title: Axioms for branching time
abstract: Logics of general branching time, or historical necessity, have long been studied but important axiomatization questions remain open. Here the difficulties of finding axioms for such logics are considered and ideas for solving some of the main open problems are presented. A new, more expressive logical account is also given to support Peirce's prohibition on truth values being attached to the contingent future
keyphrases: axioms branching time truth values temporal logic