Abstract

Diagrams are hybrid entities, which incorporate both linguistic and pictorial elements, and are crucial to any account of scientific and mathematical reasoning. Hence, they offer a rich source of examples to examine the relation between model-theoretic considerations and linguistic features. Diagrams also play different roles in different fields. In scientific practice, their role tends not to be evidential in nature, and includes: highlighting relevant relations in a micrograph ; sketching the plan for an experiment; and expressing expected visually salient information about the outcome of an experiment. None of these traits are evidential; rather they are all pragmatic. In contrast, in mathematical practice, diagrams are used as heuristic tools in proof construction ; notational devices; and full-blown proof procedures. Some of these traits are evidential. After assessing these different roles, I explain why diagrams are used in the way they are in these two fields. The result leads to an account of different styles of scientific reasoning within a broadly model-based conception.