Peirce’s graphs amended

Abstract

One of the claims made for C. S. Peirce's existential graphs has been that they are a deductively complete formulation of first-order logic with identity. As Peirce presented them, this is true only for certain versions of first-order logic :those which do not include terms for individuals. I amend Peirce's rules here, showing, in particular, how they are capable of demonstrating that, for instance, ‘Jack is in the kitchen’ contradicts ‘Jack is not in the kitchen’