The fact that such arguments show only that F is an essential property of K means that they are invulnerable to complaints that not everything with F is K. For example it is sometimes complained that water cannot be essentially H2O for the following reasons (a) water is a liquid, whereas a substance comprised of H2O can exist as a solid or a gas; (b) a single H2O molecule is not a sample of water because it does not have the properties we can ascribe to samples of water (such as a temperature);