 Many have pointed to Peirce’s theory of signs, which classifies signs as being of three kinds—symbols, indices, and icons—as the foremost theoretical background for Peirce’s  EG.[23]  For example, as will be shown below, ovals and lines, along with letters, are the basic vocabulary of Peirce’s EG. It is natural to connect Peirce’s interest in icons with his invention of graphical systems, and the connection is real (Shin 2002: 22–35). However, to pinpoint the features of icons and the iconic nature of Peirce’s graphical systems requires much more work than our intuition provides. Moreover, there is a big gap between Peirce’s discussions of  icons[24]  and his invention of full-blown graphical systems; something else has to be brought into the picture to explain how Peirce got from his initial ideas about icons all the way to his EG.