Different chemical species are often cited as paradigm examples of structurally delimited natural kinds. While classificatory monism may thus seem plausible for simple molecules, it looks less attractive for complex biological macromolecules. I focus on the case of proteins that are most plausibly individuated by their functions. Is there a single, objective count of proteins? I argue that the vagaries of function individuation infect protein classification. We should be pluralists about macromolecular classification.

I argue for accepting a pluralist approach to species, while rejecting the realism about species espoused by P. Kitcher and a number of other philosophers of biology. I develop an alternative view of species concepts as divisions of organisms into groups for study which are relative to the systematic explanatory interests of biologists at a particular time. I also show how this conception resolves a number of difficult puzzles which plague the application of particular species concepts.

This paper evaluates a general argument for the conclusion that visual representations in science must play the role of truth bearers if they are to figure as legitimate contributors to scientific arguments and explanations. The argument is found to be unsound. An alternative approach to assessing the role of visual representations in science is exemplified by an examination of the role of structural formulas in organic chemistry. Structural formulas are found not to play the role of truth bearers; nonetheless, they (...) contribute to the arguments and explanations of organic chemistry. An early success of conformational analysis is presented in order to illustrate the role of structural formulas in the discourse of organic chemistry. *Received January 2007; revised July 2009. †To contact the author, please write to: Department of Philosophy and Religious Studies, Rowan University, 201 Mullica Hill Road, Glassboro, NJ 08028; e‐mail: [email protected]. (shrink)

Organic chemistry provides fertile ground for scholars interested in understanding the role of non-linguistic representations in scientific thinking. In this discipline, it is not plausible to regard diagrams as simply heuristic aids for expressing or applying what is essentially a linguistic theory. Instead, it is more plausible to think of linguistic representation as supplementing theories whose principal expression is diagrammatic. Among the many sorts of diagrams employed by organic chemists, structural formulas are the most important. In this paper, by examining (...) two central episodes in the development of structural formulas—Kekulé’s proposal of a structure for benzene and Ingold’s explanation of dipole moments in terms of ‘mesomerism’—I investigate how the norms for the production and interpretation of structural formulas evolve in response to experimental results and theoretical developments. I conclude that one principal way in which structural formulas embody the theory of organic chemistry is through these evolving norms. (shrink)

Microstructuralism in the philosophy of chemistry is the thesis that chemical kinds can be individuated in terms of their microstructural properties (Hendry in Philos Sci 73:864–875, 2006 ). Elements provide paradigmatic examples, since the atomic number should suffice to individuate the kind. In theory, Microstructuralism should also characterise higher-level chemical kinds such as molecules, compounds, and macromolecules based on their constituent atomic properties. In this paper, several microstructural theses are distinguished. An analysis of macromolecules such as moonlighting proteins suggests that (...) all the forms of microstructuralism cannot accommodate them. (shrink)