Topics Language

Question Why is it so easy to define "island" and so difficult to define "dog"? Both terms refer to quite "natural" and well-known things. We can say that an island is an area of land surrounded by water, but we can't say, for instance, that a dog is an animal that barks, since a sick dog that can't bark is still a dog. It is also curious that we all know what a dog is without knowing the zoological definition of this species. Is there a name for this difference between the two words?

Accepted:
December 9, 2006

Comments

I'm a little bit worried about Australia, but let's leave that continent to one side. Sometimes what makes something a particular kind of thing is a set of superficial properties, while in other cases the relevant properties are less obvious. Island is in the former group, dog is the in the latter. Presumably what makes something a dog has something to do with its genetic makeup, not superficial properties like its bark. In a way, this is surprising, since we talked about dogs before we know anything about genes, and even today I talk confidently about dogs without knowing how they differ genetically from cats. But Saul Kripke and Hilary Putnam have given plausible accounts of how this is possible. Imagine someone who wanted to introduce a name for a biogical kind nobody had named before. It might be someone who sees member of an exotic new species of animal. She could point to some members of that species and say something like, 'let's call that animal and every other animal of the same species a "snorgle"'. What makes all those animals snorgles is their shared genotype, but the naming of the kind didn't depend on namer knowing this. And this also explains why it would be so difficult for this person to give any very informative definition of a snorgle, even though she now has no difficulty referring to the kind.