Sharif Digital Repository

In this thesis, different systems of quantified modal logic, philosophical theories of possibilism and actualism, and the interaction between these two theories and those systems have been studied.Modal claims, which talk about the world as it could have been and not the world as it is, have by far been under philosophical considerations. Possibilism and actualism, two philosophical theses that have their own point of view towards the world and its objects, analyze these claims and their relevant truth-assigning mechanisms in different ways.On the other hand, over the last century, modal sentences have been formulated, in sentencial and quantified levels, by precise logical systems, called...