Knowledge, language, existence, and mind are the core themes of theoretical philosophy, which are addressed in the disciplines of epistemology, philosophy of language, metaphysics, and philosophy of mind. In four extensive chapters, the author provides a fundamental and illustrative introduction to these disciplines, explains the central questions, concepts, and methods, and discusses relevant positions and arguments. The book is designed in a two-color layout with numerous definitions, examples, argument analyses, and deep dives.