Ruth Barcan Marcus is famous for her influential work in modal logic.
Her perhaps most distinctive contribution to the subject, the so-called
Barcan formula, states that if it is possible that something has a certain
property, then there is something that possibly has that property.
The Barcan formula gave rise to an extensive debate concerning the interpretation
of systems of modal logic. In recent years, Marcus has been writing on issues
concerning belief and rationality rejecting received accounts of propositional
attitudes and attempts to systematize epistemic logic. This talk discusses this
lesser known part of Marcusís contribution to philosophy and logic.