 In addition to these sorts of claims about the essential properties of ordinary individuals, claims about the essential properties of natural kinds have figured prominently in the literature, since Kripke (1972/1980) and Putnam (1975) made essentialist claims concerning, for example, cats and water. The core intuitions are that in any possible world anything that is not an animal is not a cat and that in any possible world anything that is not composed of molecules of H2O is not water. Since we discovered empirically that cats are animals (and not, for example, robots) and that water is H2O (and not some other type of molecule), each of these claims asserts a necessary a posteriori connection between two properties. In the first case, what is asserted is that it is necessary that anything that is a cat is an animal. In the second case, what is asserted is that necessarily anything that is (a sample of) water is composed of molecules of  H2O.[6]  It is natural to construe these claims on the model of the essentialist claims we have so far considered: it is essential to a particular object, namely the species cat, to be such that all of its instances are also instances of the kind animal; it is essential to a particular object, namely the kind water, to be such that all samples of it are composed of molecules of H2O. Notice that one may hold that cats are essentially animals in the sense that there is a necessary a posteriori connection between the property of being a cat and the property of being an animal, without holding that any particular cat is essentially an animal. In other words, from the fact that it is necessary that every individual that is a cat is an animal, it does not follow that every individual that is in fact a cat is such that necessarily it is an animal. In still other words, this type of essentialism about natural kinds does not entail sortal essentialism.