Me and Bob are going to add some tomatoes and other vegetables to the pasta.
You know tomato is actually a fruit. And I think you mean 'Bob and I.'
Oh, then you must not have meant to start a sentence with a conjunction just now...
anyway. we can tell that the tomato IS a vegetable because that fact organizes things physically in the world. for example:
1. the produce aisle.
2. the garden patch.
3. the hamburger. ask a friend: "have you ever tried fruit on your hamburger? it's actually great..."
4. it tastes like a vegetable, whatever that means.
and so on.
that is, the 'technical' definitions of a fruit ('the sweet and fleshy product of a tree or other plant that contains seed and can be eaten as food') and a vegetable ('edible part of a plant cultivated for food', thank you dictionary.com) are useful in some speech communities: scientific, botanical; but are incomplete and unable to explain certain facts about the physical tomato (it goes in the vegetable section of the supermarket). nevermind for the moment that 'vegetable' seems to include 'fruit' under these definitions. i'm fairly sure that in most speech settings they're a binary. enough to make the point, at least.
Scott gets credit for the observation that 'fruit' is by far the privileged side of the 'fruit'/'vegetable' binary. consider calling a person a 'fruit;' this is either a derrogative term for a homosexual man (but not nearly as offensive as some other words) or just a goofy person. calling someone a 'vegetable,' on the other hand, is an offensive way of saying that they are literally comatose or brain-dead, or a very offensive way of saying that they are a 'couch potato.' consider the brave tomato, following its instincts in spite of confusion from humans and jeers from the other fruits.
the Essentialist school of philosophy (and philosophy of language), which claims that any specific type of entity can be defined as a class such that every member of that class must share some finite list of characteristics (thank you wikipedia), would have a hard time with the tomato. poor confused tomato. it seems trivial, but figures like the tomato, which straddle two or more categories, have major implications in certain fields: the weeks-old fetus - human or not? the transgendered person - male or female? meaning - inside or outside of language? the answers to these questions are essentially decided by the usage of the terms, which can never be completely controlled by dictionaries, laws or experimentation.
calling 'a tomato is a vegetable' a category error means several things. it means you rely on a certain scientific and physical definition to determine the 'actual' 'real' 'true' category of an object. it also means you believe much of the world is often making errors by not adhering to that standard definition. it might also mean you think that everything definitively fits in one category or the other, and that this category can be determined (a transsexual IS actually male or female, a fetus actually begins living at a particular instant) as long as you have enough physical evidence.
and, while that isn't necessarily bad, it does, like the questioning tomato, make me slightly uncomfortable.