Abstract

Natural kind realists believe that the world is carved out into kinds of things. Critiques addressed towards natural kind realism aimed at showing the difficulties in discerning a universal spatial structure and behavior common to all the members of an alleged kind. Little or no attention, however, has been given to the temporal structure of a natural kind. After showing (in the first section) that some kinds are indeed temporally extended, the second section of the paper argues that there is no non-arbitrary way of tracing the natural temporal structure of a kind. The accrued result poses a novel problem for natural kind theorists, as it clashes with the basic expectancy that if a kind is indeed natural, both its spatial and temporal boundaries should be (at least in principle) discernible.