Two Dogmas of Diagrammatic Reasoning: A View from Existential Graphs

In Peirce studies and beyond, including contemporary philosophy of logic and mathematics, there have been two dominant ideas in the mainstream and recent research on diagrammatic reasoning and representation. The first is that diagrams, especially logical diagrams, are visual in senses in which symbolic notations are not. The second idea is that logical diagrams are iconic in senses in which symbolic notations are not. In this paper we submit both of these claims under critical scrutiny. We use Peirce’s system of Existential Graphs, which is the mainstay of diagrammatic reasoning in both historical and systematical senses, as the testing ground. We show that neither of these claims is free from difficulties.