Understanding phenomena by building models: Methodological studies on physical chemistry

Abstract

We seek to elucidate the explanatory and exploratory roles of models in physical chemistry. Models are mostly understood as cognitive instruments supposed to account for a restricted range of data. We elaborate general dimensions of model-building in this first section and distinguish between model-building by enriching and reducing a nomological core. We focus on intermediate and idealized models. Intermediate models incorporate basic principles of physics, but their more detailed results are shaped by additional suppositions. Idealization involves the reduction of the nomological core of models. Models can also be used for exploratory purposes. Cognitive models are heuristically useful because they serve to evaluate quantities inaccessible otherwise. In a similar vein, we examine the exploratory use of concrete realizations or analog models in studying problems from surface science. Our general claim is that considering the two dimensions of model-building, that is, enriching and reducing the nomological core, is suited and sufficient to account for the explanatory power and the exploratory fruitfulness of models in physical chemistry. This suitability depends on the possibility of constructing modular or non-holistic models. Such models are distinguished by the context-independent impact of specific assumptions on the model outcome. In holistic models, one and the same assumption may produce quite distinct empirical consequences in different model environments. The features we highlight are supposed to be generalizable to model-building in the physical sciences.