A possible world is a way things might be or have been, in some respects similar to the real world, in some others, different.
Possible worlds semantics raises many philosophical questions, from the metaphysical status of worlds (Do possible worlds different from actuality really exist? If so, what are these things?), to the meaningfulness of quantification over nonactual individuals. This course introduces both to the logical techniques of, and to the philosophical issues raised by, firstorder modal logic, which combines the language of first order-logic with quantifiers, identity, names and descriptions, with modal operators. We will explore such topics as: The metaphysics of possible worlds, possibilia, and fictional objects; The behaviour of identity in modal contexts; The differences between constant and variable domain semantics, actualist and possibilist quantification; The Barcan formulas; Lambda-abstraction; Rigid and non-rigid designation; Empty terms; Formal accounts of descriptions. We will also look at the burgeoning topic of non-normal worlds: worlds where logical laws may fail. These anarchic worlds have proved useful to model phenomena of great interest for philosophers and logicians, from doxastic logics for non-logically-omniscient agents, to counterpossible conditionals, to hyperintensional phenomena. They also allow a smooth semantic treatment of non-classical alternatives to mainstream logic, such as non-normal modal logics and relevant logics.
Students will be evaluated based on a final written exam.