Existential Graph - The Graphs

The Graphs

Peirce proposed three systems of existential graphs:

• alpha, isomorphic to sentential logic and the two-element Boolean algebra;
• beta, isomorphic to first-order logic with identity, with all formulas closed;
• gamma, (nearly) isomorphic to normal modal logic.

Alpha nests in beta and gamma. Beta does not nest in gamma, quantified modal logic being more than even Peirce could envisage.