This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book aims to explain why its semantics should be of interest to modern logicians. It argues that the Logic fashions a notion of intentional content from the medieval concept of objective being that is consistent with Rene Descartes substance-mode ontology and avoids assigning to objective being a special ontological status. The book suggests that although ideas and extensions possess the properties of parallel partially ordered structures, ideas are not dual to extensions and it is anachronistic to read into the Logic an early form of Boolean algebra. It shows that the Logic’s account of analysis and synthesis draws from a long tradition of syllogistic paradigms, and that although the formal logic it assumes is limited to the syllogistic, its analysis of the concept of “logical inference” is rule-governed and formal, similar to that of modern logic.