Monday, January 24, 2011
The most precise and clear way of getting to a real definition is by what is called "genus-species classification". One must not confuse this with something like "biological species" which are these days based off of evolutionary lineage. In terms of giving real definitions of things, it usually has very little to do with that. The easiest way to understand this is with set theory and venn diagrams. In terms of set theory, a genus is just a type of superset and a species is a type of subset. A superset counts as a genus when all of the members of its subsets share certain particular attributes in common. A subset counts as a species when its members all have some special attribute which demarcates them from the members of the other subsets. This difference is called the "specific difference". So with the case of the kitty, the genus is "cat", since kitties have all of the attributes necessary to be included in the genus (superset) of cats. However, a kitty is different from other cats insofar as it is young. So the specific difference is the attribute of its youth. This creates a separate species from other cats, such as adult ones who have the specific difference of mature age. Maybe the venn diagram above is illuminating.
So to get a real definition of kitty we take the species and genus, giving us "young cat". Hypothetically, one could do this with any given natural kind of thing.