The very fact that all this [the IAU resolution] is so bizarrely confusing is good evidence of this.

Now I'm really confused. You offer a definition of a planet, and now you're telling us you agree with a guy who says it's silly to define a planet.

As I say, I can see merit in Plait's view that "planet" is inevitably a fairly loose category*, and I can see merit in the IAU view that it would be better as a category with crisper boundaries. What I can't see the merit of is a crispish-boundary definition, like yours, that's got no scientific merit and is completely out of whack with the loose, conventional sense of the word.

(*Mind you, in suggesting that "scientific" and "cultural" definitions are wholly separate things, Plait's being deeply daft.)

I think we also need to separate out the questions of whether the IAU's definition is appropriate and whether any definition is.

I know my definition of a planet has no scientific merit. That's exactly the reason I suggested it.

Stumpy Pepys wrote:

QUOTE:
I know my definition of a planet has no scientific merit. That's exactly the reason I suggested it.

1. But it doesn't work "culturally" either.
2. Should we be defining "planet" or not?

1. Fine, but it was only a suggestion. Rogin's suggestion was equally valid
2. No

Stumpy Pepys wrote:

QUOTE:

2. No

Then why---ah, leave it.

Okay then, one last time.

Any definition of a planet has no scientific merit. However, I'm not advocating banning the word or taking it out of the dictionary, but any definition should be based on a cultural not a scientific definition.

Compare to the definition of 'continent' from dictionary.com, which has also no merit for geographers and geologists.

"One of the main landmasses of the globe, usually reckoned as seven in number."

Are you really suggesting there's no point in scientists categorising objects in space? Everything becomes a generic space-object?

No, but any classification must be empirical.