Modal Logic
Modal logic examines necessity and possibility, and related paired notions such as validity and consistency, obligation and permission, and the known versus the not-ruled-out. Offered by MIT OpenCourseWare, this first course in the area assumes a solid background in first-order logic. Topics include the main systems of propositional modal logic, Kripkean possible-world semantics, strict implication, contingent identity, intensional objects, counterpart theory, the logic of actuality, and deontic and epistemic logic. The emphasis falls on technical methods and formal results rather than philosophical applications. Materials follow MIT's OCW format: lecture notes, readings, and problem sets drawn from the original course, free to access under a Creative Commons license, with no certificate offered. Suited to students who already handle quantifiers and proofs comfortably and want to extend that toolkit to modal systems.