This is the first of a three-volume collection of David Lewis' most recent papers in all the areas to which he has made significant contributions. This first volume is devoted to Lewis' work on philosophical logic from the past twenty-five years. The topics covered include: deploying the methods of formal semantics from artificial formalized languages to natural languages, model-theoretic investigations of intensional logic, contradiction, relevance, the differences between analog and digital representation, and questions arising from the construction of ambitious formalized philosophical systems.