 Peirce, a founder of modern quantified logic, also invented a graphical system, called Existential Graphs, which is logically equivalent to predicate logic. Along with Don Robert’s pioneering work on Existential Graphs and John Sowa’s creative application of Peirce’s graphs, recently a group of diagrammatic researchers provided more diverse approaches to Existential Graphs in a broader theoretical context (Shin  2003).  