ABSTRACT
In the 1970s, Saul kripke and Hilary Putnam developed a causal theory of the reference of natural-kind terms, central to which were two chemical examples: water and gold. kripke and Putnam assumed that chemical-kind terms tracked microstructural properties, the extensions of element names being determined by sameness of nuclear charge (gold is the element with atomic number 79); and those of compound substances determined by their chemical structure (water is H2O). Central to this view is semantic externalism, the thesis that the extension of a kind term can be determined by properties of which users of the term may be ignorant. Thus “gold” referred to stuff with atomic number 79 long before atomic number was thought of, and the twentieth-century identification of gold as the element with atomic number 79 constituted an empirical discovery, rather than a refinement or revision of its definition. This is not the place to rehearse kripke’s and Putnam’s arguments for their view. Instead I will concentrate on the claim that the extensions of the names of chemical substances are determined by microstructural properties, beginning with a survey of different chemical kinds.
