Lecture, four hours. Requisites: courses 31, 132. Highly recommended: course 136. Second course in two-term sequence (also see course 136). Metaphysical foundations of modal logic and philosophical basis of model theory of modal logic. What are possible worlds? What is accessibility relation? Is modal logic one logic or one theory? Is its focus logical or metaphysical necessity? Are both notions really distinct? How metaphysically involved is (quantified) modal logic? What is its connection to doctrines of (1) Haecceitism and (2) Aristotelian Essentialism? P/NP or letter grading.