IIT Kanpur. Modal logic extends classical logic with the ability to express not only 'P is true', but also statements like 'P is known' or 'P is necessarily true'. We will define several varieties of normal modal logic systems (K, T, D,S4, S5), providing both their semantics and their axiomatic proof systems, and prove their standard soundness and completeness theorems. On completion of the course, students are expected to have a good understanding of the technical details of the logic covered, and use it under various contexts including some of philosophical debates surrounding these logics. (from nptel.ac.in)