Abstract

The differences between classes and individuals are profound and the fact that biological species are individuals rather than classes provides the basis for organizing knowledge on a causal basis. The class of species is a natural kind and there are laws of nature for this and other classes of natural kinds such as the organism and the molecule. Particular species, like other individuals, function in historical narratives by virtue of laws of nature applying to them. The notion that species can evolve by changing their members is a category mistake. Darwin believed that there is no “essential” difference between species and subspecies in the sense that there is only a quantitative difference between them. The concept of biological species is defined on the basis of a qualitative difference. The rank of taxa can be used to distinguish between important natural kinds. Without such kinds language would become purely referential, and have no “sense” as Frege had put it.