THE METAPHYSICS OF NATURAL KINDS Synthese 2015 online first http://link.springer.com/article/10.1007/s11229-015-0833-y Alexander Bird University of Bristol Abstract This paper maps the landscape for a range of views concerning the meta- physics of natural kinds. I consider a range of increasingly ontologically committed views concerning natural kinds and the possible arguments for them. I then ask how these relate to natural kind essentialism, arguing that essentialism requires commitment to kinds as entities. I conclude by examining the homeostatic property cluster view of kinds in the light of the general understanding of kinds developed. 1 Introduction The principal aim of this paper is to examine the various options concerning the metaphysics of natural kinds, in particular as regards their ontology. Ini- tially I proceed by posing a series of questions whose positive answers corre- spond to a sequence of increasingly metaphysically committed views about natural kinds. In section 2 these questions concern the naturalness and kind- hood of natural kinds. This leads, in section 3 to the question whether natural kinds are themselves genuine entities. In section 4 I present an argument for a positive answer to the existence question, that takes essentialism about natural kinds to imply their existence: (having an) essence implies existence. In section 5 I consider the objection that kind essentialism reduces to individual essential- ism, which would undermine the import of the essence-implies-existence ar- gument. In sections 6 and 7, I put this machinery to work, asking first what sort 1