Developing the Mereology of Chemistry

Abstract

The part-whole relation is fundamental to the theory and practice of chemistry. Philosophers have recently began to study this relation as it appears in various contexts resulting in the identification of a variety of ways that rules for mereological reasoning can be developed. We show that it is impossible to abstract a common part-whole structure that is applicable across the whole of chemical science. How parts and wholes are identified and how they are related context by context depend on a variety of contingencies, including locally valid theories, experimental apparatus and techniques, and the hierarchies of environment within which chemical reactions occur and chemical bodies are identified and refined. We illustrate these points with examples from recent chemistry, and display their significance in the molecular orbital thinking of Robert S. Mulliken. Philosophers have come up with two main ways of developing a system of rules for mereological reasoning: rules for reasoning in which the parts and wholes and subsets and sets (David Lewis), and rules for reasoning in which the parts are constituents of the relative wholes (Stanislaw Lesniewski). Both mereologies have a place in chemical thinking.