Thursday, 19 October 2007
Intensional Truth Functions
Dale Jacquette, Penn State University
12:05 pm, 817R Cathedral of Learning

Abstract: The extensionality thesis for truth functions holds that all (weak version) or all and only (strong) truth functions are extensional. If the extensionality thesis is true, then there can be no intensional truth functions. Unfortunately for extensionalism, there is a large family of intensional truth functions that have not been properly recognized in philosophical logic. It is possible to provide truth table definitions of sententially dedicated constant truth functions that fail to satisfy the uniform intersubstitutability of truth functionally equivalent sentences salva veritate criterion of extensionality, and that are consequently intensional. Intensional truth functions constitute counterexamples to the extensionality thesis and raise difficulties for efforts to provide formal criteria of truth functionality and non-truth-functionality.