 Pace Hacking, Khalidi (2010) argues that in fact the contrast between natural and social kinds is not so stark: even many chemical kinds would not have been instantiated in the world were it not for the fact that a scientist conceived of them and acted on that conception. So in both cases the existence of a classification scheme can cause changes to the extension of the kinds in question. The difference between natural kinds and social kinds is a difference of the degree of control we have over the object of classification. In the chemical domain, for example, the nature of the phenomena themselves imposes greater restrictions on the kinds that we can create. (See also Cooper 2004.)