Sun-Joo Shin. The Logical Status of Diagrams. Cambridge/New York, Cambridge University Press, 1995.

Bishop's UniversityLennoxville, QuebecCanada, JIM 1Z72nd grade teacher: Genny, you must try not to use your fingers when youcount.9th grade teacher: Genny, remember the triangle you drew is just a crudepicture of a real triangle. Real triangles can't actually be seen. Geometry isin the mind — not the eyes!College logic instructor: Now, keep in mind, Genny, that these Venndiagrams are nothing more than heuristic devices, visual aids to theunderstanding. When you have mastered the techniques of formal inferenceyou can dispense with diagrammatic crutches.Friend: Genny, I can't believe you're still wearing that old watch; analogueis, like, so passe.Supervior, engineering firm: Genny, work up a flow chart for the newcomputer programme and attach a wiring diagram for the next console line.When you finish, drive over to Mr. Peirce's office for our meeting. Usethis map to get there.In spite of the fact that charts, maps, family trees, and diagrams of allsort are a common part of our daily lives, mathematicians and logicianshave generally denigrated the use of visual devices. Genuine formalreasoning, so the claim goes, takes place in the head. Pictures may help thenovice to get the right idea, but they are really incidental to the process.Most particularly, they say, such devices could never serve as a medium forreasoning per se. A diagram is never to be taken as a proof.This general prejudice against diagrammatic methods of proof is fairlyrecent (at least among mathematical logicians). There is good textualevidence that Aristotle made use of some form of diagrams in his originalaccount of syllogistic, as witness his use of (Greek equivalents of) such