Structural explanation in chemistry and its evolving forms

Historically, there has been a close relationship between the concepts of structure and of shape. Is the relationship a matter of fact or is it conceptual? Exploring this question with examples enables us to distinguish several senses of structure. Clearly, spatial shape is not conceptually related to constitutive structure, since a molecule may consist only of an ordered set of potentialities. The concept of structure in chemistry developed in the nineteenth century from an ambiguous but essentially taxonomic use in type theory to a realist hypothesis as to the spatial distribution of atoms in the molecule. This development required a defense of the Daltonian view of elements as constituted by minute corpuscularian atoms. Once a realist concept of structure had been established, the issue of the nature of structural explanation could then be addressed. Template explanation formats as well as jigsaw formats can be found in chemistry. The problem of halting a regress of structural explanations leads to a sketch of a way in which physics can serve as a heterogeneous foundation for chemistry without reductionist implications.