Necessity has been called the mother of invention. In philosophy, however, the notion of necessity is viewed in a different and somewhat more controversial light. In certain philosophical circles necessity is viewed as the root of much, if not all, philosophical error. In the latter half of the twentieth century, W. V. Quine, one of America’s most influential philosophers, claimed that the logic of necessity, now referred to as modal logic, was conceived in sin: the (logical) sin of confusing use with mention. In this philosophical environment, Saul Kripke published his earliest work on modal logic. Kripke’s work in modal logic was to have a major influence on the development of modal logic and philosophy in the future. It also was the foundation of many of Kripke’s later philosophical contributions. To understand Kripke’s early work, it will be helpful to begin by briefly reviewing developments in logic through the twentieth century.