Abstract: Presentations of geometric proofs are often accompanied by diagrams for quick and easy comprehension. But to many people, it seems clear that diagrammatic reasoning cannot be a part of the argument itself, otherwise it would be prey to the very insecurity that we want to eliminate — insecurity from visual thinking — and so the argument would not be able to justify its conclusion; it would not be a proof. This is the line of thought that most strongly supports the widespread belief that diagrams can have no epistemological role in proof. The main aim of this chapter is to investigate this negative view and the argument for it presented in this book.

Keywords: geometric proofs, diagrams, geometry, discovery, insecurity, visual thinking,