(the pdf version of this entry)
It is strange to start this blog with a text on modal logic. Historically, the language of model theory has been the language of first-order logic (although recently there are efforts to go beyond first-order context), and this choice turned out to be so good that all the other logics that use other languages has become known under the name of “non-classical logics”. Among those non-classical logics modal logics is probably the simplest and the most general class of logics.
Indeed, the least that you expect from a logic is to be able to express boolean connectives: “and”, “or”, “not” and such. Modal logics add very little to those: they add one or several so-called modalities, (more…)
